This is assuan.info, produced by makeinfo version 6.3 from assuan.texi. INFO-DIR-SECTION GNU Libraries START-INFO-DIR-ENTRY * Assuan: (assuan). An IPC library for non-persistent servers. END-INFO-DIR-ENTRY This file documents the use and the internals of Assuan. This is Edition 2.5.3, last updated 7 December 2017, of 'The 'Developing with Assuan' Manual', for Version 2.5.3. Published by the Free Software Foundation 51 Franklin Street, Fifth Floor Boston, MA 02110-1301 USA Copyright (C) 2001-2013 Free Software Foundation, Inc. Copyright (C) 2001-2015 g10 Code GmbH Permission is granted to copy, distribute and/or modify this document under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3 of the License, or (at your option) any later version. The text of the license can be found in the section entitled "Copying".  File: assuan.info, Node: Top, Next: Introduction, Up: (dir) Introduction ************ This manual documents how to exploit the Assuan library, a simple interprocess communcation library. * Menu: * Introduction:: An introduction to and the motivation behind Assuan. * Assuan:: Description of the Assuan protocol. * Implementation:: Overview of the implementation. * Preparation:: What you should do before using the library. * Generalities:: Initialization code and data types used. * Client code:: How to develop an Assuan client. * Server code:: How to develop an Assuan server. * External I/O Loop:: How to use external I/O event loops. * Utilities:: Utility functions. * Socket wrappers:: Socket wrapper functions. Miscellaneous * Library Copying:: GNU Lesser General Public License says how you can copy and share Assuan. * Copying:: How you can copy and share this manual. Indices * Index:: Index of concepts and symbol names.  File: assuan.info, Node: Introduction, Next: Assuan, Prev: Top, Up: Top 1 Introduction to Assuan ************************ Assuan is an extensible inter-process communication (IPC) protocol and library. It is designed for point-to-point communication and it doesn't provide a naming system. To contact a server, either the client must know how to locate the server, e.g., via a well-known Unix domain socket, or, if the server is transient, how to start it. In the latter case, Assuan provides functionality to start the server process. In Assuan, communication is typically either via a pipe or a Unix domain socket. This method is neither elegant nor efficient, especially when there is a lot of data spread across several transactions. Not only is there a penalty for an increased number of context switches, but a significant amount of data is MEMCPYed from the client to a file descriptor and from the file descriptor to the server. Despite these and other disadvantages, this type of client/server communication is useful: the client is separated from the server: they run in different address spaces. This is especially important in situations where the server must have a known degree of reliability and data must be protected: as the Assuan protocol is well defined and clients cannot corrupt the servers' address space, auditing becomes much easier. Assuan was developed for use by the GNU Privacy Guard (GnuPG) to prevent potentially buggy clients from unwittingly corrupting sensitive transactions or compromising data such as a secret key. Assuan permits the servers, which do the actual work, e.g., encryption and decryption of data using a secret key, to be developed independently of the user interfaces, e.g., mail clients and other encryption front ends. Like a shared library, the interface is well defined and any number of front ends can use it; however, unlike a shared library, the client cannot see or touch the server's data. As with any modular system, Assuan helps keep the components small, understandable and less error prone. Assuan is not, however, limited to use with GnuPG servers and clients: it was designed to be flexible enough to meet the demands of many transaction-based environments.  File: assuan.info, Node: Assuan, Next: Implementation, Prev: Introduction, Up: Top 2 Description of the Assuan protocol. ************************************* The architecture of the modular GnuPG system is based on several highly specialized modules which form a network of clients and servers. A common framework for intermodule communication is therefore needed and implemented as a library. Goals: * Common framework for module communication * Easy debugging * Easy module testing * Extensible * Optional authentication and encryption facility * Usable to access external hardware Design criteria: * Client/Server with back channel * Use a mainly text based protocol * Escape certain control characters * Allow indefinite data length * Request confidentiality for parts of the communication * Dummy module to allow direct linking of client and server * Inline data or descriptor passing for bulk data * No protection against DoS needed * Subliminal channels are not an issue  File: assuan.info, Node: Implementation, Next: Preparation, Prev: Assuan, Up: Top 3 Implementation **************** The implementation is line based with a maximum line size of 1000 octets. The default IPC mechanism is Unix Domain Sockets. On connect, the server responds either with okay or an error status. To perform an authentication check, the server may send an Inquiry response prior to the first Okay. It may also issue Status messages. The server must check that the client is allowed to connect. This is done by requesting the credentials for the peer and comparing them with the server's credentials. This avoids attacks based on wrong socket permissions. The server may choose to delay the first response in case of an error. The server, however, never closes the connection, however, the lower protocol may do so after some time of inactivity or when the connection enters an error state. All textual messages are assumed to be in UTF-8 unless otherwise noted. * Menu: * Server responses:: Description of server responses. * Client requests:: Description of client requests. * Error codes:: List of error and status codes.  File: assuan.info, Node: Server responses, Next: Client requests, Up: Implementation 3.1 Server responses ==================== 'OK []' Request was successful. 'ERR ERRORCODE []' Request could not be fulfilled. The possible error codes are defined by 'libgpg-error'. 'S KEYWORD ' Informational output by the server, which is still processing the request. A client may not send such lines to the server while processing an Inquiry command. KEYWORD shall start with a letter or an underscore. '# ' Comment line issued only for debugging purposes. Totally ignored. 'D ' Raw data returned to client. There must be exactly one space after the 'D'. The values for '%', CR and LF must be percent escaped; these are encoded as %25, %0D and %0A, respectively. Only uppercase letters should be used in the hexadecimal representation. Other characters may be percent escaped for easier debugging. All Data lines are considered one data stream up to the OK or ERR response. Status and Inquiry Responses may be mixed with the Data lines. 'INQUIRE KEYWORD ' The server needs further information from the client. The client should respond with data (using the "D" command and terminated by "END"). Alternatively, the client may cancel the current operation by responding with "CAN". Consider the following examples (lines prefixed with S indicate text that the server sends; lines prefixed with C indicate text that the client sends): S: INQUIRE foo C: D foo bar C: D bar baz C: END [Server continues normal work] This implements a callback to the client: S: INQUIRE foo C: END [Server continues] and: S: INQUIRE foo C: CAN [Server terminates the operaion and in most cases returns an ERR to the client.] But, CAN may also mean "I have no data for you, try to get it from elsewhere." Note: lines longer than 1000 bytes should be treated as a communication error. (The rationale for having a line length limit is to allow for easier multiplexing of several channels.)  File: assuan.info, Node: Client requests, Next: Error codes, Prev: Server responses, Up: Implementation 3.2 Client requests =================== The server waits for client requests after sending an Okay or Error. The client should not issue a request in other cases. COMMAND COMMAND is a one word string without preceding white space. Parameters are command specific, CR, LF and the percent signs should be percent escaped as described above. To send a backslash as the last character it should also be percent escaped. Percent escaping is allowed anywhere in the parameters but not in the command. The line ends with a CR, LF pair or just a LF. Not yet implemented feature: If there is a need for a parameter list longer than the line length limit (1000 characters including command and CR, LF), the last character of the line (right before the CR/LF or LF) must be a unescaped (i.e., literal) backslash. The following line is then expected to be a continuation of the line with the backslash replaced by a blank and the line ending removed. D Sends raw data to the server. There must be exactly one space after the 'D'. The values for '%', CR and LF must be percent escaped. These are encoded as %25, %0D and %0A, respectively. Only uppercase letters should be used in the hexadecimal representation. Other characters may be percent escaped for easier debugging. All Data lines are considered one data stream up to the 'OK' or 'ERR' response. Status and Inquiry Responses may be mixed with the Data lines. END Lines beginning with a '#' or empty lines are ignored. This is useful to comment test scripts. Although the commands are application specific, some of them are used by all protocols and partly supported by the Assuan library: 'BYE' Close the connection. The server will respond with 'OK'. 'RESET' Reset the connection but not any existing authentication. The server should release all resources associated with the connection. 'END' Used by a client to mark the end of raw data. The server may send 'END' to indicate a partial end of data. 'HELP' Lists all commands that the server understands as comment lines on the status channel. 'QUIT' Reserved for future extensions. 'OPTION' Set options for the connection. The syntax of such a line is OPTION NAME [ [=] VALUE ] Leading and trailing spaces around NAME and VALUE are allowed but should be ignored. For compatibility reasons, NAME may be prefixed with two dashes. The use of the equal sign is optional but suggested if VALUE is given. 'CANCEL' This command is reserved for future extensions. 'AUTH' This command is reserved for future extensions. Not yet specified as we don't implement it in the first phase. See Werner's mail to gpa-dev on 2001-10-25 about the rationale for measurements against local attacks. 'NOP' No operation. Returns OK without any action.  File: assuan.info, Node: Error codes, Prev: Client requests, Up: Implementation 3.3 Error codes =============== Libassuan is used with gpg-error style error codes. It is recommended to set the error source to a different value from the default 'GPG_ERR_SOURCE_UNKNOWN' by calling *note function assuan_set_gpg_err_source:: early.  File: assuan.info, Node: Preparation, Next: Generalities, Prev: Implementation, Up: Top 4 Preparation ************* To use ASSUAN, you have to make some changes to your sources and the build system. The necessary changes are small and explained in the following sections. * Menu: * Header:: What header file you need to include. * Building sources:: How to build sources using the library. * Automake:: How to build sources with the help of Automake. * Multi Threading:: How 'libassuan' can be used in a MT environment.  File: assuan.info, Node: Header, Next: Building sources, Up: Preparation 4.1 Header ========== All interfaces (data types and functions) of 'libassuan' are defined in the header file 'assuan.h'. You must include this in all source files using the library, either directly or through some other header file, like this: #include The namespace of 'libassuan' is 'assuan_*' for function and type names and 'ASSUAN*' for other symbols. In addition the same name prefixes with one prepended underscore are reserved for internal use and should never be used by an application. Because 'libassuan' makes use of the GPG Error library, using 'libassuan' will also use the 'GPG_ERR_*' namespace directly, and the 'gpg_err*' and 'gpg_str*' namespaces indirectly.  File: assuan.info, Node: Building sources, Next: Automake, Prev: Header, Up: Preparation 4.2 Building sources ==================== If you want to compile a source file including the 'assuan.h' header file, you must make sure that the compiler can find it in the directory hierarchy. This is accomplished by adding the path to the directory in which the header file is located to the compilers include file search path (via the '-I' option). However, the path to the include file is determined at the time the source is configured. To solve this problem, 'libassuan' ships with a small helper program 'libassuan-config' that knows the path to the include file and other configuration options. The options that need to be added to the compiler invocation at compile time are output by the '--cflags' option to 'libassuan-config'. The following example shows how it can be used at the command line: gcc -c foo.c $(libassuan-config --cflags) Adding the output of 'libassuan-config --cflags' to the compiler's command line will ensure that the compiler can find the 'assuan.h' header file. A similar problem occurs when linking the program with the library. Again, the compiler/linker has to find the library files. For this to work, the path to the library files has to be added to the library search path (via the '-L' option). For this, the option '--libs' to 'libassuan-config' can be used. For convenience, this option also outputs all other options that are required to link the program with the 'libassuan' libraries (in particular, the '-lassuan' option). The example shows how to link 'foo.o' with the 'libassuan' library to a program 'foo'. gcc -o foo foo.o $(libassuan-config --libs) You can also combine both examples to a single command by specifying both options to 'libassuan-config': gcc -o foo foo.c $(libassuan-config --cflags --libs)  File: assuan.info, Node: Automake, Next: Multi Threading, Prev: Building sources, Up: Preparation 4.3 Building sources using Automake =================================== It is much easier if you use GNU Automake instead of writing your own Makefiles. If you do that you do not have to worry about finding and invoking the 'libassuan-config' script at all. 'libassuan' provides an Automake macro that does all the work for you. -- Macro: AM_PATH_LIBASSUAN ([MINIMUM-VERSION], [ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND]) Check whether 'libassuan' (at least version MINIMUM-VERSION, if given) exists on the host system. If it is found, execute ACTION-IF-FOUND, otherwise do ACTION-IF-NOT-FOUND, if given. Additionally, the function defines 'LIBASSUAN_CFLAGS' to the flags needed for compilation of the program to find the 'assuan.h' header file, and 'LIBASSUAN_LIBS' to the linker flags needed to link the program to the 'libassuan' library. You can use the defined Autoconf variables like this in your 'Makefile.am': AM_CPPFLAGS = $(LIBASSUAN_CFLAGS) LDADD = $(LIBASSUAN_LIBS)  File: assuan.info, Node: Multi Threading, Prev: Automake, Up: Preparation 4.4 Multi Threading =================== The 'libassuan' library is designed so that it can be used in a threaded application, if some rules are followed. * Run the initialization functions before you actually start to use threads. Specifically, the functions 'assuan_set_gpg_err_source', 'assuan_set_malloc_hooks' and 'assuan_set_log_cb' should not be called concurrently with 'assuan_new'. Use 'assuan_new_ext' instead or ensure proper serialization. * Only one thread at a time may access an 'libassuan' context. * If you use the default log handler, use 'assuan_set_assuan_log_stream' to setup a default log stream. * If you have callback functions shared by multiple functions, the callback function must be reentrant for that purpose. 'libassuan' does not serialize invocation of callback functions across contexts.  File: assuan.info, Node: Generalities, Next: Client code, Prev: Preparation, Up: Top 5 Generalities ************** * Menu: * Data Types:: Data types used by 'libassuan'. * Initializing the library:: How to initialize the library. * Default Log Handler:: How to configure the default log handler. * Contexts:: How to work with contexts. * Reading and Writing:: How to communicate with the peer.  File: assuan.info, Node: Data Types, Next: Initializing the library, Up: Generalities 5.1 Data Types used by the library ================================== ASSUAN uses a so-called context to store a connection's state. The following data type is used for that: -- Data type: assuan_context_t The 'assuan_context_t' type is a pointer to an object maintained internally by the library. Contexts are allocated with 'assuan_new' or 'assuan_new_ext' and released with 'assuan_release'. Other functions take this data type to access the state created by these functions. -- Data type: assuan_fd_t The 'assuan_fd_t' is a file descriptor (in Unix) or a system handle (in Windows). The special value 'ASSUAN_INVALID_FD' is used to specify invalid Assuan file descriptors. -- Function: assuan_fd_t assuan_fdopen (int FD) Create an assuan file descriptor from a POSIX (libc) file descriptor FD. On Unix, this is equivalent to 'dup', while on Windows this will retrieve the underlying system handle with '_get_osfhandle' and duplicate that.  File: assuan.info, Node: Initializing the library, Next: Default Log Handler, Prev: Data Types, Up: Generalities 5.2 Initializing the library ============================ Libassuan makes use of Libgpg-error and assumes that Libgpg-error has been initialized. In general 'gpgrt_check_version' should be called to guarantee this; the Libgpg-error manual for details. Libassuan itself requires no initialization. There are however some initialization hooks provided which are often useful. These should be called as early as possible and in a multi-threaded application before a second thread is created. These functions initialize default values that are used at context creation with 'assuan_new'. As there can only be one default, all values can also be set directly with 'assuan_new_ext' or with context-specific functions after context creation. If your application uses its own memory allocation functions or wrappers it is good idea to tell 'libassuan' about it so it can make use of the same functions or wrappers: -- Data type: struct assuan_malloc_hooks This structure is used to store the memory allocation callback interface functions. It has the following members, whose semantics are identical to the corresponding system functions: 'void *(*malloc) (size_t cnt)' This is the function called by ASSUAN to allocate memory for a context. 'void *(*realloc) (void *ptr, size_t cnt)' This is the function called by ASSUAN to reallocate memory for a context. 'void (*free) (void *ptr)' This is the function called by ASSUAN to release memory for a context. -- Data type: assuan_malloc_hooks_t This is a pointer to a 'struct assuan_malloc_hooks'. -- Function: void assuan_set_malloc_hooks (assuan_malloc_hooks_t MALLOC_HOOKS) This function sets the default allocation hooks for new contexts allocated with 'assuan_new'. You need to provide all three functions. Those functions need to behave exactly as their standard counterparts 'malloc', 'realloc' and 'free'. If you write your own functions, please take care to set 'errno' whenever an error has occurred. -- Function: assuan_malloc_hooks_t assuan_get_malloc_hooks () This function gets the default allocation hooks for new contexts allocated with 'assuan_new'. The result structure is statically allocated and should not be modified. The ASSUAN library uses 'libgpg-error' error values, which consist and error code and an error source. The default source used by contexts allocated with 'assuan_new' can be set with the following function. -- Function: void assuan_set_gpg_err_source (gpg_err_source_t ERR_SOURCE) This function sets the default error source for errors generated by contexts allocated with 'assuan_new'. One way to call this function is assuan_set_gpg_err_source (GPG_ERR_SOURCE_DEFAULT); -- Function: gpg_err_source_t assuan_get_gpg_err_source (void) This function gets the default error source for errors generated by contexts allocated with 'assuan_new'. To integrate assuan logging and diagnostics into your own logging system, you may use the following two functions: -- Data type: int (*assuan_log_cb_t) (assuan_context_t CTX, void *HOOK_VALUE, unsigned int CAT, const char *MSG) The user-provided callback function takes a context CTX, for which the message MSG was generated, and a hook value HOOK_VALUE that was supplied when the log handler was registered for the context with 'assuan_set_log_cb', and a category CAT. The category is one of: 'ASSUAN_LOG_INIT' 'ASSUAN_LOG_CTX' 'ASSUAN_LOG_ENGINE' 'ASSUAN_LOG_DATA' RFU 'ASSUAN_LOG_SYSIO' Log lowlevel I/O data. 'ASSUAN_LOG_CONTROL' Log the control channel. The user may then, depending on the category, write the message to a log file or treat it in some other way. If MSG is a null pointer, then no message should be logged, but the function should return 1 if it is interested in log messages with the category CAT. If it is not interested, 0 should be returned. This allows 'libassuan' to suppress the generation of expensive debug output. -- Function: void assuan_set_log_cb (assuan_log_cb_t LOG_CB, void *LOG_CB_DATA) This function sets the default logging handler for log messages generated by contexts allocated with 'assuan_new'. -- Function: void assuan_get_log_cb (assuan_log_cb_t *LOG_CB, void **LOG_CB_DATA) This function gets the default logging handler for log messages generated by contexts allocated with 'assuan_new'. You do not need to set a log handler, as ASSUAN provides a configurable default log handler that should be suitable for most purposes. Logging can be disabled completely by setting the log handler to a null pointer.  File: assuan.info, Node: Default Log Handler, Next: Contexts, Prev: Initializing the library, Up: Generalities 5.3 Default Log Handler ======================= The default log handler can be configured by the following functions: -- Function: void assuan_set_assuan_log_prefix (const char *TEXT) Set the prefix to be used at the start of a line emitted by assuan on the log stream to TEXT. The default is the empty string. -- Function: const char * assuan_get_assuan_log_prefix (void) Return the prefix to be used at the start of a line emitted by assuan on the log stream. The default implementation returns the empty string. -- Function: void assuan_set_assuan_log_stream (FILE *FP) This sets the default log stream to which 'libassuan' should log messages not associated with a specific context to FP. The default is to log to 'stderr'. This default value is also changed by using 'assuan_set_log_stream' (to set a logging stream for a specific context) unless this function has been used. Obviously this is not thread-safe and thus it is highly recommended to use this function to setup a proper default. -- Function: FILE * assuan_get_assuan_log_stream (void) Return the stream which is currently being using for global logging. The log stream used by the default log handler can also be set on a per context basis. -- Function: void assuan_set_log_stream (assuan_context_t CTX, FILE *FP) Enable debugging for the context CTX and write all debugging output to the stdio stream FP. If the default log stream (used for non-context specific events) has not yet been set, a call to this functions implicitly sets this stream also to FP.  File: assuan.info, Node: Contexts, Next: Reading and Writing, Prev: Default Log Handler, Up: Generalities 5.4 How to work with contexts ============================= Some operations work globally on the library, but most operate in a context, which saves state across operations. To allow the use of 'libassuan' in mixed environments, such as in a library using GPGME and an application using GPGME, the context is very extensive and covers utilitary information like memory allocation callbacks as well as specific information associated with client/server operations. -- Function: gpg_error_t assuan_new (assuan_context_t *CTX_P) The function 'assuan_new' creates a new context, using the global default memory allocation, log handler and 'libgpg-error' source. It is equivalent to gpg_error_t err; assuan_log_cb_t log_cb; void *log_cb_data; assuan_get_log_cb (&log_cb, &log_cb_data); err = assuan_new_ext (ctx_p, assuan_get_gpg_err_source (), assuan_get_malloc_hooks (), log_cb, log_cb_data); As you can see, this is not thread-safe. Take care not to modify the memory allocation hooks or log callback handler concurrently with 'assuan_new'. The function returns an error if a memory allocation error occurs, and 0 with the new context in CTX_P otherwise. -- Function: gpg_error_t assuan_new_ext (assuan_context_t *CTX_P, gpg_err_source_t ERR_SOURCE, assuan_malloc_hooks_t MALLOC_HOOKS, assuan_log_cb_t LOG_CB, void *LOG_CB_DATA) The function 'assuan_new_ext' creates a new context using the supplied 'libgpg-error' error source ERR_SOURCE, the memory allocation hooks MALLOC_HOOKS and the log handler LOG_CB with the user data LOG_CB_DATA. After the context has been used, it can be destroyed again. -- Function: void assuan_release (assuan_context_t ctx) The function 'assuan_release' destroys the context CTX and releases all associated resources. Other properties of the context beside the memory allocation handler, the log handler, and the 'libgpg-error' source can be set after context creation. Here are some of them: -- Function: void assuan_set_pointer (assuan_context_t CTX, void *POINTER) Store the arbitrary pointer value POINTER into the context CTX. This is useful to provide command handlers with additional application context. -- Function: void* assuan_get_pointer (assuan_context_t CTX) This returns the pointer for context CTX which has been set using the above function. A common way to use it is by setting the pointer before starting the processing loop and to retrieve it right at the start of a command handler: static int cmd_foo (assuan_context_t ctx, char *line) { ctrl_t ctrl = assuan_get_pointer (ctx); ... } -- Function: void assuan_set_flag (assuan_context_t CTX, assuan_flag_t FLAG, int VALUE) Set the the FLAG for context CTX to VALUE. Values for flags are usually 1 or 0 but certain flags might need other values. -- Data type: assuan_flag_t The flags are all named and collected in an 'enum' for better readability. Available flags are: 'ASSUAN_NO_WAITPID' When using a pipe server, by default Libassuan will wait for the forked process to die in 'assuan_release'. In certain cases this is not desirable. By setting this flag, a call to 'waitpid' will be suppressed and the caller is responsible to cleanup the child process. 'ASSUAN_CONFIDENTIAL' Use to return the state of the confidential logging mode. 'ASSUAN_NO_FIXSIGNALS' Do not modify signal handler for 'SIGPIPE'. 'ASSUAN_CONVEY_COMMENTS' If enabled comment lines are passed to the status callback of the 'assuan_transact'. 'ASSUAN_FORCE_CLOSE' Setting this flag forces the next command to assume that the connection has been closed. This breaks the command processing loop and may be used as an implicit BYE command. VALUE is ignored and thus it is not possible to clear this flag. -- Function: int assuan_get_flag (assuan_context_t CTX, assuan_flag_t FLAG) Return the value of FLAG in context CTX. -- Function: void assuan_begin_confidential (assuan_context_t CTX) Put the logging feature into confidential mode. This is to avoid logging of sensitive data. This is identical to: assuan_set_flag (ctx, ASSUAN_CONFIDENTIAL, 1); -- Function: void assuan_end_confidential (assuan_context_t CTX) Get the logging feature out of confidential mode. All data will be logged again (if logging is enabled). This is identical to: assuan_set_flag (ctx, ASSUAN_CONFIDENTIAL, 0); -- Data type: struct assuan_system_hooks This structure is used to store the system callback interface functions. It has the following members, whose semantics are similar to the corresponding system functions, but not exactly equivalent. 'int version' The user should set this to 'ASSUAN_SYSTEM_HOOKS_VERSION'. This indicates to the library which members of this structure are present in case of future extensions. The user should initialize the whole structure with zero bytes. 'void (*usleep) (assuan_context_t ctx, unsigned int usec)' This is the function called by ASSUAN to sleep for 'USEC' microseconds. 'int (*pipe) (assuan_context_t ctx, assuan_fd_t fd[2], int inherit_idx)' This is the function called by ASSUAN to create a pipe. The returned file descriptor 'fd[inherit_idx]' must be inheritable by the child process (under Windows, this requires some extra work). 'int (*close) (assuan_context_t ctx, assuan_fd_t fd)' This is the function called by ASSUAN to close a file descriptor created through the system functions. 'ssize_t (*read) (assuan_context_t ctx, assuan_fd_t fd, void *buffer, size_t size)' This is the function called by ASSUAN to read data from a file descriptor. It is functionally equivalent to the system 'read' function. 'ssize_t (*write) (assuan_context_t ctx, assuan_fd_t fd, const void *buffer, size_t size)' This is the function called by ASSUAN to write data to a file descriptor. It is functionally equivalent to the system 'write' function. 'int (*recvmsg) (assuan_context_t ctx, assuan_fd_t fd, assuan_msghdr_t msg, int flags)' This is the function called by ASSUAN to receive a message from a file descriptor. It is functionally equivalent to the system 'recvmsg' function. 'int (*sendmsg) (assuan_context_t ctx, assuan_fd_t fd, const assuan_msghdr_t msg, int flags);' This is the function called by ASSUAN to send a message to a file descriptor. It is functionally equivalent to the system 'sendmsg' function. 'int (*spawn) (assuan_context_t ctx, pid_t *r_pid, const char *name, const char **argv, assuan_fd_t fd_in, assuan_fd_t fd_out, assuan_fd_t *fd_child_list, void (*atfork) (void *opaque, int reserved), void *atforkvalue, unsigned int flags)' This is the function called by ASSUAN to spawn a child process. The 'stdin' and 'stdout' file descriptors are provided in 'fd_in' and 'fd_out' respectively, but can be set to 'ASSUAN_INVALID_FD', in which case they are set to '/dev/null'. On systems which use 'fork' and 'exec', the 'atfork' function should be called with 'atforkvalue' and '0' for flags in the child process right after 'fork' returns. 'fd_child_list' is a 'ASSUAN_INVALID_FD' terminated array (or 'NULL') and specifies file descriptors to be inherited by the child process. A special situation occurs if 'name' is a null pointer, in which case the process should just fork but not call 'exec'. In this case, '*argv' should be set to '"client"' in the parent process and '"server"' in the child process. Flags is the bit-wise OR of some (or none) of the following flags: 'ASSUAN_SPAWN_DETACHED' If set and there is a need to start the server it will be started as a background process. This flag is useful under W32 systems, so that no new console is created and pops up a console window when starting the server. On W32CE systems this flag is ignored. 'pid_t (*waitpid) (assuan_context_t ctx, pid_t pid, int action, int *status, int options)' This is the function called by ASSUAN to wait for the spawned child process PID to exit, or, if ACTION is 1, to just release all resources associated with PID (required on Windows platforms). If ACTION is 0, this is equivalent to 'waitpid'. 'int (*socketpair) (assuan_context_t ctx, int namespace, int style, int protocol, assuan_fd_t filedes[2])' This is the function called by ASSUAN to create a socketpair. It is equivalent to 'socketpair'. -- Function: void assuan_set_system_hooks (assuan_system_hooks_t SYSTEM_HOOKS) Set the default system hooks to use. There is currently no way to reset to the default system hooks. -- Function: void assuan_sock_set_system_hooks (assuan_system_hooks_t SYSTEM_HOOKS) The socket subsystem uses an internal context which uses the default system hooks. This function allows to change these system hooks. The function is not thread-safe and only useful if a certain order of assuan and assuan socket initializations are required. -- Function: void assuan_ctx_set_system_hooks (assuan_context_t CTX, assuan_system_hooks_t SYSTEM_HOOKS) Set the system hooks for context CTX. There is currently no way to reset to the default system hooks, create a new context for that. The following system hook collections are defined by the library for your convenience: 'ASSUAN_SYSTEM_NPTH' System hooks suitable for use with the nPth library. 'ASSUAN_SYSTEM_NPTH_IMPL' The implementation of system hooks for use with the nPth library. This must be invoked once somewhere in the application, and defines the structure that is referenced by 'ASSUAN_SYSTEM_NPTH'. 'ASSUAN_SYSTEM_PTH' System hooks suitable for use with the GNU Pth library. 'ASSUAN_SYSTEM_PTH_IMPL' The implementation of system hooks for use with the GNU Pth library. This must be invoked once somewhere in the application, and defines the structure that is referenced by 'ASSUAN_SYSTEM_PTH'.  File: assuan.info, Node: Reading and Writing, Prev: Contexts, Up: Generalities 5.5 How to communicate with the peer ==================================== What would be an IPC library without the ability to read and write data? Not very useful. Libassuan has high level functions to take care of of the more boring stuff, but eventually data needs to be written and read. The basic read and write functions are: -- Function: gpg_error_t assuan_read_line (assuan_context_t CTX, char **LINE, size_t *LINELEN) Read the next line written by the peer to the control channel and store a pointer to the buffer holding that line at the address LINE. The valid length of the lines is stored at the address of LINELEN. This buffer is valid until the next read operation on the same context CTX. You may modify the context of this buffer. The buffer is invalid (i.e. must not be used) if an error is returned. This function returns '0' on success or an error value. -- Function: gpg_error_t assuan_write_line (assuan_context_t CTX, const char *LINE) Write the string LINE to the other end on the control channel. This string needs to be a proper formatted Assuan protocol line and should not include a linefeed. Sending linefeed or 'Nul' characters is not possible and not allowed by the assuan protocol. This function shall not be used for sending data ('D') lines. This function returns '0' on success or an error value. To actually send bulk data lines a specialized function is available: -- Function: gpg_error_t assuan_send_data (assuan_context_t CTX, const void *BUFFER, size_t LENGTH) This function is used by a server or a client to send LENGTH bytes of bulk data in BUFFER to the other end on the control channel. The data will be escaped as required by the Assuan protocol and may get buffered until a line is full. To flush any pending data, BUFFER may be passed as 'NULL' and LENGTH be '0'. When used by a client, this flush operation does also send the 'END' command to terminate the response on an 'INQUIRE' request. Note that the function 'assuan_transact' takes care of sending this 'END' itself. This function returns '0' on success or an error value. The input and output of data can be controlled at a higher level using an I/O monitor. -- Data type: unsigned int (*assuan_io_monitor_t) (assuan_context_t CTX, void *HOOK_VALUE, int INOUT, const char *LINE, size_t LINELEN) The monitor function is called right after a line has been received, if INOUT is 'ASSUAN_IO_FROM_PEER', or just before it is send, if INOUT is 'ASSUAN_IO_TO_PEER'. The HOOK_VALUE is provided by the user when registering the I/O monitor function with a context using 'assuan_set_io_monitor'. The callback function should return the bitwise OR of some (or none) of the following flags: 'ASSUAN_IO_MONITOR_NOLOG' Active logging of this line is suppressed. This can reduce debug output in the case of a frequent message. 'ASSUAN_IO_MONITOR_IGNORE' The whole output line is discarded. -- Function: void assuan_set_io_monitor (assuan_context_t CTX, assuan_io_monitor_t IO_MONITOR, void *HOOK_DATA) This function registers an I/O monitor IO_MONITOR for the context CTX with the hook value HOOK_DATA.  File: assuan.info, Node: Client code, Next: Server code, Prev: Generalities, Up: Top 6 How to develop an Assuan client ********************************* Depending on the type of the server you want to connect you need to use different functions. If the peer is not a simple pipe server but one using full-duplex sockets, the full-fledged variant of the above function should be used: -- Function: gpg_error_t assuan_pipe_connect (assuan_context_t CTX,const char *NAME, const char *ARGV[], assuan_fd_t *FD_CHILD_LIST, void (*ATFORK) (void *, int), void *ATFORKVALUE, unsigned int FLAGS) A call to this functions forks the current process and executes the program NAME, passing the arguments given in the NULL-terminated list ARGV. A list of file descriptors not to be closed may be given using the 'ASSUAN_INVALID_FD' terminated array FD_CHILD_LIST. If NAME is a null pointer, only a fork but no exec is done. Thus the child continues to run. However all file descriptors are closed and some special environment variables are set. To let the caller detect whether the child or the parent continues, the parent returns with '"client"' returned in ARGV and the child returns with '"server"' in ARGV. This feature is only available on POSIX platforms. If ATFORK is not NULL, this function is called in the child right after the fork and the value ATFORKVALUE is passed as the first argument. That function should only act if the second argument it received is '0'. Such a fork callback is useful to release additional resources not to be used by the child. FLAGS is a bit vector and controls how the function acts: 'ASSUAN_PIPE_CONNECT_FDPASSING' If cleared a simple pipe based server is expected. If set a server based on full-duplex pipes is expected. Such pipes are usually created using the 'socketpair' function. It also enables features only available with such servers. 'ASSUAN_PIPE_CONNECT_DETACHED' If set and there is a need to start the server it will be started as a background process. This flag is useful under W32 systems, so that no new console is created and pops up a console window when starting the server. On W32CE systems this flag is ignored. If you are using a long running server listening either on a TCP or a Unix domain socket, the following function is used to connect to the server: -- Function: gpg_error_t assuan_socket_connect (assuan_context_t CTX, const char *NAME, pid_t SERVER_PID, unsigned int FLAGS) Make a connection to the Unix domain socket NAME using the already-initialized Assuan context at CTX. SERVER_PID is currently not used but may become handy in the future; if you don't know the server's process ID (PID), pass 'ASSUAN_INVALID_PID'. With FLAGS set to 'ASSUAN_SOCKET_CONNECT_FDPASSING', 'sendmsg' and 'recvmesg' are used for input and output and thereby enable the use of descriptor passing. Connecting to a TCP server is not yet implemented. Standard URL schemes are reserved for NAME specifying a TCP server. Now that we have a connection to the server, all work may be conveniently done using a couple of callbacks and the transact function: -- Function: gpg_error_t assuan_transact (assuan_context_t CTX, const char *COMMAND, gpg_error_t (*DATA_CB)(void *, const void *, size_t), void *DATA_CB_ARG, gpg_error_t (*INQUIRE_CB)(void*, const char *), void *INQUIRE_CB_ARG, gpg_error_t (*STATUS_CB)(void*, const char *), void *STATUS_CB_ARG) Here CTX is the Assuan context opened by one of the connect calls. COMMAND is the actual Assuan command string. It shall not end with a line feed and its length is limited to 'ASSUAN_LINELENGTH' (~1000 bytes) DATA_CB is called by Libassuan for data lines; DATA_CB_ARG is passed to it along with the data and the length. [FIXME: needs more documentation]. INQUIRE_CB is called by Libassuan when the server requests additional information from the client while processing the command. This callback shall check the provided inquiry name and send the data as requested back using the 'assuan_send_data'. The server passed INQUIRY_CB_ARG along with the inquiry name to the callback. STATUS_CB is called by Libassuan for each status line it receives from the server. STATUS_CB_ARG is passed along with the status line to the callback. The function returns '0' success or an error value. The error value may be the one one returned by the server in error lines or one generated by the callback functions. Libassuan supports descriptor passing on some platforms. The next two functions are used with this feature: -- Function: gpg_error_t assuan_sendfd (assuan_context_t CTX, assuan_fd_t FD) Send the descriptor FD to the peer using the context CTX. The descriptor must be sent before the command is issued that makes use of the descriptor. Note that calling this function with a CTX of 'NULL' and FD of 'ASSUAN_INVALID_FD' can be used as a runtime test to check whether descriptor passing is available on the platform: '0' is returned if descriptor passing is available, otherwise an error with the error code 'GPG_ERR_NOT_IMPLEMENTED' is returned. -- Function: gpg_error_t assuan_receivefd (assuan_context_t CTX, assuan_fd_t *FD) Receive a descriptor pending for the context CTX from the peer. The descriptor must be pending before this function is called. To accomplish this, the peer needs to use 'assuan_sendfd' before the trigger is sent (e.g. using 'assuan_write_line ("INPUT FD")'.  File: assuan.info, Node: Server code, Next: External I/O Loop, Prev: Client code, Up: Top 7 How to develop an Assuan server ********************************* Implementing a server for Assuan is a bit more complex than a client. However, it is a straightforward task we are going to explain using a commented example. The list of the implemented server commands is defined by a table like: static struct { const char *name; int (*handler) (assuan_context_t, char *line); } command_table[] = { { "FOO", cmd_foo }, { "BAR", cmd_bar }, { "INPUT", NULL }, { "OUTPUT", NULL }, { NULL }}; For convenience this table is usually put after the actual command handlers ('cmd_foo', 'cmd_bar') or even put inside 'command_handler' (see below). Note that the commands 'INPUT' and 'OUTPUT' do not require a handler because Libassuan provides a default handler for them. It is however possible to assign a custom handler. A prerequisite for this example code is that a client has already connected to the server. Often there are two modes combined in one program: A pipe-based server, where a client has forked the server process, or a Unix domain socket based server that is listening on the socket. void command_handler (int fd) { gpg_error_t rc; int i; assuan_context_t ctx; rc = assuan_new (&ctx); if (rc) { fprintf (stderr, "server context creation failed: %s\n", gpg_strerror(rc)); return; } if (fd == -1) { assuan_fd_t filedes[2]; filedes[0] = assuan_fd_from_posix_fd (0); filedes[1] = assuan_fd_from_posix_fd (1); rc = assuan_init_pipe_server (ctx, filedes); } else rc = assuan_init_socket_server (ctx, fd, ASSUAN_SOCKET_SERVER_ACCEPTED); if (rc) { fprintf (stderr, "server init failed: %s\n", gpg_strerror (rc)); return; } This is the first part of the command handler. We start off by allocating a new Assuan context with 'assuan_new'. *Note function assuan_new::. In case this is called as a pipe based server, FD will be based as FD and the code assumes that the server's 'stdin' and 'stdout' file handles are connected to a pipe. The initialization is thus done using the function: -- Function: gpg_error_t assuan_init_pipe_server (assuan_context_t CTX, assuan_fd_t FILEDES[2]) This function takes the two file descriptors from FILEDES and returns a new Assuan context at R_CTX. As usual, a return value of '0' indicates success and a failure is indicated by returning an error value. In case of error, 'NULL' will be stored at R_CTX. In case the server has been called using a bi-directional pipe (socketpair), FILEDES is ignored and the file descriptor is taken from the environment variable '_assuan_connection_fd'. You generally don't need to know this, because 'assuan_pipe_connect', which is called by the client to connect to such a server, automagically sets this variable. -- Function: gpg_error_t assuan_init_socket_server (assuan_context_t CTX, assuan_fd_t FD, unsigned int FLAGS) This function takes the file descriptor FD, which is expected to be associated with a socket, and an Assuan context CTX. The following bits are currently defined for FLAGS: 'ASSUAN_SOCKET_SERVER_FDPASSING' If set, 'sendmsg' and 'recvmesg' are used for input and output, which enables the use of descriptor passing. 'ASSUAN_SOCKET_SERVER_ACCEPTED' If set, FD refers to an already accepted socket. That is, Libassuan won't call ACCEPT for it. It is suggested to set this bit as it allows better control of the connection state. As usual, a return value of '0' indicates success and a failure is indicated by returning an error value. On the Windows platform the following function needs to be called after 'assuan_init_socket_server': -- Function: void assuan_set_sock_nonce ( assuan_context_t CTX, assuan_sock_nonce_t *NONCE) Save a copy of NONCE in context CTX. This should be used to register the server's nonce with a context established by 'assuan_init_socket_server'. It is technically only needed for Windows, but it does no harm to use it on other systems. After error checking, the implemented assuan commands are registered with the server. for (i = 0; command_table[i].name; i++) { rc = assuan_register_command (ctx, command_table[i].name, command_table[i].handler, NULL); if (rc) { fprintf (stderr, "register failed: %s\n", gpg_strerror (rc)); assuan_release (ctx); return; } } -- Data type: gpg_error_t (*assuan_handler_t) (assuan_context_t CTX, char *LINE) This is the function invoked by ASSUAN for various command related callback functions. Some of these callback functions have a different type, but most use 'assuan_handler_t'. -- Function: gpg_error_t assuan_register_command (assuan_context_t CTX, const char *CMD_STRING, assuan_handler_t HANDLER, const char *HELP_STRING) This registers the command named CMD_STRING with the Assuan context CTX. HANDLER is the function called by Libassuan if this command is received from the client. NULL may be used for HANDLER to use a default handler (this only works with a few pre-defined commands). Note that several default handlers have already been registered when the context has been created: 'NOP', 'CANCEL', 'OPTION', 'BYE', 'AUTH', 'RESET' and 'END'. It is possible, but not recommended, to override these commands. HELP_STRING is a help string that is used for automatic documentation. It should contain a usage line followed by an empty line and a complete description. -- Function: gpg_error_t assuan_register_post_cmd_notify (assuan_context_t CTX, void (*FNC)(assuan_context_t), gpg_error_t ERR) Register a function to be called right after a command has been processed. ERR is the result code from the last internal assuan operation and not the one returned by the handler. It may be used for command-related cleanup. -- Function: gpg_error_t assuan_register_bye_notify (assuan_context_t CTX, assuan_handler_t HANDLER) Register function FNC with context CTX to be called right before the standard handler for the 'BYE' command is being called. -- Function: gpg_error_t assuan_register_reset_notify (assuan_context_t CTX, assuan_handler_t HANDLER) Register function FNC with context CTX to be called right before the standard handler for the 'RESET' command is being called. -- Function: gpg_error_t assuan_register_cancel_notify (assuan_context_t CTX, assuan_handler_t HANDLER) Register function FNC with context CTX to be called right before the standard handler for the 'RESET' command is being called. -- Function: gpg_error_t assuan_register_option_handler (assuan_context_t CTX, gpg_error_t (*FNC)(assuan_context_t, const char*, const char*)) Register function FNC with context CTX for processing options. That function is being called with the context, the name and the value of the option. Leading and trailing spaces are removed from the name and the value. The optional leading two dashes of the name are removed as well. If no value has been given, an empty string is passed. The function needs to return '0' on success or an error code. -- Function: gpg_error_t assuan_register_input_notify (assuan_context_t CTX, assuan_handler_t HANDLER) Although the input function may be overridden with a custom handler, it is often more convenient to use the default handler and to know whether an 'INPUT' command has been seen and successfully parsed. The second argument passed to that function is the entire line. Because that line has already been parsed when the function gets called, a file descriptor set with the 'INPUT' command may already be used. That file descriptor is available by calling 'assuan_get_input_fd'. If the notification function returns an error, the input fd does not change. -- Function: gpg_error_t assuan_register_output_notify (assuan_context_t CTX, assuan_handler_t HANDLER) Although the output function may be overridden with a custom handler, it is often more convenient to use the default handler and to know whether an 'OUTPUT' command has been seen and successfully parsed. The second argument passed to that function is the entire line. Because that line has already been parsed when the function gets called, a file descriptor set with the 'OUTPUT' command may already be used. That file descriptor is available by calling 'assuan_get_output_fd'. If the notification function returns an error, the output fd does not change. -- Function: gpg_error_t assuan_set_hello_line (assuan_context_t CTX, const char *LINE) This is not actually a register function but may be called also after registering commands. It changes the "Hello" line, sent by the server to the client as a first response, from a default string to the string LINE. For logging purposes, it is often useful to use such a custom hello line which may tell version numbers and such. Linefeeds are allowed in this string, however, each line needs to be shorter than the Assuan line length limit. Now that everything has been setup, we can start to process our clients requests. for (;;) { rc = assuan_accept (ctx); if (rc == -1) break; else if (rc) { fprintf (stderr, "accept problem: %s\n", gpg_strerror (rc)); break; } rc = assuan_process (ctx); if (rc) { fprintf (stderr, "processing failed: %s\n", gpg_strerror (rc)); continue; } } assuan_release (ctx); } For future extensibility and to properly detect the end of the connection the core of the server should loop over the accept and process calls. -- Function: gpg_error_t assuan_accept (assuan_context_t CTX) A call to this function cancel any existing connection and waits for a connection from a client (that might be skipped, depending on the type of the server). The initial handshake is performed which may include an initial authentication or encryption negotiation. On success '0' is returned. An error value will be returned if the connection could for some reason not be established. An error code of 'GPG_ERR_EOF' indicates the end of the connection. -- Function: gpg_error_t assuan_process (assuan_context_t CTX) This function is used to handle the Assuan protocol after a connection has been established using 'assuan_accept'. It is the main protocol handler responsible for reading the client commands and calling the appropriate handlers. The function returns '0' on success or an error value if something went seriously wrong. Error values from the individual command handlers, i.e. operational error, are not seen here. That is all needed for the server code. You only need to come up with the code for the individual command handlers. Take care that the line passed to the command handlers is allocated statically within the context and calls to Assuan functions may modify that line. You are also allowed to modify that line which makes parsing much easier.  File: assuan.info, Node: External I/O Loop, Next: Utilities, Prev: Server code, Up: Top 8 How to use external I/O event loops ************************************* The above implementations of an Assuan client and server are synchronous, insofar as the main routines block until a request or client connection is completely processed. In some programs, for example GUI applications, this is undesirable. Instead, Assuan operations should be non-blocking, and the caller should be able to poll all involved file descriptors to determine when the next Assuan function can be invoked without blocking. To make this possible, client and server have to adhere to some rules: * Either partner should always write full lines. If partial lines are written, the remainder of the line should be sent without delay. * Either partner should eagerly receive status messages. While receiving and sending bulk data may be delayed, the status communication channel is different: Both partners may send status messages in blocking mode at any time the protocol allows them to send such status messages. To ensure that these send operations do not actually block the sender, the recipient must be ready to receive without undue delay. * If descriptor passing is used over a socket, the descriptor must be sent after the corresponding command without undue delay. Together, these restrictions allow to limit the need for asynchronous I/O operations to bulk data and the inbound status file descriptor. In addition to the above rules, client and server should adhere to the following implementation guidelines. * Menu: * External I/O Loop Client:: External I/O event loops in the client. * External I/O Loop Server:: External I/O event loops in the server.  File: assuan.info, Node: External I/O Loop Client, Next: External I/O Loop Server, Up: External I/O Loop 8.1 External I/O event loops in the client. =========================================== The reference implementation for using external I/O event loops in the client is the GPGME library, which exports its own external I/O event loop mechanism and utilizes the Assuan library transparently for the user. The following steps document how GPGME achieves this. 1. Before connecting, set up pipes for bulk data transfer (using the INPUT/OUTPUT commands, for example). These are passed to the server either by inheritance (using a pipe server) or by FD passing (using a socket server). 2. Then you need to connect to the server. GPGME uses a pipe server, so it just spawns a server process, which is a non-blocking operation. FIXME: Currently, using a client with external event loop over a socket connection is not supported. It is easy to support (we just need a variation of 'assuan_socket_connect' which takes an already connected socket FD and turns it into an Assuan context), so if you need this let us know. 3. After connecting, get the inbound status FD with 'assuan_get_active_fds' (the first one returned is the status FD). This FD can be duplicated if it is convenient (GPGME does this to be able to close this FD and associated callback handlers without disrupting Assuan's internals). 4. Then register the Assuan inbound status FD and all bulk data FDs with the I/O event mechanism. In general, this requires setting up callback handlers for these FDs and registering them with the main event loop. 5. When bulk data FDs become ready, you can simply perform the corresponding read or write operations. When the inbound status FD becomes ready, you can receive the next server line with assuan_read_line(). 6. You should close and unregister the bulk data FDs when you wrote all data (for outbound FDs) or receive an EOF (for inbound FDs). When you receive an ERR from the server, or an OK for the final operation, you can unregister the inbound status FD and call 'assuan_release'. 7. As noted above, all send operations on the outbound status FD are done immediate with blocking. In GPGME, this has never caused any problems. 8. The 'INQUIRE' function can be handled in two ways: If the requested data is immediately available, the client can just send the data blockingly. If the requested data needs to be fetched from a blocking source, a callback handler can be registered for the FD with the main event loop. GPGME does not support the 'INQUIRE' function, so we do not have any practical experience with this. Currently, the client can not cancel a pending operation gracefully. It can, however, disconnect from the server at any time. It is the responsibility of the server to periodically send status messages to the client to probe if the connection remains alive.  File: assuan.info, Node: External I/O Loop Server, Prev: External I/O Loop Client, Up: External I/O Loop 8.2 External I/O event loops in the server. =========================================== Currently, no Assuan server exists which uses external I/O event loops. However, the following guidelines should lead to a usable implementation: 1. For socket servers: You can not use 'assuan_accept', so you should just implement the bind/connect/listen/accept stage yourself. You can register the listen FD with your main event loop, accept the connection when it becomes ready, and finally call 'assuan_init_socket_server' with the final argument being 'ASSUAN_SOCKET_SERVER_ACCEPTED' to create an Assuan context for this connection. This way you can also handle multiple connections in parallel. The reference implementation for this approach is DirMngr. For pipe servers: 'assuan_init_pipe_server' creates an Assuan context valid for the pipe FDs. 2. Once you have a context for a single connection, you can get the inbound status FD with 'assuan_get_active_fds' (the first one returned is the status FD). This FD can be duplicated if it is convenient. Every time the inbound status FD is readable, you should invoke the function 'assuan_process_next' (see below) to process the next incoming message. 'assuan_process_next' processes as many status lines as can be received by a single 'read' operation. When it returns, the inbound status FD may still be readable, but Assuan does not check this. The function 'assuan_process_next' returns 0 if it can not make progress reliably, and it returns true in 'done' if the client closed the connection. See below for more information on this function. 3. The command will be dispatched by 'assuan_process_next' just as with 'assuan_process', however, you will want to implement the command handlers in such a way that they do not block. For example, the command handler may just register the bulk data FDs with the main event loop and return. When the command is finished, irregardless if this happens directly in the command handler or later, you must call 'assuan_process_done' with an appropriate error value (or 0 for success) to return an appropriate status line to the client. You can do this at the end of the command handler, for example by ending it with 'return assuan_process_done (error_code);'. Another possibility is to invoke 'assuan_process_done' from the place in the code which closes the last active bulk FD registered with the main event loop for this operation. It is not possible to use 'assuan_inquire' in a command handler, as this function blocks on receiving the inquired data from the client. Instead, the asynchronous version 'assuan_inquire_ext' needs to be used (see below), which invokes a callback when the client provided the inquired data. A typical usage would be for the command handler to register a continuation with 'assuan_inquire_ext' and return 0. Eventually, the continuation would be invoked by 'assuan_process_next' when the client data arrived. The continuation could complete the command and eventually call 'assuan_process_done'. Cancellation is supported by returning an appropriate error value to the client with 'assuan_process_done'. For long running operations, the server should send progress status messages to the client in regular intervals to notice when the client disconnects. -- Function: gpg_error_t assuan_process_next (assuan_context_t CTX, int *DONE) This is the same as 'assuan_process' but the caller has to provide the outer loop. He should loop as long as the return code is zero and DONE is false. -- Function: gpg_error_t assuan_process_done (assuan_context_t CTX, gpg_error_t RC) Finish a pending command and return the error code RC to the client. -- Function: gpg_error_t assuan_inquire_ext (assuan_context_t CTX, const char *KEYWORD, size_t MAXLEN, gpg_error_t (*CB) (void *cb_data, gpg_error_t rc, unsigned char *buffer, size_t buffer_len), void *CB_DATA) This is similar to 'assuan_inquire' but the caller has to provide the outer loop (using 'assuan_process_next'). The caller should specify a continuation with CB, which receives CB_DATA as its first argument, and the error value as well as the inquired data as its remaining arguments.  File: assuan.info, Node: Utilities, Next: Socket wrappers, Prev: External I/O Loop, Up: Top 9 Utility functions ******************* There are a lot of helper functions to make writing Assuan code easier. Some of these functions provide information not available with the general functions. -- Function: gpg_error_t assuan_write_status (assuan_context_t CTX, const char *KEYWORD, const char *TEXT) This is a convenience function for a server to send a status line. You need to pass it the KEYWORD and the content of the status line in TEXT. -- Function: gpg_error_t assuan_inquire (assuan_context_t CTX, const char *KEYWORD, unsigned char **R_BUFFER, size_t *R_LENGTH, size_t MAXLEN) A server may use this function to request specific data from a client. This function sends an 'INQUIRE' command back to the client and returns the client's response in a newly allocated buffer. You need to pass at least the server's context (CTX) and a description of the required data (KEYWORD). All other parameters may be 'NULL' or '0', but this is rarely useful. On success the result is stored in a newly allocated buffer stored at R_BUFFER. The length of the data is stored at R_LENGTH. If MAXLEN has not been given as '0', it specifies an upper size limit of the expected data. If the client returns too much data the function fails and an error with the error code 'GPG_ERR_ASS_TOO_MUCH_DATA' will be returned. -- Function: FILE* assuan_get_data_fp (assuan_context_t CTX) Return a stdio stream for the Assuan context CTX. This stream may then be used for data output (assuan_write_data). The stream is valid until the end of the current handler. Calling 'fclose' for that stream is not required. Assuan does all the buffering needed to insert the status line as well as the required line wrapping and quoting for data lines. This function is only available on systems supporting either 'funopen' or 'fopencookie'. If it is not supported 'NULL' is returned and 'errno' is set to 'ENOSYS'. -- Function: gpg_error_t assuan_set_okay_line (assuan_context_t CTX, const char *LINE) Set the text used for the next 'OK' response to LINE. This is sometimes useful to send additional human readable information along with the OK line. The string is automatically reset at the end of the current handler. -- Function: gpg_error_t assuan_command_parse_fd (assuan_context_t CTX, char *LINE, assuan_fd_t *RFD) This is the core of the default 'INPUT' and 'OUTPUT' handler. It may be used in custom commands as well to negotiate a file descriptor. If LINE contains 'FD=N', it returns N in RFD assuming a local file descriptor. If LINE contains just 'FD' it returns a file descriptor at RFD; this file descriptor needs to have been sent by the client right before using 'assuan_sendfd'. On W32 systems the returned file descriptor is a system handle and not a libc low level I/O file descriptor. Thus applications need to use '_open_osfhandle' before they can pass this descriptor to standard functions like 'fdopen' or 'dup'. -- Function: const char * assuan_get_command_name (assuan_context_t CTX) Return the name of the command currently processed by a handler. The returned string is valid until the next call to an Assuan function on the same context. Returns 'NULL' if no handler is executed or the command is not known. -- Function: assuan_fd_t assuan_get_input_fd (assuan_context_t CTX) Return the file descriptor sent by the client using the last 'INPUT' command. Returns 'ASSUAN_INVALID_FD' if no file descriptor is available. -- Function: assuan_fd_t assuan_get_output_fd (assuan_context_t CTX) Return the file descriptor sent by the client using the last 'OUTPUT' command. Returns 'ASSUAN_INVALID_FD' if no file descriptor is available. -- Function: gpg_error_t assuan_close_input_fd (assuan_context_t CTX) Close the file descriptor set by the last 'INPUT' command. This function has the advantage over a simple 'close' that it can do some sanity checks and make sure that a following 'assuan_get_input_fd' won't return an already closed descriptor. -- Function: gpg_error_t assuan_close_output_fd (assuan_context_t CTX) Close the file descriptor set by the last 'OUTPUT' command. This function has the advantage over a simple 'close' that it can do some sanity checks and make sure that a following 'assuan_get_input_fd' won't return an already closed descriptor. -- Function: gpg_error_t assuan_set_error (assuan_context_t CTX, gpg_error_t ERR, const char *TEXT) This is a helper to provide a more descriptive error text with 'ERR' lines. For this to work, the text needs to be stored in the context CTX while still being in the command handler. This function is commonly called this way return assuan_set_error (ctx, err, "commands needs 5 arguments"); The value ERR is passed through and thus the return value of the command handler in the example. The provided text further explains that error to humans. -- Function: pid_t assuan_get_pid (assuan_context_t CTX) This function returns the pid of the connected connected peer. If that pid is not known 'ASSUAN_INVALID_PID' is returned. Note that it is not always possible to learn the pid of the other process. For a pipe based server the client knows it instantly and a mechanism is in place to let the server learn it. For socket based servers the pid is only available on systems providing the 'SO_PEERCRED' socket option (1). -- Data type: assuan_peercred_t This structure is used to store the peer credentials. The available members depend on the operating system. 'pid_t pid' The process ID of the peer. 'uid_t uid' The user ID of the peer process. 'gid_t gid' The group ID of the peer process. -- Function: gpg_error_t assuan_get_peercred (assuan_context_t CTX, assuan_peercred_t *PEERCRED) Return user credentials of the peer. This will work only on certain systems and only when connected over a socket. On success, a pointer to the peer credentials is stored in PEERCRED. The information is only valid as long as the state of the connection is unchanged (at least until the next assuan call to the same context). As of now only the server is able to retrieve this information. Note, that for getting the pid of the peer 'assuan_get_pid' is usually better suited. -- Function: int assuan_get_active_fds (assuan_context_t CTX, int WHAT, assuan_fd_t *FDARRAY, int FDARRAYSIZE) Return all active file descriptors for the context CTX. This function can be used to select on the file descriptors and to call 'assuan_process_next' if there is an active one. The first descriptor in the array is the one used for the command connection. Currently WHAT needs to be '0' to return descriptors used for reading, '1' will eventually be used to return descriptors used for writing. FDARRAY is an array of integers provided by the caller; FDARRAYSIZE gives the size of that array. On success the number of active descriptors are returned. These active descriptors are then stored in FDARRAY. On error '-1' is returned; the most likely reason for this is a too small FDARRAY. Note that on W32 systems the returned file descriptor is a system handle and not a libc low level I/O file descriptor. -- Function: int assuan_pending_line (assuan_context_t CTX) A call to this function return true if a full line has been buffered and thus an entire assuan line may be read without triggering any actual I/O. ---------- Footnotes ---------- (1) to our knowledge only the Linux kernel has this feature  File: assuan.info, Node: Socket wrappers, Next: Library Copying, Prev: Utilities, Up: Top 10 Socket wrapper functions *************************** It is sometimes useful to support Unix domain sockets on Windows. To do this in a portable way, Assuan provides a set of wrapper functions which may be used on any system but will enhance Windows to support these socket types. The actual implementation is based on local TCP sockets and fully transparent for the client. Server code needs to utilize two extra functions to check the permissions. -- Function: gpg_error_t assuan_sock_init (void) Initialize the socket wrappers. Must be called once at startup if any of the socket wrapper functions are used. -- Function: gpg_error_t assuan_sock_deinit (void) Deinitialize the socket wrappers. -- Function: int assuan_sock_close (assuan_fd_t FD) Wrapper for close which does a closesocket on Windows if needed. -- Function: assuan_fd_t assuan_sock_new (int DOMAIN, int TYPE, int PROTO); Wrapper around socket. -- Function: int assuan_sock_connect (assuan_fd_t SOCKFD, struct sockaddr *ADDR, int ADDRLEN) Wrapper around connect. For Unix domain sockets under Windows this function also does a write immediately after the the connect to send the nonce as read from the socket's file. Under Unix this function check whether the socket file is a redirection file and connects to the redirected socket instead; see 'assuan_sock_set_sockaddr_un' for details on the redirection file format. -- Function: int assuan_sock_connect_byname (const char * HOST, unsigned short PORT, int RESERVED, const char *CREDENTIALS, unsigned int FLAGS) Directly connect to PORT on HOST given as a name. The current implementation requires that FLAGS has either 'ASSUAN_SOCK_SOCKS' or 'ASSUAN_SOCK_TOR' set. On success a new TCP STREAM socket is returned; on error 'ASSUAN_INVALID_FD' and ERRNO set. If CREDENTIALS is not 'NULL', it is a string used for password based SOCKS authentication. Username and password are separated by a colon. RESERVED should be 0. To test whether the proxy is available HOST and PORT may be given as NULL/0: If the proxy is available the function returns a valid socket which is in the state after credentials sub-negotiation. The caller now knows that the SOCKS proxy is available and has been authenticated; normally the caller closes the socket then. -- Function: int assuan_sock_bind ( assuan_fd_t SOCKFD, struct sockaddr *ADDR, int ADDRLEN) Wrapper around bind. Under Windows this creates a file and writes the port number and a random nonce to this file. -- Function: int assuan_sock_set_sockaddr_un ( const char *FNAME, struct sockaddr *ADDR, int *R_REDIRECTED) This is a helper function to initialize the Unix socket domain address structure ADDR and store the file name FNAME there. If R_REDIRECTED is not NULL the function checks whether FNAME already exists, is a regular file, and not a socket. In that case FNAME is read to see whether this is a redirection to a socket file. If that is the case 1 is stored at R_REDIRECTED. If the file does not look like a redirection file 0 will be stored there and FNAME will be used in the regular way. The format of a redirection file is %Assuan% socket=NAME With NAME being is the actual socket to use. No white spaces are allowed, both lines must be terminated by a single linefeed, and extra lines are not allowed. Environment variables are interpreted in NAME if given in '${VAR}' notation. No escape characters are defined; if the string '${' shall be used in file name, an environment variable with that content may be used. The length of the redirection file is limited to 511 bytes which is more than sufficient for any known implementation of Unix domain sockets. -- Function: int assuan_sock_get_nonce ( struct sockaddr *ADDR, int ADDRLEN, assuan_sock_nonce_t *NONCE) This is used by the server after a bind to return the random nonce. To keep the code readable this may also be used on POSIX system. -- Function: int assuan_sock_check_nonce ( assuan_fd_t FD, assuan_sock_nonce_t *NONCE) If the option 'ASSUAN_SOCKET_SERVER_ACCEPTED' has been used, Libassuan has no way to check the nonce of the server. Thus an explicit check of the saved nonce using this function is required. If this function fails the server should immediately drop the connection. This function may not be used if Libassuan does the accept call itself (i.e. 'ASSUAN_SOCKET_SERVER_ACCEPTED' has not been used) because in this case Libassuan calls this function internally. See also 'assuan_set_sock_nonce'. Actually this mechanism is only required on Windows but for cleanness of code it may be used on POSIX systems as well, where this function is a nop. To control certain properties of the wrapper two additional functions are provided: -- Function: int assuan_sock_set_flag ( assuan_fd_t FD, const char *NAME, int VALUE) Set the flags NAME for socket FD to VALUE. See below for a list of valid names. Returns 0 on success; on failure sets ERRNO and returns -1. -- Function: int assuan_sock_get_flag ( assuan_fd_t FD, const char *NAME, int *R_VALUE) Store the current value of the flag NAME for socket FD at R_VALUE. See below for a list of valid names. Returns 0 on success; on failure sets ERRNO and returns -1. The supported flags are: 'cygwin' This flag has an effect only on Windows. If the value is 1, the socket is set into Cygwin mode so that Cygwin clients can connect to such a socket. This flag needs to be set before a bind and should not be changed during the lifetime of the socket. There is no need to set this flag for connecting to a Cygwin style socket because no state is required at the client. On non-Windows platforms setting this flag is ignored, reading the flag always returns a value of 0. 'tor-mode' 'socks' If VALUE is 1 globally enable SOCKS5 mode for new connections using IPv6 or IPv4. FD must be set to 'ASSUAN_INVALID_FD' A future extension may allow to disable SOCKS5 mode for a specified socket but globally disabling SOCKS5 mode is not possible. Using the flag "tor-mode" expects the SOCKS5 proxy to listen on port 9050, the flag "socks" expects the proxy to listen on port 1080. Connections to the loopback address are not routed though the SOCKS proxy. UDP requests are not supported at all. The proxy will be connected at address 127.0.0.1; an IPv6 connection to the proxy is not yet supported.  File: assuan.info, Node: Library Copying, Next: Copying, Prev: Socket wrappers, Up: Top GNU Lesser General Public License ********************************* Version 2.1, February 1999 Copyright (C) 1991, 1999 Free Software Foundation, Inc. 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. [This is the first released version of the Lesser GPL. It also counts as the successor of the GNU Library Public License, version 2, hence the version number 2.1.] Preamble ======== The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public Licenses are intended to guarantee your freedom to share and change free software--to make sure the software is free for all its users. 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IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE LIBRARY AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE LIBRARY (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE LIBRARY TO OPERATE WITH ANY OTHER SOFTWARE), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. END OF TERMS AND CONDITIONS How to Apply These Terms to Your New Libraries ============================================== If you develop a new library, and you want it to be of the greatest possible use to the public, we recommend making it free software that everyone can redistribute and change. You can do so by permitting redistribution under these terms (or, alternatively, under the terms of the ordinary General Public License). To apply these terms, attach the following notices to the library. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the "copyright" line and a pointer to where the full notice is found. ONE LINE TO GIVE THE LIBRARY'S NAME AND AN IDEA OF WHAT IT DOES. Copyright (C) YEAR NAME OF AUTHOR This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA. Also add information on how to contact you by electronic and paper mail. You should also get your employer (if you work as a programmer) or your school, if any, to sign a "copyright disclaimer" for the library, if necessary. Here is a sample; alter the names: Yoyodyne, Inc., hereby disclaims all copyright interest in the library `Frob' (a library for tweaking knobs) written by James Random Hacker. SIGNATURE OF TY COON, 1 April 1990 Ty Coon, President of Vice That's all there is to it!  File: assuan.info, Node: Copying, Next: Index, Prev: Library Copying, Up: Top GNU General Public License ************************** Version 3, 29 June 2007 Copyright (C) 2007 Free Software Foundation, Inc. Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. Preamble ======== The GNU General Public License is a free, copyleft license for software and other kinds of works. The licenses for most software and other practical works are designed to take away your freedom to share and change the works. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change all versions of a program-to make sure it remains free software for all its users. We, the Free Software Foundation, use the GNU General Public License for most of our software; it applies also to any other work released this way by its authors. You can apply it to your programs, too. When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for them if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs, and that you know you can do these things. To protect your rights, we need to prevent others from denying you these rights or asking you to surrender the rights. Therefore, you have certain responsibilities if you distribute copies of the software, or if you modify it: responsibilities to respect the freedom of others. For example, if you distribute copies of such a program, whether gratis or for a fee, you must pass on to the recipients the same freedoms that you received. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights. Developers that use the GNU GPL protect your rights with two steps: (1) assert copyright on the software, and (2) offer you this License giving you legal permission to copy, distribute and/or modify it. For the developers' and authors' protection, the GPL clearly explains that there is no warranty for this free software. For both users' and authors' sake, the GPL requires that modified versions be marked as changed, so that their problems will not be attributed erroneously to authors of previous versions. Some devices are designed to deny users access to install or run modified versions of the software inside them, although the manufacturer can do so. This is fundamentally incompatible with the aim of protecting users' freedom to change the software. The systematic pattern of such abuse occurs in the area of products for individuals to use, which is precisely where it is most unacceptable. Therefore, we have designed this version of the GPL to prohibit the practice for those products. If such problems arise substantially in other domains, we stand ready to extend this provision to those domains in future versions of the GPL, as needed to protect the freedom of users. Finally, every program is threatened constantly by software patents. States should not allow patents to restrict development and use of software on general-purpose computers, but in those that do, we wish to avoid the special danger that patents applied to a free program could make it effectively proprietary. To prevent this, the GPL assures that patents cannot be used to render the program non-free. The precise terms and conditions for copying, distribution and modification follow. TERMS AND CONDITIONS 0. Definitions. "This License" refers to version 3 of the GNU General Public License. "Copyright" also means copyright-like laws that apply to other kinds of works, such as semiconductor masks. "The Program" refers to any copyrightable work licensed under this License. Each licensee is addressed as "you". "Licensees" and "recipients" may be individuals or organizations. To "modify" a work means to copy from or adapt all or part of the work in a fashion requiring copyright permission, other than the making of an exact copy. The resulting work is called a "modified version" of the earlier work or a work "based on" the earlier work. A "covered work" means either the unmodified Program or a work based on the Program. To "propagate" a work means to do anything with it that, without permission, would make you directly or secondarily liable for infringement under applicable copyright law, except executing it on a computer or modifying a private copy. Propagation includes copying, distribution (with or without modification), making available to the public, and in some countries other activities as well. To "convey" a work means any kind of propagation that enables other parties to make or receive copies. Mere interaction with a user through a computer network, with no transfer of a copy, is not conveying. An interactive user interface displays "Appropriate Legal Notices" to the extent that it includes a convenient and prominently visible feature that (1) displays an appropriate copyright notice, and (2) tells the user that there is no warranty for the work (except to the extent that warranties are provided), that licensees may convey the work under this License, and how to view a copy of this License. If the interface presents a list of user commands or options, such as a menu, a prominent item in the list meets this criterion. 1. Source Code. The "source code" for a work means the preferred form of the work for making modifications to it. "Object code" means any non-source form of a work. 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The Corresponding Source for a work in source code form is that same work. 2. Basic Permissions. All rights granted under this License are granted for the term of copyright on the Program, and are irrevocable provided the stated conditions are met. This License explicitly affirms your unlimited permission to run the unmodified Program. The output from running a covered work is covered by this License only if the output, given its content, constitutes a covered work. This License acknowledges your rights of fair use or other equivalent, as provided by copyright law. You may make, run and propagate covered works that you do not convey, without conditions so long as your license otherwise remains in force. You may convey covered works to others for the sole purpose of having them make modifications exclusively for you, or provide you with facilities for running those works, provided that you comply with the terms of this License in conveying all material for which you do not control copyright. Those thus making or running the covered works for you must do so exclusively on your behalf, under your direction and control, on terms that prohibit them from making any copies of your copyrighted material outside their relationship with you. Conveying under any other circumstances is permitted solely under the conditions stated below. Sublicensing is not allowed; section 10 makes it unnecessary. 3. Protecting Users' Legal Rights From Anti-Circumvention Law. 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Regardless of what server hosts the Corresponding Source, you remain obligated to ensure that it is available for as long as needed to satisfy these requirements. e. Convey the object code using peer-to-peer transmission, provided you inform other peers where the object code and Corresponding Source of the work are being offered to the general public at no charge under subsection 6d. A separable portion of the object code, whose source code is excluded from the Corresponding Source as a System Library, need not be included in conveying the object code work. A "User Product" is either (1) a "consumer product", which means any tangible personal property which is normally used for personal, family, or household purposes, or (2) anything designed or sold for incorporation into a dwelling. In determining whether a product is a consumer product, doubtful cases shall be resolved in favor of coverage. 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If additional permissions apply only to part of the Program, that part may be used separately under those permissions, but the entire Program remains governed by this License without regard to the additional permissions. When you convey a copy of a covered work, you may at your option remove any additional permissions from that copy, or from any part of it. (Additional permissions may be written to require their own removal in certain cases when you modify the work.) You may place additional permissions on material, added by you to a covered work, for which you have or can give appropriate copyright permission. Notwithstanding any other provision of this License, for material you add to a covered work, you may (if authorized by the copyright holders of that material) supplement the terms of this License with terms: a. Disclaiming warranty or limiting liability differently from the terms of sections 15 and 16 of this License; or b. 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If the Program as you received it, or any part of it, contains a notice stating that it is governed by this License along with a term that is a further restriction, you may remove that term. If a license document contains a further restriction but permits relicensing or conveying under this License, you may add to a covered work material governed by the terms of that license document, provided that the further restriction does not survive such relicensing or conveying. If you add terms to a covered work in accord with this section, you must place, in the relevant source files, a statement of the additional terms that apply to those files, or a notice indicating where to find the applicable terms. Additional terms, permissive or non-permissive, may be stated in the form of a separately written license, or stated as exceptions; the above requirements apply either way. 8. Termination. You may not propagate or modify a covered work except as expressly provided under this License. Any attempt otherwise to propagate or modify it is void, and will automatically terminate your rights under this License (including any patent licenses granted under the third paragraph of section 11). However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation. Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice. Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, you do not qualify to receive new licenses for the same material under section 10. 9. Acceptance Not Required for Having Copies. You are not required to accept this License in order to receive or run a copy of the Program. Ancillary propagation of a covered work occurring solely as a consequence of using peer-to-peer transmission to receive a copy likewise does not require acceptance. However, nothing other than this License grants you permission to propagate or modify any covered work. These actions infringe copyright if you do not accept this License. Therefore, by modifying or propagating a covered work, you indicate your acceptance of this License to do so. 10. Automatic Licensing of Downstream Recipients. Each time you convey a covered work, the recipient automatically receives a license from the original licensors, to run, modify and propagate that work, subject to this License. You are not responsible for enforcing compliance by third parties with this License. An "entity transaction" is a transaction transferring control of an organization, or substantially all assets of one, or subdividing an organization, or merging organizations. If propagation of a covered work results from an entity transaction, each party to that transaction who receives a copy of the work also receives whatever licenses to the work the party's predecessor in interest had or could give under the previous paragraph, plus a right to possession of the Corresponding Source of the work from the predecessor in interest, if the predecessor has it or can get it with reasonable efforts. You may not impose any further restrictions on the exercise of the rights granted or affirmed under this License. For example, you may not impose a license fee, royalty, or other charge for exercise of rights granted under this License, and you may not initiate litigation (including a cross-claim or counterclaim in a lawsuit) alleging that any patent claim is infringed by making, using, selling, offering for sale, or importing the Program or any portion of it. 11. Patents. A "contributor" is a copyright holder who authorizes use under this License of the Program or a work on which the Program is based. The work thus licensed is called the contributor's "contributor version". A contributor's "essential patent claims" are all patent claims owned or controlled by the contributor, whether already acquired or hereafter acquired, that would be infringed by some manner, permitted by this License, of making, using, or selling its contributor version, but do not include claims that would be infringed only as a consequence of further modification of the contributor version. For purposes of this definition, "control" includes the right to grant patent sublicenses in a manner consistent with the requirements of this License. Each contributor grants you a non-exclusive, worldwide, royalty-free patent license under the contributor's essential patent claims, to make, use, sell, offer for sale, import and otherwise run, modify and propagate the contents of its contributor version. In the following three paragraphs, a "patent license" is any express agreement or commitment, however denominated, not to enforce a patent (such as an express permission to practice a patent or covenant not to sue for patent infringement). To "grant" such a patent license to a party means to make such an agreement or commitment not to enforce a patent against the party. If you convey a covered work, knowingly relying on a patent license, and the Corresponding Source of the work is not available for anyone to copy, free of charge and under the terms of this License, through a publicly available network server or other readily accessible means, then you must either (1) cause the Corresponding Source to be so available, or (2) arrange to deprive yourself of the benefit of the patent license for this particular work, or (3) arrange, in a manner consistent with the requirements of this License, to extend the patent license to downstream recipients. "Knowingly relying" means you have actual knowledge that, but for the patent license, your conveying the covered work in a country, or your recipient's use of the covered work in a country, would infringe one or more identifiable patents in that country that you have reason to believe are valid. If, pursuant to or in connection with a single transaction or arrangement, you convey, or propagate by procuring conveyance of, a covered work, and grant a patent license to some of the parties receiving the covered work authorizing them to use, propagate, modify or convey a specific copy of the covered work, then the patent license you grant is automatically extended to all recipients of the covered work and works based on it. A patent license is "discriminatory" if it does not include within the scope of its coverage, prohibits the exercise of, or is conditioned on the non-exercise of one or more of the rights that are specifically granted under this License. You may not convey a covered work if you are a party to an arrangement with a third party that is in the business of distributing software, under which you make payment to the third party based on the extent of your activity of conveying the work, and under which the third party grants, to any of the parties who would receive the covered work from you, a discriminatory patent license (a) in connection with copies of the covered work conveyed by you (or copies made from those copies), or (b) primarily for and in connection with specific products or compilations that contain the covered work, unless you entered into that arrangement, or that patent license was granted, prior to 28 March 2007. Nothing in this License shall be construed as excluding or limiting any implied license or other defenses to infringement that may otherwise be available to you under applicable patent law. 12. No Surrender of Others' Freedom. If conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License. If you cannot convey a covered work so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not convey it at all. For example, if you agree to terms that obligate you to collect a royalty for further conveying from those to whom you convey the Program, the only way you could satisfy both those terms and this License would be to refrain entirely from conveying the Program. 13. Use with the GNU Affero General Public License. Notwithstanding any other provision of this License, you have permission to link or combine any covered work with a work licensed under version 3 of the GNU Affero General Public License into a single combined work, and to convey the resulting work. The terms of this License will continue to apply to the part which is the covered work, but the special requirements of the GNU Affero General Public License, section 13, concerning interaction through a network will apply to the combination as such. 14. Revised Versions of this License. The Free Software Foundation may publish revised and/or new versions of the GNU General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. Each version is given a distinguishing version number. If the Program specifies that a certain numbered version of the GNU General Public License "or any later version" applies to it, you have the option of following the terms and conditions either of that numbered version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of the GNU General Public License, you may choose any version ever published by the Free Software Foundation. If the Program specifies that a proxy can decide which future versions of the GNU General Public License can be used, that proxy's public statement of acceptance of a version permanently authorizes you to choose that version for the Program. Later license versions may give you additional or different permissions. However, no additional obligations are imposed on any author or copyright holder as a result of your choosing to follow a later version. 15. Disclaimer of Warranty. THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION. 16. Limitation of Liability. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. 17. Interpretation of Sections 15 and 16. If the disclaimer of warranty and limitation of liability provided above cannot be given local legal effect according to their terms, reviewing courts shall apply local law that most closely approximates an absolute waiver of all civil liability in connection with the Program, unless a warranty or assumption of liability accompanies a copy of the Program in return for a fee. END OF TERMS AND CONDITIONS How to Apply These Terms to Your New Programs ============================================= If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms. To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively state the exclusion of warranty; and each file should have at least the "copyright" line and a pointer to where the full notice is found. ONE LINE TO GIVE THE PROGRAM'S NAME AND A BRIEF IDEA OF WHAT IT DOES. Copyright (C) YEAR NAME OF AUTHOR This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see . Also add information on how to contact you by electronic and paper mail. If the program does terminal interaction, make it output a short notice like this when it starts in an interactive mode: PROGRAM Copyright (C) YEAR NAME OF AUTHOR This program comes with ABSOLUTELY NO WARRANTY; for details type 'show w'. This is free software, and you are welcome to redistribute it under certain conditions; type 'show c' for details. The hypothetical commands 'show w' and 'show c' should show the appropriate parts of the General Public License. Of course, your program's commands might be different; for a GUI interface, you would use an "about box". You should also get your employer (if you work as a programmer) or school, if any, to sign a "copyright disclaimer" for the program, if necessary. For more information on this, and how to apply and follow the GNU GPL, see . The GNU General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Lesser General Public License instead of this License. But first, please read .  File: assuan.info, Node: Index, Prev: Copying, Up: Top Index ***** [index] * Menu: * AM_PATH_LIBASSUAN: Automake. (line 11) * assuan_accept: Server code. (line 267) * assuan_begin_confidential: Contexts. (line 110) * assuan_close_input_fd: Utilities. (line 93) * assuan_close_output_fd: Utilities. (line 100) * assuan_command_parse_fd: Utilities. (line 57) * assuan_context_t: Data Types. (line 9) * assuan_ctx_set_system_hooks: Contexts. (line 222) * assuan_end_confidential: Contexts. (line 117) * assuan_fdopen: Data Types. (line 21) * assuan_fd_t: Data Types. (line 16) * assuan_flag_t: Contexts. (line 81) * assuan_get_active_fds: Utilities. (line 154) * assuan_get_assuan_log_prefix: Default Log Handler. (line 12) * assuan_get_assuan_log_stream: Default Log Handler. (line 26) * assuan_get_command_name: Utilities. (line 73) * assuan_get_data_fp: Utilities. (line 36) * assuan_get_flag: Contexts. (line 105) * assuan_get_gpg_err_source: Initializing the library. (line 72) * assuan_get_input_fd: Utilities. (line 81) * assuan_get_log_cb: Initializing the library. (line 112) * assuan_get_malloc_hooks: Initializing the library. (line 54) * assuan_get_output_fd: Utilities. (line 87) * assuan_get_peercred: Utilities. (line 141) * assuan_get_pid: Utilities. (line 118) * assuan_get_pointer: Contexts. (line 61) * assuan_init_pipe_server: Server code. (line 74) * assuan_init_socket_server: Server code. (line 90) * assuan_inquire: Utilities. (line 17) * assuan_inquire_ext: External I/O Loop Server. (line 80) * assuan_malloc_hooks_t: Initializing the library. (line 41) * assuan_new: Contexts. (line 13) * assuan_new_ext: Contexts. (line 33) * assuan_peercred_t: Utilities. (line 128) * assuan_pending_line: Utilities. (line 174) * assuan_pipe_connect: Client code. (line 12) * assuan_process: Server code. (line 277) * assuan_process_done: External I/O Loop Server. (line 75) * assuan_process_next: External I/O Loop Server. (line 69) * assuan_read_line: Reading and Writing. (line 12) * assuan_receivefd: Client code. (line 127) * assuan_register_bye_notify: Server code. (line 170) * assuan_register_cancel_notify: Server code. (line 183) * assuan_register_command: Server code. (line 142) * assuan_register_input_notify: Server code. (line 202) * assuan_register_option_handler: Server code. (line 189) * assuan_register_output_notify: Server code. (line 215) * assuan_register_post_cmd_notify: Server code. (line 161) * assuan_register_reset_notify: Server code. (line 177) * assuan_release: Contexts. (line 45) * assuan_sendfd: Client code. (line 114) * assuan_send_data: Reading and Writing. (line 35) * assuan_set_assuan_log_prefix: Default Log Handler. (line 8) * assuan_set_assuan_log_stream: Default Log Handler. (line 17) * assuan_set_error: Utilities. (line 107) * assuan_set_flag: Contexts. (line 74) * assuan_set_gpg_err_source: Initializing the library. (line 63) * assuan_set_hello_line: Server code. (line 228) * assuan_set_io_monitor: Reading and Writing. (line 72) * assuan_set_log_cb: Initializing the library. (line 106) * assuan_set_log_stream: Default Log Handler. (line 33) * assuan_set_malloc_hooks: Initializing the library. (line 44) * assuan_set_okay_line: Utilities. (line 49) * assuan_set_pointer: Contexts. (line 53) * assuan_set_sock_nonce: Server code. (line 112) * assuan_set_system_hooks: Contexts. (line 207) * assuan_socket_connect: Client code. (line 55) * assuan_sock_bind: Socket wrappers. (line 56) * assuan_sock_check_nonce: Socket wrappers. (line 95) * assuan_sock_close: Socket wrappers. (line 20) * assuan_sock_connect: Socket wrappers. (line 28) * assuan_sock_connect_byname: Socket wrappers. (line 39) * assuan_sock_deinit: Socket wrappers. (line 17) * assuan_sock_get_flag: Socket wrappers. (line 122) * assuan_sock_get_nonce: Socket wrappers. (line 88) * assuan_sock_init: Socket wrappers. (line 13) * assuan_sock_new: Socket wrappers. (line 23) * assuan_sock_set_flag: Socket wrappers. (line 114) * assuan_sock_set_sockaddr_un: Socket wrappers. (line 62) * assuan_sock_set_system_hooks: Contexts. (line 213) * assuan_transact: Client code. (line 72) * assuan_write_line: Reading and Writing. (line 23) * assuan_write_status: Utilities. (line 10) * gpg_error_t (*assuan_handler_t) (assuan_context_t CTX, char *LINE): Server code. (line 136) * int (*assuan_log_cb_t) (assuan_context_t CTX, void *HOOK_VALUE, unsigned int CAT, const char *MSG): Initializing the library. (line 79) * introduction: Top. (line 6) * LGPL, GNU Lesser General Public License: Library Copying. (line 6) * struct assuan_malloc_hooks: Initializing the library. (line 24) * struct assuan_system_hooks: Contexts. (line 124) * unsigned int (*assuan_io_monitor_t) (assuan_context_t CTX, void *HOOK_VALUE, int INOUT, const char *LINE, size_t LINELEN): Reading and Writing. (line 54)  Tag Table: Node: Top907 Node: Introduction1973 Node: Assuan4228 Node: Implementation5272 Node: Server responses6451 Node: Client requests8741 Node: Error codes11779 Node: Preparation12118 Node: Header12693 Node: Building sources13479 Node: Automake15378 Node: Multi Threading16526 Node: Generalities17485 Node: Data Types17889 Node: Initializing the library18997 Ref: function assuan_set_gpg_err_source21693 Node: Default Log Handler24012 Node: Contexts25778 Ref: function assuan_new26358 Node: Reading and Writing36930 Node: Client code40405 Ref: function assuan_sendfd45402 Ref: function assuan_receivefd45993 Node: Server code46368 Node: External I/O Loop58493 Node: External I/O Loop Client60318 Node: External I/O Loop Server63403 Node: Utilities67987 Ref: Utilities-Footnote-176088 Node: Socket wrappers76152 Node: Library Copying83133 Node: Copying111245 Node: Index148759  End Tag Table