@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
-@c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc.
+@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2002, 2003,
+@c 2004, 2005, 2006 Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@setfilename ../info/processes
-@node Processes, System Interface, Abbrevs, Top
+@node Processes, Display, Abbrevs, Top
@chapter Processes
@cindex child process
@cindex parent process
@menu
* Subprocess Creation:: Functions that start subprocesses.
+* Shell Arguments:: Quoting an argument to pass it to a shell.
* Synchronous Processes:: Details of using synchronous subprocesses.
* Asynchronous Processes:: Starting up an asynchronous subprocess.
* Deleting Processes:: Eliminating an asynchronous subprocess.
an asynchronous subprocess.
* Output from Processes:: Collecting output from an asynchronous subprocess.
* Sentinels:: Sentinels run when process run-status changes.
+* Query Before Exit:: Whether to query if exiting will kill a process.
* Transaction Queues:: Transaction-based communication with subprocesses.
-* TCP:: Opening network connections.
+* Network:: Opening network connections.
+* Network Servers:: Network servers let Emacs accept net connections.
+* Datagrams:: UDP network connections.
+* Low-Level Network:: Lower-level but more general function
+ to create connections and servers.
+* Misc Network:: Additional relevant functions for network connections.
+* Byte Packing:: Using bindat to pack and unpack binary data.
@end menu
@node Subprocess Creation
create a synchronous process and do not return a process object
(@pxref{Synchronous Processes}).
- Synchronous and asynchronous processes are explained in following
+ Synchronous and asynchronous processes are explained in the following
sections. Since the three functions are all called in a similar
fashion, their common arguments are described here.
@code{exec-path} contains a list of directories to search. Emacs
initializes @code{exec-path} when it starts up, based on the value of
the environment variable @code{PATH}. The standard file name
-constructs, @samp{~}, @samp{.}, and @samp{..}, are interpreted as usual
-in @code{exec-path}, but environment variable substitutions
+constructs, @samp{~}, @samp{.}, and @samp{..}, are interpreted as
+usual in @code{exec-path}, but environment variable substitutions
(@samp{$HOME}, etc.) are not recognized; use
@code{substitute-in-file-name} to perform them (@pxref{File Name
-Expansion}).
+Expansion}). @code{nil} in this list refers to
+@code{default-directory}.
+
+ Executing a program can also try adding suffixes to the specified
+name:
+
+@defvar exec-suffixes
+This variable is a list of suffixes (strings) to try adding to the
+specified program file name. The list should include @code{""} if you
+want the name to be tried exactly as specified. The default value is
+system-dependent.
+@end defvar
+
+ @strong{Please note:} The argument @var{program} contains only the
+name of the program; it may not contain any command-line arguments. You
+must use @var{args} to provide those.
Each of the subprocess-creating functions has a @var{buffer-or-name}
argument which specifies where the standard output from the program will
-go. If @var{buffer-or-name} is @code{nil}, that says to discard the
-output unless a filter function handles it. (@xref{Filter Functions},
-and @ref{Streams}.) Normally, you should avoid having multiple
-processes send output to the same buffer because their output would be
-intermixed randomly.
+go. It should be a buffer or a buffer name; if it is a buffer name,
+that will create the buffer if it does not already exist. It can also
+be @code{nil}, which says to discard the output unless a filter function
+handles it. (@xref{Filter Functions}, and @ref{Read and Print}.)
+Normally, you should avoid having multiple processes send output to the
+same buffer because their output would be intermixed randomly.
@cindex program arguments
All three of the subprocess-creating functions have a @code{&rest}
argument, @var{args}. The @var{args} must all be strings, and they are
supplied to @var{program} as separate command line arguments. Wildcard
-characters and other shell constructs are not allowed in these strings,
-since they are passed directly to the specified program.
-
- @strong{Please note:} the argument @var{program} contains only the
-name of the program; it may not contain any command-line arguments. You
-must use @var{args} to provide those.
+characters and other shell constructs have no special meanings in these
+strings, since the strings are passed directly to the specified program.
The subprocess gets its current directory from the value of
@code{default-directory} (@pxref{File Name Expansion}).
@cindex environment variables, subprocesses
- The subprocess inherits its environment from Emacs; but you can
+ The subprocess inherits its environment from Emacs, but you can
specify overrides for it with @code{process-environment}. @xref{System
Environment}.
-@defvar exec-directory
-@pindex wakeup
-The value of this variable is the name of a directory (a string) that
-contains programs that come with GNU Emacs, that are intended for Emacs
-to invoke. The program @code{wakeup} is an example of such a program;
-the @code{display-time} command uses it to get a reminder once per
-minute.
+@defvar exec-directory
+@pindex movemail
+The value of this variable is a string, the name of a directory that
+contains programs that come with GNU Emacs, programs intended for Emacs
+to invoke. The program @code{movemail} is an example of such a program;
+Rmail uses it to fetch new mail from an inbox.
@end defvar
@defopt exec-path
file name.
@end defopt
+@node Shell Arguments
+@section Shell Arguments
+
+ Lisp programs sometimes need to run a shell and give it a command
+that contains file names that were specified by the user. These
+programs ought to be able to support any valid file name. But the shell
+gives special treatment to certain characters, and if these characters
+occur in the file name, they will confuse the shell. To handle these
+characters, use the function @code{shell-quote-argument}:
+
+@defun shell-quote-argument argument
+This function returns a string which represents, in shell syntax,
+an argument whose actual contents are @var{argument}. It should
+work reliably to concatenate the return value into a shell command
+and then pass it to a shell for execution.
+
+Precisely what this function does depends on your operating system. The
+function is designed to work with the syntax of your system's standard
+shell; if you use an unusual shell, you will need to redefine this
+function.
+
+@example
+;; @r{This example shows the behavior on GNU and Unix systems.}
+(shell-quote-argument "foo > bar")
+ @result{} "foo\\ \\>\\ bar"
+
+;; @r{This example shows the behavior on MS-DOS and MS-Windows.}
+(shell-quote-argument "foo > bar")
+ @result{} "\"foo > bar\""
+@end example
+
+Here's an example of using @code{shell-quote-argument} to construct
+a shell command:
+
+@example
+(concat "diff -c "
+ (shell-quote-argument oldfile)
+ " "
+ (shell-quote-argument newfile))
+@end example
+@end defun
+
@node Synchronous Processes
@section Creating a Synchronous Process
@cindex synchronous subprocess
After a @dfn{synchronous process} is created, Emacs waits for the
-process to terminate before continuing. Starting Dired is an example of
-this: it runs @code{ls} in a synchronous process, then modifies the
-output slightly. Because the process is synchronous, the entire
-directory listing arrives in the buffer before Emacs tries to do
-anything with it.
+process to terminate before continuing. Starting Dired on GNU or
+Unix@footnote{On other systems, Emacs uses a Lisp emulation of
+@code{ls}; see @ref{Contents of Directories}.} is an example of this: it
+runs @code{ls} in a synchronous process, then modifies the output
+slightly. Because the process is synchronous, the entire directory
+listing arrives in the buffer before Emacs tries to do anything with it.
While Emacs waits for the synchronous subprocess to terminate, the
user can quit by typing @kbd{C-g}. The first @kbd{C-g} tries to kill
the subprocess with a @code{SIGINT} signal; but it waits until the
subprocess actually terminates before quitting. If during that time the
user types another @kbd{C-g}, that kills the subprocess instantly with
-@code{SIGKILL} and quits immediately. @xref{Quitting}.
+@code{SIGKILL} and quits immediately (except on MS-DOS, where killing
+other processes doesn't work). @xref{Quitting}.
+
+ The synchronous subprocess functions return an indication of how the
+process terminated.
- The synchronous subprocess functions returned @code{nil} in version
-18. In version 19, they return an indication of how the process
-terminated.
+ The output from a synchronous subprocess is generally decoded using a
+coding system, much like text read from a file. The input sent to a
+subprocess by @code{call-process-region} is encoded using a coding
+system, much like text written into a file. @xref{Coding Systems}.
-@defun call-process program &optional infile buffer-or-name display &rest args
+@defun call-process program &optional infile destination display &rest args
This function calls @var{program} in a separate process and waits for
it to finish.
The standard input for the process comes from file @var{infile} if
-@var{infile} is not @code{nil} and from @file{/dev/null} otherwise. The
-process output gets inserted in buffer @var{buffer-or-name} before point,
-if that argument names a buffer. If @var{buffer-or-name} is @code{t},
-output is sent to the current buffer; if @var{buffer-or-name} is
-@code{nil}, output is discarded.
-
-If @var{buffer-or-name} is the integer 0, @code{call-process} returns
-@code{nil} immediately and discards any output. In this case, the
-process is not truly synchronous, since it can run in parallel with
-Emacs; but you can think of it as synchronous in that Emacs is
-essentially finished with the subprocess as soon as this function
-returns.
+@var{infile} is not @code{nil}, and from the null device otherwise.
+The argument @var{destination} says where to put the process output.
+Here are the possibilities:
+
+@table @asis
+@item a buffer
+Insert the output in that buffer, before point. This includes both the
+standard output stream and the standard error stream of the process.
+
+@item a string
+Insert the output in a buffer with that name, before point.
+
+@item @code{t}
+Insert the output in the current buffer, before point.
+
+@item @code{nil}
+Discard the output.
+
+@item 0
+Discard the output, and return @code{nil} immediately without waiting
+for the subprocess to finish.
+
+In this case, the process is not truly synchronous, since it can run in
+parallel with Emacs; but you can think of it as synchronous in that
+Emacs is essentially finished with the subprocess as soon as this
+function returns.
+
+MS-DOS doesn't support asynchronous subprocesses, so this option doesn't
+work there.
+
+@item @code{(@var{real-destination} @var{error-destination})}
+Keep the standard output stream separate from the standard error stream;
+deal with the ordinary output as specified by @var{real-destination},
+and dispose of the error output according to @var{error-destination}.
+If @var{error-destination} is @code{nil}, that means to discard the
+error output, @code{t} means mix it with the ordinary output, and a
+string specifies a file name to redirect error output into.
+
+You can't directly specify a buffer to put the error output in; that is
+too difficult to implement. But you can achieve this result by sending
+the error output to a temporary file and then inserting the file into a
+buffer.
+@end table
If @var{display} is non-@code{nil}, then @code{call-process} redisplays
-the buffer as output is inserted. Otherwise the function does no
-redisplay, and the results become visible on the screen only when Emacs
-redisplays that buffer in the normal course of events.
+the buffer as output is inserted. (However, if the coding system chosen
+for decoding output is @code{undecided}, meaning deduce the encoding
+from the actual data, then redisplay sometimes cannot continue once
+non-@acronym{ASCII} characters are encountered. There are fundamental
+reasons why it is hard to fix this; see @ref{Output from Processes}.)
+
+Otherwise the function @code{call-process} does no redisplay, and the
+results become visible on the screen only when Emacs redisplays that
+buffer in the normal course of events.
The remaining arguments, @var{args}, are strings that specify command
line arguments for the program.
@smallexample
@group
(call-process "pwd" nil t)
- @result{} nil
+ @result{} 0
---------- Buffer: foo ----------
/usr/user/lewis/manual
@group
(call-process "grep" nil "bar" nil "lewis" "/etc/passwd")
- @result{} nil
+ @result{} 0
---------- Buffer: bar ----------
lewis:5LTsHm66CSWKg:398:21:Bil Lewis:/user/lewis:/bin/csh
@end group
@end smallexample
-The @code{insert-directory} function contains a good example of the use
-of @code{call-process}:
+Here is a good example of the use of @code{call-process}, which used to
+be found in the definition of @code{insert-directory}:
@smallexample
@group
-(call-process insert-directory-program nil t nil switches
+(call-process insert-directory-program nil t nil @var{switches}
(if full-directory-p
(concat (file-name-as-directory file) ".")
file))
@end smallexample
@end defun
-@defun call-process-region start end program &optional delete buffer-or-name display &rest args
-This function sends the text between @var{start} to @var{end} as
+@defun process-file program &optional infile buffer display &rest args
+This function processes files synchronously in a separate process. It
+is similar to @code{call-process} but may invoke a file handler based
+on the value of the variable @code{default-directory}. The current
+working directory of the subprocess is @code{default-directory}.
+
+The arguments are handled in almost the same way as for
+@code{call-process}, with the following differences:
+
+Some file handlers may not support all combinations and forms of the
+arguments @var{infile}, @var{buffer}, and @var{display}. For example,
+some file handlers might behave as if @var{display} were @code{nil},
+regardless of the value actually passed. As another example, some
+file handlers might not support separating standard output and error
+output by way of the @var{buffer} argument.
+
+If a file handler is invoked, it determines the program to run based
+on the first argument @var{program}. For instance, consider that a
+handler for remote files is invoked. Then the path that is used for
+searching the program might be different than @code{exec-path}.
+
+The second argument @var{infile} may invoke a file handler. The file
+handler could be different from the handler chosen for the
+@code{process-file} function itself. (For example,
+@code{default-directory} could be on a remote host, whereas
+@var{infile} is on another remote host. Or @code{default-directory}
+could be non-special, whereas @var{infile} is on a remote host.)
+
+If @var{buffer} has the form @code{(@var{real-destination}
+@var{error-destination})}, and @var{error-destination} names a file,
+then the same remarks as for @var{infile} apply.
+
+The remaining arguments (@var{args}) will be passed to the process
+verbatim. Emacs is not involved in processing file names that are
+present in @var{args}. To avoid confusion, it may be best to avoid
+absolute file names in @var{args}, but rather to specify all file
+names as relative to @code{default-directory}. The function
+@code{file-relative-name} is useful for constructing such relative
+file names.
+@end defun
+
+@defun call-process-region start end program &optional delete destination display &rest args
+This function sends the text from @var{start} to @var{end} as
standard input to a process running @var{program}. It deletes the text
-sent if @var{delete} is non-@code{nil}; this is useful when @var{buffer}
-is @code{t}, to insert the output in the current buffer.
+sent if @var{delete} is non-@code{nil}; this is useful when
+@var{destination} is @code{t}, to insert the output in the current
+buffer in place of the input.
-The arguments @var{buffer-or-name} and @var{display} control what to do
+The arguments @var{destination} and @var{display} control what to do
with the output from the subprocess, and whether to update the display
as it comes in. For details, see the description of
-@code{call-process}, above. If @var{buffer-or-name} is the integer 0,
+@code{call-process}, above. If @var{destination} is the integer 0,
@code{call-process-region} discards the output and returns @code{nil}
-immediately, without waiting for the subprocess to finish.
+immediately, without waiting for the subprocess to finish (this only
+works if asynchronous subprocesses are supported).
The remaining arguments, @var{args}, are strings that specify command
line arguments for the program.
@code{cat} utility, with standard input being the first five characters
in buffer @samp{foo} (the word @samp{input}). @code{cat} copies its
standard input into its standard output. Since the argument
-@var{buffer-or-name} is @code{t}, this output is inserted in the current
+@var{destination} is @code{t}, this output is inserted in the current
buffer.
@smallexample
@group
(call-process-region 1 6 "cat" nil t)
- @result{} nil
+ @result{} 0
---------- Buffer: foo ----------
inputinput@point{}
@smallexample
@group
-(call-process-region
- start end
+(call-process-region
+ start end
shell-file-name ; @r{Name of program.}
nil ; @r{Do not delete region.}
buffer ; @r{Send output to @code{buffer}.}
@end smallexample
@end defun
+@defun call-process-shell-command command &optional infile destination display &rest args
+This function executes the shell command @var{command} synchronously
+in a separate process. The final arguments @var{args} are additional
+arguments to add at the end of @var{command}. The other arguments
+are handled as in @code{call-process}.
+@end defun
+
+@defun shell-command-to-string command
+This function executes @var{command} (a string) as a shell command,
+then returns the command's output as a string.
+@end defun
+
@node Asynchronous Processes
@section Creating an Asynchronous Process
@cindex asynchronous subprocess
- After an @dfn{asynchronous process} is created, Emacs and the Lisp
-program both continue running immediately. The process may thereafter
-run in parallel with Emacs, and the two may communicate with each other
-using the functions described in following sections. Here we describe
-how to create an asynchronous process with @code{start-process}.
+ After an @dfn{asynchronous process} is created, Emacs and the subprocess
+both continue running immediately. The process thereafter runs
+in parallel with Emacs, and the two can communicate with each other
+using the functions described in the following sections. However,
+communication is only partially asynchronous: Emacs sends data to the
+process only when certain functions are called, and Emacs accepts data
+from the process only when Emacs is waiting for input or for a time
+delay.
+
+ Here we describe how to create an asynchronous process.
@defun start-process name buffer-or-name program &rest args
This function creates a new asynchronous subprocess and starts the
program @var{program} running in it. It returns a process object that
stands for the new subprocess in Lisp. The argument @var{name}
specifies the name for the process object; if a process with this name
-already exists, then @var{name} is modified (by adding @samp{<1>}, etc.)
-to be unique. The buffer @var{buffer-or-name} is the buffer to
+already exists, then @var{name} is modified (by appending @samp{<1>},
+etc.) to be unique. The buffer @var{buffer-or-name} is the buffer to
associate with the process.
The remaining arguments, @var{args}, are strings that specify command
This function is like @code{start-process} except that it uses a shell
to execute the specified command. The argument @var{command} is a shell
command name, and @var{command-args} are the arguments for the shell
-command.
+command. The variable @code{shell-file-name} specifies which shell to
+use.
+
+The point of running a program through the shell, rather than directly
+with @code{start-process}, is so that you can employ shell features such
+as wildcards in the arguments. It follows that if you include an
+arbitrary user-specified arguments in the command, you should quote it
+with @code{shell-quote-argument} first, so that any special shell
+characters do @emph{not} have their special shell meanings. @xref{Shell
+Arguments}.
@end defun
@defvar process-connection-type
@cindex pipes
-@cindex @sc{pty}s
+@cindex @acronym{PTY}s
This variable controls the type of device used to communicate with
-asynchronous subprocesses. If it is @code{nil}, then pipes are used.
-If it is @code{t}, then @sc{pty}s are used (or pipes if @sc{pty}s are
-not supported).
+asynchronous subprocesses. If it is non-@code{nil}, then @acronym{PTY}s are
+used, when available. Otherwise, pipes are used.
-@sc{pty}s are usually preferable for processes visible to the user, as
+@acronym{PTY}s are usually preferable for processes visible to the user, as
in Shell mode, because they allow job control (@kbd{C-c}, @kbd{C-z},
-etc.) to work between the process and its children whereas pipes do not.
-For subprocesses used for internal purposes by programs, it is often
-better to use a pipe, because they are more efficient. In addition, the
-total number of @sc{pty}s is limited on many systems and it is good not
-to waste them.
+etc.) to work between the process and its children, whereas pipes do
+not. For subprocesses used for internal purposes by programs, it is
+often better to use a pipe, because they are more efficient. In
+addition, the total number of @acronym{PTY}s is limited on many systems and
+it is good not to waste them.
-The value @code{process-connection-type} is used when
+The value of @code{process-connection-type} takes effect when
@code{start-process} is called. So you can specify how to communicate
with one subprocess by binding the variable around the call to
@code{start-process}.
(start-process @dots{}))
@end group
@end smallexample
+
+To determine whether a given subprocess actually got a pipe or a
+@acronym{PTY}, use the function @code{process-tty-name} (@pxref{Process
+Information}).
@end defvar
@node Deleting Processes
@cindex deleting processes
@dfn{Deleting a process} disconnects Emacs immediately from the
-subprocess, and removes it from the list of active processes. It sends
-a signal to the subprocess to make the subprocess terminate, but this is
-not guaranteed to happen immediately. The process object itself
-continues to exist as long as other Lisp objects point to it.
-
- You can delete a process explicitly at any time. Processes are
-deleted automatically after they terminate, but not necessarily right
-away. If you delete a terminated process explicitly before it is
-deleted automatically, no harm results.
-
-@defvar delete-exited-processes
+subprocess. Processes are deleted automatically after they terminate,
+but not necessarily right away. You can delete a process explicitly
+at any time. If you delete a terminated process explicitly before it
+is deleted automatically, no harm results. Deleting a running
+process sends a signal to terminate it (and its child processes if
+any), and calls the process sentinel if it has one. @xref{Sentinels}.
+
+ When a process is deleted, the process object itself continues to
+exist as long as other Lisp objects point to it. All the Lisp
+primitives that work on process objects accept deleted processes, but
+those that do I/O or send signals will report an error. The process
+mark continues to point to the same place as before, usually into a
+buffer where output from the process was being inserted.
+
+@defopt delete-exited-processes
This variable controls automatic deletion of processes that have
terminated (due to calling @code{exit} or to a signal). If it is
@code{nil}, then they continue to exist until the user runs
@code{list-processes}. Otherwise, they are deleted immediately after
they exit.
-@end defvar
+@end defopt
-@defun delete-process name
-This function deletes the process associated with @var{name}, killing it
-with a @code{SIGHUP} signal. The argument @var{name} may be a process,
-the name of a process, a buffer, or the name of a buffer.
+@defun delete-process process
+This function deletes a process, killing it with a @code{SIGKILL}
+signal. The argument may be a process, the name of a process, a
+buffer, or the name of a buffer. (A buffer or buffer-name stands for
+the process that @code{get-buffer-process} returns.) Calling
+@code{delete-process} on a running process terminates it, updates the
+process status, and runs the sentinel (if any) immediately. If the
+process has already terminated, calling @code{delete-process} has no
+effect on its status, or on the running of its sentinel (which will
+happen sooner or later).
@smallexample
@group
@end smallexample
@end defun
-@defun process-kill-without-query process
-This function declares that Emacs need not query the user if
-@var{process} is still running when Emacs is exited. The process will
-be deleted silently. The value is @code{t}.
-
-@smallexample
-@group
-(process-kill-without-query (get-process "shell"))
- @result{} t
-@end group
-@end smallexample
-@end defun
-
@node Process Information
@section Process Information
Several functions return information about processes.
@code{list-processes} is provided for interactive use.
-@deffn Command list-processes
+@deffn Command list-processes &optional query-only
This command displays a listing of all living processes. In addition,
it finally deletes any process whose status was @samp{Exited} or
@samp{Signaled}. It returns @code{nil}.
+
+If @var{query-only} is non-@code{nil} then it lists only processes
+whose query flag is non-@code{nil}. @xref{Query Before Exit}.
@end deffn
@defun process-list
@end defun
@defun process-id process
-This function returns the @sc{pid} of @var{process}. This is an
-integer which distinguishes the process @var{process} from all other
+This function returns the @acronym{PID} of @var{process}. This is an
+integer that distinguishes the process @var{process} from all other
processes running on the same computer at the current time. The
-@sc{pid} of a process is chosen by the operating system kernel when the
+@acronym{PID} of a process is chosen by the operating system kernel when the
process is started and remains constant as long as the process exists.
@end defun
for a network connection that is closed. Once a connection
is closed, you cannot reopen it, though you might be able to open
a new connection to the same place.
+@item connect
+for a non-blocking connection that is waiting to complete.
+@item failed
+for a non-blocking connection that has failed to complete.
+@item listen
+for a network server that is listening.
@item nil
if @var{process-name} is not the name of an existing process.
@end table
For a network connection, @code{process-status} returns one of the symbols
@code{open} or @code{closed}. The latter means that the other side
closed the connection, or Emacs did @code{delete-process}.
-
-In earlier Emacs versions (prior to version 19), the status of a network
-connection was @code{run} if open, and @code{exit} if closed.
@end defun
@defun process-exit-status process
terminated, the value is 0.
@end defun
+@defun process-tty-name process
+This function returns the terminal name that @var{process} is using for
+its communication with Emacs---or @code{nil} if it is using pipes
+instead of a terminal (see @code{process-connection-type} in
+@ref{Asynchronous Processes}).
+@end defun
+
+@defun process-coding-system process
+@anchor{Coding systems for a subprocess}
+This function returns a cons cell describing the coding systems in use
+for decoding output from @var{process} and for encoding input to
+@var{process} (@pxref{Coding Systems}). The value has this form:
+
+@example
+(@var{coding-system-for-decoding} . @var{coding-system-for-encoding})
+@end example
+@end defun
+
+@defun set-process-coding-system process &optional decoding-system encoding-system
+This function specifies the coding systems to use for subsequent output
+from and input to @var{process}. It will use @var{decoding-system} to
+decode subprocess output, and @var{encoding-system} to encode subprocess
+input.
+@end defun
+
+ Every process also has a property list that you can use to store
+miscellaneous values associated with the process.
+
+@defun process-get process propname
+This function returns the value of the @var{propname} property
+of @var{process}.
+@end defun
+
+@defun process-put process propname value
+This function sets the value of the @var{propname} property
+of @var{process} to @var{value}.
+@end defun
+
+@defun process-plist process
+This function returns the process plist of @var{process}.
+@end defun
+
+@defun set-process-plist process plist
+This function sets the process plist of @var{process} to @var{plist}.
+@end defun
+
@node Input to Processes
@section Sending Input to Processes
@cindex process input
data appears on the ``standard input'' of the subprocess.
Some operating systems have limited space for buffered input in a
-@sc{pty}. On these systems, Emacs sends an @sc{eof} periodically amidst
-the other characters, to force them through. For most programs,
-these @sc{eof}s do no harm.
-
-@defun process-send-string process-name string
-This function sends @var{process-name} the contents of @var{string} as
-standard input. The argument @var{process-name} must be a process or
-the name of a process. If it is @code{nil}, the current buffer's
-process is used.
+@acronym{PTY}. On these systems, Emacs sends an @acronym{EOF}
+periodically amidst the other characters, to force them through. For
+most programs, these @acronym{EOF}s do no harm.
+
+ Subprocess input is normally encoded using a coding system before the
+subprocess receives it, much like text written into a file. You can use
+@code{set-process-coding-system} to specify which coding system to use
+(@pxref{Process Information}). Otherwise, the coding system comes from
+@code{coding-system-for-write}, if that is non-@code{nil}; or else from
+the defaulting mechanism (@pxref{Default Coding Systems}).
+
+ Sometimes the system is unable to accept input for that process,
+because the input buffer is full. When this happens, the send functions
+wait a short while, accepting output from subprocesses, and then try
+again. This gives the subprocess a chance to read more of its pending
+input and make space in the buffer. It also allows filters, sentinels
+and timers to run---so take account of that in writing your code.
+
+ In these functions, the @var{process} argument can be a process or
+the name of a process, or a buffer or buffer name (which stands
+for a process via @code{get-buffer-process}). @code{nil} means
+the current buffer's process.
+
+@defun process-send-string process string
+This function sends @var{process} the contents of @var{string} as
+standard input. If it is @code{nil}, the current buffer's process is used.
The function returns @code{nil}.
@end smallexample
@end defun
-@deffn Command process-send-region process-name start end
+@defun process-send-region process start end
This function sends the text in the region defined by @var{start} and
-@var{end} as standard input to @var{process-name}, which is a process or
-a process name. (If it is @code{nil}, the current buffer's process is
-used.)
+@var{end} as standard input to @var{process}.
An error is signaled unless both @var{start} and @var{end} are
integers or markers that indicate positions in the current buffer. (It
is unimportant which number is larger.)
-@end deffn
-
-@defun process-send-eof &optional process-name
- This function makes @var{process-name} see an end-of-file in its
-input. The @sc{eof} comes after any text already sent to it.
+@end defun
- If @var{process-name} is not supplied, or if it is @code{nil}, then
-this function sends the @sc{eof} to the current buffer's process. An
-error is signaled if the current buffer has no process.
+@defun process-send-eof &optional process
+This function makes @var{process} see an end-of-file in its
+input. The @acronym{EOF} comes after any text already sent to it.
- The function returns @var{process-name}.
+The function returns @var{process}.
@smallexample
@group
@end smallexample
@end defun
+@defun process-running-child-p process
+@tindex process-running-child-p process
+This function will tell you whether a subprocess has given control of
+its terminal to its own child process. The value is @code{t} if this is
+true, or if Emacs cannot tell; it is @code{nil} if Emacs can be certain
+that this is not so.
+@end defun
+
@node Signals to Processes
@section Sending Signals to Processes
@cindex process signals
user hung up the phone.)
Each of the signal-sending functions takes two optional arguments:
-@var{process-name} and @var{current-group}.
+@var{process} and @var{current-group}.
- The argument @var{process-name} must be either a process, the name of
-one, or @code{nil}. If it is @code{nil}, the process defaults to the
-process associated with the current buffer. An error is signaled if
-@var{process-name} does not identify a process.
+ The argument @var{process} must be either a process, a process
+name, a buffer, a buffer name, or @code{nil}. A buffer or buffer name
+stands for a process through @code{get-buffer-process}. @code{nil}
+stands for the process associated with the current buffer. An error
+is signaled if @var{process} does not identify a process.
The argument @var{current-group} is a flag that makes a difference
when you are running a job-control shell as an Emacs subprocess. If it
is non-@code{nil}, then the signal is sent to the current process-group
-of the terminal which Emacs uses to communicate with the subprocess. If
+of the terminal that Emacs uses to communicate with the subprocess. If
the process is a job-control shell, this means the shell's current
subjob. If it is @code{nil}, the signal is sent to the process group of
the immediate subprocess of Emacs. If the subprocess is a job-control
job-control shells won't work when a pipe is used. See
@code{process-connection-type} in @ref{Asynchronous Processes}.
-@defun interrupt-process &optional process-name current-group
-This function interrupts the process @var{process-name} by sending the
+@defun interrupt-process &optional process current-group
+This function interrupts the process @var{process} by sending the
signal @code{SIGINT}. Outside of Emacs, typing the ``interrupt
character'' (normally @kbd{C-c} on some systems, and @code{DEL} on
others) sends this signal. When the argument @var{current-group} is
on the terminal by which Emacs talks to the subprocess.
@end defun
-@defun kill-process &optional process-name current-group
-This function kills the process @var{process-name} by sending the
+@defun kill-process &optional process current-group
+This function kills the process @var{process} by sending the
signal @code{SIGKILL}. This signal kills the subprocess immediately,
and cannot be handled by the subprocess.
@end defun
-@defun quit-process &optional process-name current-group
+@defun quit-process &optional process current-group
This function sends the signal @code{SIGQUIT} to the process
-@var{process-name}. This signal is the one sent by the ``quit
+@var{process}. This signal is the one sent by the ``quit
character'' (usually @kbd{C-b} or @kbd{C-\}) when you are not inside
Emacs.
@end defun
-@defun stop-process &optional process-name current-group
-This function stops the process @var{process-name} by sending the
+@defun stop-process &optional process current-group
+This function stops the process @var{process} by sending the
signal @code{SIGTSTP}. Use @code{continue-process} to resume its
execution.
-On systems with job control, the ``stop character'' (usually @kbd{C-z})
-sends this signal (outside of Emacs). When @var{current-group} is
-non-@code{nil}, you can think of this function as ``typing @kbd{C-z}''
-on the terminal Emacs uses to communicate with the subprocess.
+Outside of Emacs, on systems with job control, the ``stop character''
+(usually @kbd{C-z}) normally sends this signal. When
+@var{current-group} is non-@code{nil}, you can think of this function as
+``typing @kbd{C-z}'' on the terminal Emacs uses to communicate with the
+subprocess.
@end defun
-@defun continue-process &optional process-name current-group
+@defun continue-process &optional process current-group
This function resumes execution of the process @var{process} by sending
-it the signal @code{SIGCONT}. This presumes that @var{process-name} was
+it the signal @code{SIGCONT}. This presumes that @var{process} was
stopped previously.
@end defun
@c Emacs 19 feature
-@defun signal-process pid signal
-This function sends a signal to process @var{pid}, which need not be
-a child of Emacs. The argument @var{signal} specifies which signal
-to send; it should be an integer.
+@defun signal-process process signal
+This function sends a signal to process @var{process}. The argument
+@var{signal} specifies which signal to send; it should be an integer.
+
+The @var{process} argument can be a system process @acronym{ID}; that
+allows you to send signals to processes that are not children of
+Emacs.
@end defun
@node Output from Processes
There are two ways to receive the output that a subprocess writes to
its standard output stream. The output can be inserted in a buffer,
which is called the associated buffer of the process, or a function
-called the @dfn{filter function} can be called to act on the output.
+called the @dfn{filter function} can be called to act on the output. If
+the process has no buffer and no filter function, its output is
+discarded.
+
+ When a subprocess terminates, Emacs reads any pending output,
+then stops reading output from that subprocess. Therefore, if the
+subprocess has children that are still live and still producing
+output, Emacs won't receive that output.
+
+ Output from a subprocess can arrive only while Emacs is waiting: when
+reading terminal input, in @code{sit-for} and @code{sleep-for}
+(@pxref{Waiting}), and in @code{accept-process-output} (@pxref{Accepting
+Output}). This minimizes the problem of timing errors that usually
+plague parallel programming. For example, you can safely create a
+process and only then specify its buffer or filter function; no output
+can arrive before you finish, if the code in between does not call any
+primitive that waits.
+
+@defvar process-adaptive-read-buffering
+On some systems, when Emacs reads the output from a subprocess, the
+output data is read in very small blocks, potentially resulting in
+very poor performance. This behavior can be remedied to some extent
+by setting the variable @var{process-adaptive-read-buffering} to a
+non-@code{nil} value (the default), as it will automatically delay reading
+from such processes, thus allowing them to produce more output before
+Emacs tries to read it.
+@end defvar
+
+ It is impossible to separate the standard output and standard error
+streams of the subprocess, because Emacs normally spawns the subprocess
+inside a pseudo-TTY, and a pseudo-TTY has only one output channel. If
+you want to keep the output to those streams separate, you should
+redirect one of them to a file---for example, by using an appropriate
+shell command.
@menu
-* Process Buffers:: If no filter, output is put in a buffer.
-* Filter Functions:: Filter functions accept output from the process.
-* Accepting Output:: Explicitly permitting subprocess output.
- Waiting for subprocess output.
+* Process Buffers:: If no filter, output is put in a buffer.
+* Filter Functions:: Filter functions accept output from the process.
+* Decoding Output:: Filters can get unibyte or multibyte strings.
+* Accepting Output:: How to wait until process output arrives.
@end menu
@node Process Buffers
Unless the process has a filter function (@pxref{Filter Functions}),
its output is inserted in the associated buffer. The position to insert
-the output is determined by the @code{process-mark} (@pxref{Process
-Information}), which is then updated to point to the end of the text
-just inserted. Usually, but not always, the @code{process-mark} is at
-the end of the buffer. If the process has no buffer and no filter
-function, its output is discarded.
+the output is determined by the @code{process-mark}, which is then
+updated to point to the end of the text just inserted. Usually, but not
+always, the @code{process-mark} is at the end of the buffer.
@defun process-buffer process
This function returns the associated buffer of the process
the end of the following section.
When the user is expected to enter input in the process buffer for
-transmission to the process, the process marker is useful for
-distinguishing the new input from previous output.
+transmission to the process, the process marker separates the new input
+from previous output.
@end defun
@defun set-process-buffer process buffer
@end defun
@defun get-buffer-process buffer-or-name
-This function returns the process associated with @var{buffer-or-name}.
-If there are several processes associated with it, then one is chosen.
-(Presently, the one chosen is the one most recently created.) It is
-usually a bad idea to have more than one process associated with the
-same buffer.
+This function returns a nondeleted process associated with the buffer
+specified by @var{buffer-or-name}. If there are several processes
+associated with it, this function chooses one (currently, the one most
+recently created, but don't count on that). Deletion of a process
+(see @code{delete-process}) makes it ineligible for this function to
+return.
+
+It is usually a bad idea to have more than one process associated with
+the same buffer.
@smallexample
@group
A process @dfn{filter function} is a function that receives the
standard output from the associated process. If a process has a filter,
-then @emph{all} output from that process, that would otherwise have been
-in a buffer, is passed to the filter. The process buffer is used
-directly for output from the process only when there is no filter.
+then @emph{all} output from that process is passed to the filter. The
+process buffer is used directly for output from the process only when
+there is no filter.
- A filter function must accept two arguments: the associated process and
-a string, which is the output. The function is then free to do whatever it
-chooses with the output.
+ The filter function can only be called when Emacs is waiting for
+something, because process output arrives only at such times. Emacs
+waits when reading terminal input, in @code{sit-for} and
+@code{sleep-for} (@pxref{Waiting}), and in @code{accept-process-output}
+(@pxref{Accepting Output}).
- A filter function runs only while Emacs is waiting (e.g., for terminal
-input, or for time to elapse, or for process output). This avoids the
-timing errors that could result from running filters at random places in
-the middle of other Lisp programs. You may explicitly cause Emacs to
-wait, so that filter functions will run, by calling @code{sit-for},
-@code{sleep-for} or @code{accept-process-output} (@pxref{Accepting
-Output}). Emacs is also waiting when the command loop is reading input.
+ A filter function must accept two arguments: the associated process
+and a string, which is output just received from it. The function is
+then free to do whatever it chooses with the output.
Quitting is normally inhibited within a filter function---otherwise,
the effect of typing @kbd{C-g} at command level or to quit a user
-command would be unpredictable. If you want to permit quitting inside a
-filter function, bind @code{inhibit-quit} to @code{nil}.
-@xref{Quitting}.
+command would be unpredictable. If you want to permit quitting inside
+a filter function, bind @code{inhibit-quit} to @code{nil}. In most
+cases, the right way to do this is with the macro
+@code{with-local-quit}. @xref{Quitting}.
+
+ If an error happens during execution of a filter function, it is
+caught automatically, so that it doesn't stop the execution of whatever
+program was running when the filter function was started. However, if
+@code{debug-on-error} is non-@code{nil}, the error-catching is turned
+off. This makes it possible to use the Lisp debugger to debug the
+filter function. @xref{Debugger}.
Many filter functions sometimes or always insert the text in the
process's buffer, mimicking the actions of Emacs when there is no
filter. Such filter functions need to use @code{set-buffer} in order to
be sure to insert in that buffer. To avoid setting the current buffer
-semipermanently, these filter functions must use @code{unwind-protect}
-to make sure to restore the previous current buffer. They should also
-update the process marker, and in some cases update the value of point.
-Here is how to do these things:
+semipermanently, these filter functions must save and restore the
+current buffer. They should also update the process marker, and in some
+cases update the value of point. Here is how to do these things:
@smallexample
@group
(defun ordinary-insertion-filter (proc string)
- (let ((old-buffer (current-buffer)))
- (unwind-protect
- (let (moving)
- (set-buffer (process-buffer proc))
- (setq moving (= (point) (process-mark proc)))
+ (with-current-buffer (process-buffer proc)
+ (let ((moving (= (point) (process-mark proc))))
@end group
@group
- (save-excursion
- ;; @r{Insert the text, moving the process-marker.}
- (goto-char (process-mark proc))
- (insert string)
- (set-marker (process-mark proc) (point)))
- (if moving (goto-char (process-mark proc))))
- (set-buffer old-buffer))))
+ (save-excursion
+ ;; @r{Insert the text, advancing the process marker.}
+ (goto-char (process-mark proc))
+ (insert string)
+ (set-marker (process-mark proc) (point)))
+ (if moving (goto-char (process-mark proc))))))
@end group
@end smallexample
@noindent
-The reason to use an explicit @code{unwind-protect} rather than letting
-@code{save-excursion} restore the current buffer is so as to preserve
-the change in point made by @code{goto-char}.
+The reason to use @code{with-current-buffer}, rather than using
+@code{save-excursion} to save and restore the current buffer, is so as
+to preserve the change in point made by the second call to
+@code{goto-char}.
To make the filter force the process buffer to be visible whenever new
text arrives, insert the following line just before the
-@code{unwind-protect}:
+@code{with-current-buffer} construct:
@smallexample
(display-buffer (process-buffer proc))
@end smallexample
- To force point to move to the end of the new output no matter where
-it was previously, eliminate the variable @code{moving} and call
+ To force point to the end of the new output, no matter where it was
+previously, eliminate the variable @code{moving} and call
@code{goto-char} unconditionally.
- All filter functions that do regexp searching or matching should save
-and restore the match data. Otherwise, a filter function that runs
-during a call to @code{sit-for} might clobber the match data of the
-program that called @code{sit-for}. @xref{Match Data}.
+ In earlier Emacs versions, every filter function that did regular
+expression searching or matching had to explicitly save and restore the
+match data. Now Emacs does this automatically for filter functions;
+they never need to do it explicitly. @xref{Match Data}.
A filter function that writes the output into the buffer of the
-process should check whether the process is still alive. If it tries to
-insert into a dead buffer, it will get an error. If the buffer is dead,
-@code{(buffer-name (process-buffer @var{process}))} returns @code{nil}.
+process should check whether the buffer is still alive. If it tries to
+insert into a dead buffer, it will get an error. The expression
+@code{(buffer-name (process-buffer @var{process}))} returns @code{nil}
+if the buffer is dead.
The output to the function may come in chunks of any size. A program
-that produces the same output twice in a row may send it as one batch
-of 200 characters one time, and five batches of 40 characters the next.
+that produces the same output twice in a row may send it as one batch of
+200 characters one time, and five batches of 40 characters the next. If
+the filter looks for certain text strings in the subprocess output, make
+sure to handle the case where one of these strings is split across two
+or more batches of output.
@defun set-process-filter process filter
This function gives @var{process} the filter function @var{filter}. If
;; @r{Insert input in the buffer specified by @code{my-shell-buffer}}
;; @r{and make sure that buffer is shown in some window.}
(defun my-process-filter (proc str)
- (let ((cur (selected-window))
- (pop-up-windows t))
- (pop-to-buffer my-shell-buffer)
+ (let ((cur (selected-window))
+ (pop-up-windows t))
+ (pop-to-buffer my-shell-buffer)
@end group
@group
- (goto-char (point-max))
- (insert str)
- (set-marker (process-mark proc) (point-max))
- (select-window cur)))
+ (goto-char (point-max))
+ (insert str)
+ (set-marker (process-mark proc) (point-max))
+ (select-window cur)))
@end group
@end smallexample
@end ignore
+@node Decoding Output
+@subsection Decoding Process Output
+
+ When Emacs writes process output directly into a multibyte buffer,
+it decodes the output according to the process output coding system.
+If the coding system is @code{raw-text} or @code{no-conversion}, Emacs
+converts the unibyte output to multibyte using
+@code{string-to-multibyte}, and inserts the resulting multibyte text.
+
+ You can use @code{set-process-coding-system} to specify which coding
+system to use (@pxref{Process Information}). Otherwise, the coding
+system comes from @code{coding-system-for-read}, if that is
+non-@code{nil}; or else from the defaulting mechanism (@pxref{Default
+Coding Systems}).
+
+ @strong{Warning:} Coding systems such as @code{undecided} which
+determine the coding system from the data do not work entirely
+reliably with asynchronous subprocess output. This is because Emacs
+has to process asynchronous subprocess output in batches, as it
+arrives. Emacs must try to detect the proper coding system from one
+batch at a time, and this does not always work. Therefore, if at all
+possible, specify a coding system that determines both the character
+code conversion and the end of line conversion---that is, one like
+@code{latin-1-unix}, rather than @code{undecided} or @code{latin-1}.
+
+@cindex filter multibyte flag, of process
+@cindex process filter multibyte flag
+ When Emacs calls a process filter function, it provides the process
+output as a multibyte string or as a unibyte string according to the
+process's filter multibyte flag. If the flag is non-@code{nil}, Emacs
+decodes the output according to the process output coding system to
+produce a multibyte string, and passes that to the process. If the
+flag is @code{nil}, Emacs puts the output into a unibyte string, with
+no decoding, and passes that.
+
+ When you create a process, the filter multibyte flag takes its
+initial value from @code{default-enable-multibyte-characters}. If you
+want to change the flag later on, use
+@code{set-process-filter-multibyte}.
+
+@defun set-process-filter-multibyte process multibyte
+This function sets the filter multibyte flag of @var{process}
+to @var{multibyte}.
+@end defun
+
+@defun process-filter-multibyte-p process
+This function returns the filter multibyte flag of @var{process}.
+@end defun
+
@node Accepting Output
@subsection Accepting Output from Processes
explicitly permit output to arrive at a specific point, or even to wait
until output arrives from a process.
-@defun accept-process-output &optional process seconds millisec
+@defun accept-process-output &optional process seconds millisec just-this-one
This function allows Emacs to read pending output from processes. The
output is inserted in the associated buffers or given to their filter
functions. If @var{process} is non-@code{nil} then this function does
returns after that much time whether or not there has been any
subprocess output.
-Not all operating systems support waiting periods other than multiples
-of a second; on those that do not, you get an error if you specify
-nonzero @var{millisec}.
+The argument @var{seconds} need not be an integer. If it is a floating
+point number, this function waits for a fractional number of seconds.
+
+@c Emacs 22.1 feature
+If @var{process} is a process, and the argument @var{just-this-one} is
+non-@code{nil}, only output from that process is handled, suspending output
+from other processes until some output has been received from that
+process or the timeout expires. If @var{just-this-one} is an integer,
+also inhibit running timers. This feature is generally not
+recommended, but may be necessary for specific applications, such as
+speech synthesis.
The function @code{accept-process-output} returns non-@code{nil} if it
did get some output, or @code{nil} if the timeout expired before output
A @dfn{process sentinel} is a function that is called whenever the
associated process changes status for any reason, including signals
(whether sent by Emacs or caused by the process's own actions) that
-terminate, stop, or continue the process. The process sentinel is also
-called if the process exits. The sentinel receives two arguments: the
-process for which the event occurred, and a string describing the type
-of event.
+terminate, stop, or continue the process. The process sentinel is
+also called if the process exits. The sentinel receives two
+arguments: the process for which the event occurred, and a string
+describing the type of event.
The string describing the event looks like one of the following:
@itemize @bullet
-@item
+@item
@code{"finished\n"}.
@item
@code{"@var{name-of-signal} (core dumped)\n"}.
@end itemize
- A sentinel runs only while Emacs is waiting (e.g., for terminal input,
-or for time to elapse, or for process output). This avoids the timing
-errors that could result from running them at random places in the
-middle of other Lisp programs. A program can wait, so that sentinels
-will run, by calling @code{sit-for}, @code{sleep-for} or
-@code{accept-process-output} (@pxref{Accepting Output}). Emacs is also
-waiting when the command loop is reading input.
+ A sentinel runs only while Emacs is waiting (e.g., for terminal
+input, or for time to elapse, or for process output). This avoids the
+timing errors that could result from running them at random places in
+the middle of other Lisp programs. A program can wait, so that
+sentinels will run, by calling @code{sit-for} or @code{sleep-for}
+(@pxref{Waiting}), or @code{accept-process-output} (@pxref{Accepting
+Output}). Emacs also allows sentinels to run when the command loop is
+reading input. @code{delete-process} calls the sentinel when it
+terminates a running process.
+
+ Emacs does not keep a queue of multiple reasons to call the sentinel
+of one process; it records just the current status and the fact that
+there has been a change. Therefore two changes in status, coming in
+quick succession, can call the sentinel just once. However, process
+termination will always run the sentinel exactly once. This is
+because the process status can't change again after termination.
+
+ Emacs explicitly checks for output from the process before running
+the process sentinel. Once the sentinel runs due to process
+termination, no further output can arrive from the process.
+
+ A sentinel that writes the output into the buffer of the process
+should check whether the buffer is still alive. If it tries to insert
+into a dead buffer, it will get an error. If the buffer is dead,
+@code{(buffer-name (process-buffer @var{process}))} returns @code{nil}.
Quitting is normally inhibited within a sentinel---otherwise, the
effect of typing @kbd{C-g} at command level or to quit a user command
would be unpredictable. If you want to permit quitting inside a
-sentinel, bind @code{inhibit-quit} to @code{nil}. @xref{Quitting}.
+sentinel, bind @code{inhibit-quit} to @code{nil}. In most cases, the
+right way to do this is with the macro @code{with-local-quit}.
+@xref{Quitting}.
- A sentinel that writes the output into the buffer of the process
-should check whether the process is still alive. If it tries to insert
-into a dead buffer, it will get an error. If the buffer is dead,
-@code{(buffer-name (process-buffer @var{process}))} returns @code{nil}.
+ If an error happens during execution of a sentinel, it is caught
+automatically, so that it doesn't stop the execution of whatever
+programs was running when the sentinel was started. However, if
+@code{debug-on-error} is non-@code{nil}, the error-catching is turned
+off. This makes it possible to use the Lisp debugger to debug the
+sentinel. @xref{Debugger}.
- All sentinels that do regexp searching or matching should save and
-restore the match data. Otherwise, a sentinel that runs during a call
-to @code{sit-for} might clobber the match data of the program that
-called @code{sit-for}. @xref{Match Data}.
+ While a sentinel is running, the process sentinel is temporarily
+set to @code{nil} so that the sentinel won't run recursively.
+For this reason it is not possible for a sentinel to specify
+a new sentinel.
+
+ In earlier Emacs versions, every sentinel that did regular expression
+searching or matching had to explicitly save and restore the match data.
+Now Emacs does this automatically for sentinels; they never need to do
+it explicitly. @xref{Match Data}.
@defun set-process-sentinel process sentinel
This function associates @var{sentinel} with @var{process}. If
The default behavior when there is no sentinel is to insert a message in
the process's buffer when the process status changes.
+Changes in process sentinel take effect immediately---if the sentinel
+is slated to be run but has not been called yet, and you specify a new
+sentinel, the eventual call to the sentinel will use the new one.
+
@smallexample
@group
(defun msg-me (process event)
was not.
@end defun
+@node Query Before Exit
+@section Querying Before Exit
+
+ When Emacs exits, it terminates all its subprocesses by sending them
+the @code{SIGHUP} signal. Because subprocesses may be doing
+valuable work, Emacs normally asks the user to confirm that it is ok
+to terminate them. Each process has a query flag which, if
+non-@code{nil}, says that Emacs should ask for confirmation before
+exiting and thus killing that process. The default for the query flag
+is @code{t}, meaning @emph{do} query.
+
+@tindex process-query-on-exit-flag
+@defun process-query-on-exit-flag process
+This returns the query flag of @var{process}.
+@end defun
+
+@tindex set-process-query-on-exit-flag
+@defun set-process-query-on-exit-flag process flag
+This function sets the query flag of @var{process} to @var{flag}. It
+returns @var{flag}.
+
+@smallexample
+@group
+;; @r{Don't query about the shell process}
+(set-process-query-on-exit-flag (get-process "shell") nil)
+ @result{} t
+@end group
+@end smallexample
+@end defun
+
+@defun process-kill-without-query process &optional do-query
+This function clears the query flag of @var{process}, so that
+Emacs will not query the user on account of that process.
+
+Actually, the function does more than that: it returns the old value of
+the process's query flag, and sets the query flag to @var{do-query}.
+Please don't use this function to do those things any more---please
+use the newer, cleaner functions @code{process-query-on-exit-flag} and
+@code{set-process-query-on-exit-flag} in all but the simplest cases.
+The only way you should use @code{process-kill-without-query} nowadays
+is like this:
+
+@smallexample
+@group
+;; @r{Don't query about the shell process}
+(process-kill-without-query (get-process "shell"))
+@end group
+@end smallexample
+@end defun
+
@node Transaction Queues
@section Transaction Queues
@cindex transaction queue
-You can use a @dfn{transaction queue} for more convenient communication
-with subprocesses using transactions. First use @code{tq-create} to
-create a transaction queue communicating with a specified process. Then
-you can call @code{tq-enqueue} to send a transaction.
+You can use a @dfn{transaction queue} to communicate with a subprocess
+using transactions. First use @code{tq-create} to create a transaction
+queue communicating with a specified process. Then you can call
+@code{tq-enqueue} to send a transaction.
@defun tq-create process
This function creates and returns a transaction queue communicating with
@var{process}. The argument @var{process} should be a subprocess
capable of sending and receiving streams of bytes. It may be a child
-process, or it may be a TCP connection to a server possibly on another
+process, or it may be a TCP connection to a server, possibly on another
machine.
@end defun
-@defun tq-enqueue queue question regexp closure fn
+@defun tq-enqueue queue question regexp closure fn &optional delay-question
This function sends a transaction to queue @var{queue}. Specifying the
queue has the effect of specifying the subprocess to talk to.
-The argument @var{question} is the outgoing message which starts the
+The argument @var{question} is the outgoing message that starts the
transaction. The argument @var{fn} is the function to call when the
corresponding answer comes back; it is called with two arguments:
@var{closure}, and the answer received.
-The argument @var{regexp} is a regular expression that should match the
-entire answer, but nothing less; that's how @code{tq-enqueue} determines
-where the answer ends.
+The argument @var{regexp} is a regular expression that should match
+text at the end of the entire answer, but nothing before; that's how
+@code{tq-enqueue} determines where the answer ends.
+
+If the argument @var{delay-question} is non-nil, delay sending this
+question until the process has finished replying to any previous
+questions. This produces more reliable results with some processes."
The return value of @code{tq-enqueue} itself is not meaningful.
@end defun
Transaction queues are implemented by means of a filter function.
@xref{Filter Functions}.
-@node TCP
-@section TCP
+@node Network
+@section Network Connections
+@cindex network connection
@cindex TCP
-
- Emacs Lisp programs can open TCP connections to other processes on the
-same machine or other machines. A network connection is handled by Lisp
-much like a subprocess, and is represented by a process object.
-However, the process you are communicating with is not a child of the
-Emacs process, so you can't kill it or send it signals. All you can do
-is send and receive data. @code{delete-process} closes the connection,
-but does not kill the process at the other end; that process must decide
-what to do about closure of the connection.
+@cindex UDP
+
+ Emacs Lisp programs can open stream (TCP) and datagram (UDP) network
+connections to other processes on the same machine or other machines.
+A network connection is handled by Lisp much like a subprocess, and is
+represented by a process object. However, the process you are
+communicating with is not a child of the Emacs process, so it has no
+process @acronym{ID}, and you can't kill it or send it signals. All you
+can do is send and receive data. @code{delete-process} closes the
+connection, but does not kill the program at the other end; that
+program must decide what to do about closure of the connection.
+
+ Lisp programs can listen for connections by creating network
+servers. A network server is also represented by a kind of process
+object, but unlike a network connection, the network server never
+transfers data itself. When it receives a connection request, it
+creates a new network connection to represent the connection just
+made. (The network connection inherits certain information, including
+the process plist, from the server.) The network server then goes
+back to listening for more connection requests.
+
+ Network connections and servers are created by calling
+@code{make-network-process} with an argument list consisting of
+keyword/argument pairs, for example @code{:server t} to create a
+server process, or @code{:type 'datagram} to create a datagram
+connection. @xref{Low-Level Network}, for details. You can also use
+the @code{open-network-stream} function described below.
You can distinguish process objects representing network connections
-from those representing subprocesses with the @code{process-status}
-function. @xref{Process Information}.
+and servers from those representing subprocesses with the
+@code{process-status} function. The possible status values for
+network connections are @code{open}, @code{closed}, @code{connect},
+and @code{failed}. For a network server, the status is always
+@code{listen}. None of those values is possible for a real
+subprocess. @xref{Process Information}.
+
+ You can stop and resume operation of a network process by calling
+@code{stop-process} and @code{continue-process}. For a server
+process, being stopped means not accepting new connections. (Up to 5
+connection requests will be queued for when you resume the server; you
+can increase this limit, unless it is imposed by the operating
+system.) For a network stream connection, being stopped means not
+processing input (any arriving input waits until you resume the
+connection). For a datagram connection, some number of packets may be
+queued but input may be lost. You can use the function
+@code{process-command} to determine whether a network connection or
+server is stopped; a non-@code{nil} value means yes.
@defun open-network-stream name buffer-or-name host service
-This function opens a TCP connection for a service to a host. It
-returns a process object to represent the connection.
+This function opens a TCP connection, and returns a process object
+that represents the connection.
The @var{name} argument specifies the name for the process object. It
is modified as necessary to make it unique.
@var{host} is the host name (a string), and @var{service} is the name of
a defined network service (a string) or a port number (an integer).
@end defun
+
+@defun process-contact process &optional key
+This function returns information about how a network process was set
+up. For a connection, when @var{key} is @code{nil}, it returns
+@code{(@var{hostname} @var{service})} which specifies what you
+connected to.
+
+If @var{key} is @code{t}, the value is the complete status information
+for the connection or server; that is, the list of keywords and values
+specified in @code{make-network-process}, except that some of the
+values represent the current status instead of what you specified:
+
+@table @code
+@item :buffer
+The associated value is the process buffer.
+@item :filter
+The associated value is the process filter function.
+@item :sentinel
+The associated value is the process sentinel function.
+@item :remote
+In a connection, this is the address in internal format of the remote peer.
+@item :local
+The local address, in internal format.
+@item :service
+In a server, if you specified @code{t} for @var{service},
+this value is the actual port number.
+@end table
+
+@code{:local} and @code{:remote} are included even if they were not
+specified explicitly in @code{make-network-process}.
+
+If @var{key} is a keyword, the function returns the value corresponding
+to that keyword.
+
+For an ordinary child process, this function always returns @code{t}.
+@end defun
+
+@node Network Servers
+@section Network Servers
+
+ You create a server by calling @code{make-network-process} with
+@code{:server t}. The server will listen for connection requests from
+clients. When it accepts a client connection request, that creates a
+new network connection, itself a process object, with the following
+parameters:
+
+@itemize @bullet
+@item
+The connection's process name is constructed by concatenating the
+server process' @var{name} with a client identification string. The
+client identification string for an IPv4 connection looks like
+@samp{<@var{a}.@var{b}.@var{c}.@var{d}:@var{p}>}. Otherwise, it is a
+unique number in brackets, as in @samp{<@var{nnn}>}. The number
+is unique for each connection in the Emacs session.
+
+@item
+If the server's filter is non-@code{nil}, the connection process does
+not get a separate process buffer; otherwise, Emacs creates a new
+buffer for the purpose. The buffer name is the server's buffer name
+or process name, concatenated with the client identification string.
+
+The server's process buffer value is never used directly by Emacs, but
+it is passed to the log function, which can log connections by
+inserting text there.
+
+@item
+The communication type and the process filter and sentinel are
+inherited from those of the server. The server never directly
+uses its filter and sentinel; their sole purpose is to initialize
+connections made to the server.
+
+@item
+The connection's process contact info is set according to the client's
+addressing information (typically an IP address and a port number).
+This information is associated with the @code{process-contact}
+keywords @code{:host}, @code{:service}, @code{:remote}.
+
+@item
+The connection's local address is set up according to the port
+number used for the connection.
+
+@item
+The client process' plist is initialized from the server's plist.
+@end itemize
+
+@node Datagrams
+@section Datagrams
+@cindex datagrams
+
+ A datagram connection communicates with individual packets rather
+than streams of data. Each call to @code{process-send} sends one
+datagram packet (@pxref{Input to Processes}), and each datagram
+received results in one call to the filter function.
+
+ The datagram connection doesn't have to talk with the same remote
+peer all the time. It has a @dfn{remote peer address} which specifies
+where to send datagrams to. Each time an incoming datagram is passed
+to the filter function, the peer address is set to the address that
+datagram came from; that way, if the filter function sends a datagram,
+it will go back to that place. You can specify the remote peer
+address when you create the datagram connection using the
+@code{:remote} keyword. You can change it later on by calling
+@code{set-process-datagram-address}.
+
+@defun process-datagram-address process
+If @var{process} is a datagram connection or server, this function
+returns its remote peer address.
+@end defun
+
+@defun set-process-datagram-address process address
+If @var{process} is a datagram connection or server, this function
+sets its remote peer address to @var{address}.
+@end defun
+
+@node Low-Level Network
+@section Low-Level Network Access
+
+ You can also create network connections by operating at a lower
+level that that of @code{open-network-stream}, using
+@code{make-network-process}.
+
+@menu
+* Make Network:: Using @code{make-network-process}.
+* Network Options:: Further control over network connections.
+* Network Feature Testing:: Determining which network features work on
+ the machine you are using.
+@end menu
+
+@node Make Network
+@subsection @code{make-network-process}
+
+ The basic function for creating network connections and network
+servers is @code{make-network-process}. It can do either of those
+jobs, depending on the arguments you give it.
+
+@defun make-network-process &rest args
+This function creates a network connection or server and returns the
+process object that represents it. The arguments @var{args} are a
+list of keyword/argument pairs. Omitting a keyword is always
+equivalent to specifying it with value @code{nil}, except for
+@code{:coding}, @code{:filter-multibyte}, and @code{:reuseaddr}. Here
+are the meaningful keywords:
+
+@table @asis
+@item :name @var{name}
+Use the string @var{name} as the process name. It is modified if
+necessary to make it unique.
+
+@item :type @var{type}
+Specify the communication type. A value of @code{nil} specifies a
+stream connection (the default); @code{datagram} specifies a datagram
+connection. Both connections and servers can be of either type.
+
+@item :server @var{server-flag}
+If @var{server-flag} is non-@code{nil}, create a server. Otherwise,
+create a connection. For a stream type server, @var{server-flag} may
+be an integer which then specifies the length of the queue of pending
+connections to the server. The default queue length is 5.
+
+@item :host @var{host}
+Specify the host to connect to. @var{host} should be a host name or
+internet address, as a string, or the symbol @code{local} to specify
+the local host. If you specify @var{host} for a server, it must
+specify a valid address for the local host, and only clients
+connecting to that address will be accepted.
+
+@item :service @var{service}
+@var{service} specifies a port number to connect to, or, for a server,
+the port number to listen on. It should be a service name that
+translates to a port number, or an integer specifying the port number
+directly. For a server, it can also be @code{t}, which means to let
+the system select an unused port number.
+
+@item :family @var{family}
+@var{family} specifies the address (and protocol) family for
+communication. @code{nil} means determine the proper address family
+automatically for the given @var{host} and @var{service}.
+@code{local} specifies a Unix socket, in which case @var{host} is
+ignored. @code{ipv4} and @code{ipv6} specify to use IPv4 and IPv6
+respectively.
+
+@item :local @var{local-address}
+For a server process, @var{local-address} is the address to listen on.
+It overrides @var{family}, @var{host} and @var{service}, and you
+may as well not specify them.
+
+@item :remote @var{remote-address}
+For a connection, @var{remote-address} is the address to connect to.
+It overrides @var{family}, @var{host} and @var{service}, and you
+may as well not specify them.
+
+For a datagram server, @var{remote-address} specifies the initial
+setting of the remote datagram address.
+
+The format of @var{local-address} or @var{remote-address} depends on
+the address family:
+
+@itemize -
+@item
+An IPv4 address is represented as a five-element vector of four 8-bit
+integers and one 16-bit integer
+@code{[@var{a} @var{b} @var{c} @var{d} @var{p}]} corresponding to
+numeric IPv4 address @var{a}.@var{b}.@var{c}.@var{d} and port number
+@var{p}.
+
+@item
+An IPv6 address is represented as a nine-element vector of 16-bit
+integers @code{[@var{a} @var{b} @var{c} @var{d} @var{e} @var{f}
+@var{g} @var{h} @var{p}]} corresponding to numeric IPv6 address
+@var{a}:@var{b}:@var{c}:@var{d}:@var{e}:@var{f}:@var{g}:@var{h} and
+port number @var{p}.
+
+@item
+A local address is represented as a string which specifies the address
+in the local address space.
+
+@item
+An ``unsupported family'' address is represented by a cons
+@code{(@var{f} . @var{av})}, where @var{f} is the family number and
+@var{av} is a vector specifying the socket address using one element
+per address data byte. Do not rely on this format in portable code,
+as it may depend on implementation defined constants, data sizes, and
+data structure alignment.
+@end itemize
+
+@item :nowait @var{bool}
+If @var{bool} is non-@code{nil} for a stream connection, return
+without waiting for the connection to complete. When the connection
+succeeds or fails, Emacs will call the sentinel function, with a
+second argument matching @code{"open"} (if successful) or
+@code{"failed"}. The default is to block, so that
+@code{make-network-process} does not return until the connection
+has succeeded or failed.
+
+@item :stop @var{stopped}
+Start the network connection or server in the `stopped' state if
+@var{stopped} is non-@code{nil}.
+
+@item :buffer @var{buffer}
+Use @var{buffer} as the process buffer.
+
+@item :coding @var{coding}
+Use @var{coding} as the coding system for this process. To specify
+different coding systems for decoding data from the connection and for
+encoding data sent to it, specify @code{(@var{decoding} .
+@var{encoding})} for @var{coding}.
+
+If you don't specify this keyword at all, the default
+is to determine the coding systems from the data.
+
+@item :noquery @var{query-flag}
+Initialize the process query flag to @var{query-flag}.
+@xref{Query Before Exit}.
+
+@item :filter @var{filter}
+Initialize the process filter to @var{filter}.
+
+@item :filter-multibyte @var{bool}
+If @var{bool} is non-@code{nil}, strings given to the process filter
+are multibyte, otherwise they are unibyte. If you don't specify this
+keyword at all, the default is that the strings are multibyte if
+@code{default-enable-multibyte-characters} is non-@code{nil}.
+
+@item :sentinel @var{sentinel}
+Initialize the process sentinel to @var{sentinel}.
+
+@item :log @var{log}
+Initialize the log function of a server process to @var{log}. The log
+function is called each time the server accepts a network connection
+from a client. The arguments passed to the log function are
+@var{server}, @var{connection}, and @var{message}, where @var{server}
+is the server process, @var{connection} is the new process for the
+connection, and @var{message} is a string describing what has
+happened.
+
+@item :plist @var{plist}
+Initialize the process plist to @var{plist}.
+@end table
+
+The original argument list, modified with the actual connection
+information, is available via the @code{process-contact} function.
+@end defun
+
+@node Network Options
+@subsection Network Options
+
+ The following network options can be specified when you create a
+network process. Except for @code{:reuseaddr}, you can also set or
+modify these options later, using @code{set-network-process-option}.
+
+ For a server process, the options specified with
+@code{make-network-process} are not inherited by the client
+connections, so you will need to set the necessary options for each
+child connection as it is created.
+
+@table @asis
+@item :bindtodevice @var{device-name}
+If @var{device-name} is a non-empty string identifying a network
+interface name (see @code{network-interface-list}), only handle
+packets received on that interface. If @var{device-name} is @code{nil}
+(the default), handle packets received on any interface.
+
+Using this option may require special privileges on some systems.
+
+@item :broadcast @var{broadcast-flag}
+If @var{broadcast-flag} is non-@code{nil} for a datagram process, the
+process will receive datagram packet sent to a broadcast address, and
+be able to send packets to a broadcast address. Ignored for a stream
+connection.
+
+@item :dontroute @var{dontroute-flag}
+If @var{dontroute-flag} is non-@code{nil}, the process can only send
+to hosts on the same network as the local host.
+
+@item :keepalive @var{keepalive-flag}
+If @var{keepalive-flag} is non-@code{nil} for a stream connection,
+enable exchange of low-level keep-alive messages.
+
+@item :linger @var{linger-arg}
+If @var{linger-arg} is non-@code{nil}, wait for successful
+transmission of all queued packets on the connection before it is
+deleted (see @code{delete-process}). If @var{linger-arg} is an
+integer, it specifies the maximum time in seconds to wait for queued
+packets to be sent before closing the connection. Default is
+@code{nil} which means to discard unsent queued packets when the
+process is deleted.
+
+@item :oobinline @var{oobinline-flag}
+If @var{oobinline-flag} is non-@code{nil} for a stream connection,
+receive out-of-band data in the normal data stream. Otherwise, ignore
+out-of-band data.
+
+@item :priority @var{priority}
+Set the priority for packets sent on this connection to the integer
+@var{priority}. The interpretation of this number is protocol
+specific, such as setting the TOS (type of service) field on IP
+packets sent on this connection. It may also have system dependent
+effects, such as selecting a specific output queue on the network
+interface.
+
+@item :reuseaddr @var{reuseaddr-flag}
+If @var{reuseaddr-flag} is non-@code{nil} (the default) for a stream
+server process, allow this server to reuse a specific port number (see
+@code{:service}) unless another process on this host is already
+listening on that port. If @var{reuseaddr-flag} is @code{nil}, there
+may be a period of time after the last use of that port (by any
+process on the host), where it is not possible to make a new server on
+that port.
+@end table
+
+@defun set-network-process-option process option value
+This function sets or modifies a network option for network process
+@var{process}. See @code{make-network-process} for details of options
+@var{option} and their corresponding values @var{value}.
+
+The current setting of an option is available via the
+@code{process-contact} function.
+@end defun
+
+@node Network Feature Testing
+@subsection Testing Availability of Network Features
+
+ To test for the availability of a given network feature, use
+@code{featurep} like this:
+
+@example
+(featurep 'make-network-process '(@var{keyword} @var{value}))
+@end example
+
+@noindent
+The result of the first form is @code{t} if it works to specify
+@var{keyword} with value @var{value} in @code{make-network-process}.
+The result of the second form is @code{t} if @var{keyword} is
+supported by @code{make-network-process}. Here are some of the
+@var{keyword}---@var{value} pairs you can test in
+this way.
+
+@table @code
+@item (:nowait t)
+Non-@code{nil} if non-blocking connect is supported.
+@item (:type datagram)
+Non-@code{nil} if datagrams are supported.
+@item (:family local)
+Non-@code{nil} if local (aka ``UNIX domain'') sockets are supported.
+@item (:family ipv6)
+Non-@code{nil} if IPv6 is supported.
+@item (:service t)
+Non-@code{nil} if the system can select the port for a server.
+@end table
+
+ To test for the availability of a given network option, use
+@code{featurep} like this:
+
+@example
+(featurep 'make-network-process '@var{keyword})
+@end example
+
+@noindent
+Here are some of the options you can test in this way.
+
+@table @code
+@item :bindtodevice
+@itemx :broadcast
+@itemx :dontroute
+@itemx :keepalive
+@itemx :linger
+@itemx :oobinline
+@itemx :priority
+@itemx :reuseaddr
+That particular network option is supported by
+@code{make-network-process} and @code{set-network-process-option}.
+@end table
+
+@node Misc Network
+@section Misc Network Facilities
+
+ These additional functions are useful for creating and operating
+on network connections.
+
+@defun network-interface-list
+This function returns a list describing the network interfaces
+of the machine you are using. The value is an alist whose
+elements have the form @code{(@var{name} . @var{address})}.
+@var{address} has the same form as the @var{local-address}
+and @var{remote-address} arguments to @code{make-network-process}.
+@end defun
+
+@defun network-interface-info ifname
+This function returns information about the network interface named
+@var{ifname}. The value is a list of the form
+@code{(@var{addr} @var{bcast} @var{netmask} @var{hwaddr} @var{flags})}.
+
+@table @var
+@item addr
+The internet protocol address.
+@item bcast
+The broadcast address.
+@item netmask
+The network mask.
+@item hwaddr
+The layer 2 address (Ethernet MAC address, for instance).
+@item flags
+The current flags of the interface.
+@end table
+@end defun
+
+@defun format-network-address address &optional omit-port
+This function converts the Lisp representation of a network address to
+a string.
+
+A five-element vector @code{[@var{a} @var{b} @var{c} @var{d} @var{p}]}
+represents an IPv4 address @var{a}.@var{b}.@var{c}.@var{d} and port
+number @var{p}. @code{format-network-address} converts that to the
+string @code{"@var{a}.@var{b}.@var{c}.@var{d}:@var{p}"}.
+
+A nine-element vector @code{[@var{a} @var{b} @var{c} @var{d} @var{e}
+@var{f} @var{g} @var{h} @var{p}]} represents an IPv6 address and port
+number. @code{format-network-address} converts that to the string
+@code{"[@var{a}:@var{b}:@var{c}:@var{d}:@var{e}:@var{f}:@var{g}:@var{h}]:@var{p}"}.
+
+If the vector does not include the port number, @var{p}, or if
+@var{omit-port} is non-@code{nil}, the result does not include the
+@code{:@var{p}} suffix.
+@end defun
+
+@node Byte Packing
+@section Packing and Unpacking Byte Arrays
+
+ This section describes how to pack and unpack arrays of bytes,
+usually for binary network protocols. These functions convert byte arrays
+to alists, and vice versa. The byte array can be represented as a
+unibyte string or as a vector of integers, while the alist associates
+symbols either with fixed-size objects or with recursive sub-alists.
+
+@cindex serializing
+@cindex deserializing
+@cindex packing
+@cindex unpacking
+ Conversion from byte arrays to nested alists is also known as
+@dfn{deserializing} or @dfn{unpacking}, while going in the opposite
+direction is also known as @dfn{serializing} or @dfn{packing}.
+
+@menu
+* Bindat Spec:: Describing data layout.
+* Bindat Functions:: Doing the unpacking and packing.
+* Bindat Examples:: Samples of what bindat.el can do for you!
+@end menu
+
+@node Bindat Spec
+@subsection Describing Data Layout
+
+ To control unpacking and packing, you write a @dfn{data layout
+specification}, a special nested list describing named and typed
+@dfn{fields}. This specification controls length of each field to be
+processed, and how to pack or unpack it.
+
+@cindex endianness
+@cindex big endian
+@cindex little endian
+@cindex network byte ordering
+ A field's @dfn{type} describes the size (in bytes) of the object
+that the field represents and, in the case of multibyte fields, how
+the bytes are ordered within the field. The two possible orderings
+are ``big endian'' (also known as ``network byte ordering'') and
+``little endian''. For instance, the number @code{#x23cd} (decimal
+9165) in big endian would be the two bytes @code{#x23} @code{#xcd};
+and in little endian, @code{#xcd} @code{#x23}. Here are the possible
+type values:
+
+@table @code
+@item u8
+@itemx byte
+Unsigned byte, with length 1.
+
+@item u16
+@itemx word
+@itemx short
+Unsigned integer in network byte order, with length 2.
+
+@item u24
+Unsigned integer in network byte order, with length 3.
+
+@item u32
+@itemx dword
+@itemx long
+Unsigned integer in network byte order, with length 4.
+Note: These values may be limited by Emacs' integer implementation limits.
+
+@item u16r
+@itemx u24r
+@itemx u32r
+Unsigned integer in little endian order, with length 2, 3 and 4, respectively.
+
+@item str @var{len}
+String of length @var{len}.
+
+@item strz @var{len}
+Zero-terminated string of length @var{len}.
+
+@item vec @var{len}
+Vector of @var{len} bytes.
+
+@item ip
+Four-byte vector representing an Internet address. For example:
+@code{[127 0 0 1]} for localhost.
+
+@item bits @var{len}
+List of set bits in @var{len} bytes. The bytes are taken in big
+endian order and the bits are numbered starting with @code{8 *
+@var{len} @minus{} 1} and ending with zero. For example: @code{bits
+2} unpacks @code{#x28} @code{#x1c} to @code{(2 3 4 11 13)} and
+@code{#x1c} @code{#x28} to @code{(3 5 10 11 12)}.
+
+@item (eval @var{form})
+@var{form} is a Lisp expression evaluated at the moment the field is
+unpacked or packed. The result of the evaluation should be one of the
+above-listed type specifications.
+@end table
+
+A field specification generally has the form @code{([@var{name}]
+@var{handler})}. The square braces indicate that @var{name} is
+optional. (Don't use names that are symbols meaningful as type
+specifications (above) or handler specifications (below), since that
+would be ambiguous.) @var{name} can be a symbol or the expression
+@code{(eval @var{form})}, in which case @var{form} should evaluate to
+a symbol.
+
+@var{handler} describes how to unpack or pack the field and can be one
+of the following:
+
+@table @code
+@item @var{type}
+Unpack/pack this field according to the type specification @var{type}.
+
+@item eval @var{form}
+Evaluate @var{form}, a Lisp expression, for side-effect only. If the
+field name is specified, the value is bound to that field name.
+@var{form} can access and update these dynamically bound variables:
+
+@table @code
+@item raw-data
+The data as a byte array.
+
+@item pos
+Current position of the unpacking or packing operation.
+
+@item struct
+Alist.
+
+@item last
+Value of the last field processed.
+@end table
+
+@item fill @var{len}
+Skip @var{len} bytes. In packing, this leaves them unchanged,
+which normally means they remain zero. In unpacking, this means
+they are ignored.
+
+@item align @var{len}
+Skip to the next multiple of @var{len} bytes.
+
+@item struct @var{spec-name}
+Process @var{spec-name} as a sub-specification. This describes a
+structure nested within another structure.
+
+@item union @var{form} (@var{tag} @var{spec})@dots{}
+@c ??? I don't see how one would actually use this.
+@c ??? what kind of expression would be useful for @var{form}?
+Evaluate @var{form}, a Lisp expression, find the first @var{tag}
+that matches it, and process its associated data layout specification
+@var{spec}. Matching can occur in one of three ways:
+
+@itemize
+@item
+If a @var{tag} has the form @code{(eval @var{expr})}, evaluate
+@var{expr} with the variable @code{tag} dynamically bound to the value
+of @var{form}. A non-@code{nil} result indicates a match.
+
+@item
+@var{tag} matches if it is @code{equal} to the value of @var{form}.
+
+@item
+@var{tag} matches unconditionally if it is @code{t}.
+@end itemize
+
+@item repeat @var{count} @var{field-spec}@dots{}
+@var{count} may be an integer, or a list of one element naming a
+previous field. For correct operation, each @var{field-spec} must
+include a name.
+@c ??? What does it MEAN?
+@end table
+
+@node Bindat Functions
+@subsection Functions to Unpack and Pack Bytes
+
+ In the following documentation, @var{spec} refers to a data layout
+specification, @code{raw-data} to a byte array, and @var{struct} to an
+alist representing unpacked field data.
+
+@defun bindat-unpack spec raw-data &optional pos
+This function unpacks data from the byte array @code{raw-data}
+according to @var{spec}. Normally this starts unpacking at the
+beginning of the byte array, but if @var{pos} is non-@code{nil}, it
+specifies a zero-based starting position to use instead.
+
+The value is an alist or nested alist in which each element describes
+one unpacked field.
+@end defun
+
+@defun bindat-get-field struct &rest name
+This function selects a field's data from the nested alist
+@var{struct}. Usually @var{struct} was returned by
+@code{bindat-unpack}. If @var{name} corresponds to just one argument,
+that means to extract a top-level field value. Multiple @var{name}
+arguments specify repeated lookup of sub-structures. An integer name
+acts as an array index.
+
+For example, if @var{name} is @code{(a b 2 c)}, that means to find
+field @code{c} in the third element of subfield @code{b} of field
+@code{a}. (This corresponds to @code{struct.a.b[2].c} in C.)
+@end defun
+
+@defun bindat-length spec struct
+@c ??? I don't understand this at all -- rms
+This function returns the length in bytes of @var{struct}, according
+to @var{spec}.
+@end defun
+
+@defun bindat-pack spec struct &optional raw-data pos
+This function returns a byte array packed according to @var{spec} from
+the data in the alist @var{struct}. Normally it creates and fills a
+new byte array starting at the beginning. However, if @var{raw-data}
+is non-@code{nil}, it specifies a pre-allocated string or vector to
+pack into. If @var{pos} is non-@code{nil}, it specifies the starting
+offset for packing into @code{raw-data}.
+
+@c ??? Isn't this a bug? Shouldn't it always be unibyte?
+Note: The result is a multibyte string; use @code{string-make-unibyte}
+on it to make it unibyte if necessary.
+@end defun
+
+@defun bindat-ip-to-string ip
+Convert the Internet address vector @var{ip} to a string in the usual
+dotted notation.
+
+@example
+(bindat-ip-to-string [127 0 0 1])
+ @result{} "127.0.0.1"
+@end example
+@end defun
+
+@node Bindat Examples
+@subsection Examples of Byte Unpacking and Packing
+
+ Here is a complete example of byte unpacking and packing:
+
+@lisp
+(defvar fcookie-index-spec
+ '((:version u32)
+ (:count u32)
+ (:longest u32)
+ (:shortest u32)
+ (:flags u32)
+ (:delim u8)
+ (:ignored fill 3)
+ (:offset repeat (:count)
+ (:foo u32)))
+ "Description of a fortune cookie index file's contents.")
+
+(defun fcookie (cookies &optional index)
+ "Display a random fortune cookie from file COOKIES.
+Optional second arg INDEX specifies the associated index
+filename, which is by default constructed by appending
+\".dat\" to COOKIES. Display cookie text in possibly
+new buffer \"*Fortune Cookie: BASENAME*\" where BASENAME
+is COOKIES without the directory part."
+ (interactive "fCookies file: ")
+ (let* ((info (with-temp-buffer
+ (insert-file-contents-literally
+ (or index (concat cookies ".dat")))
+ (bindat-unpack fcookie-index-spec
+ (buffer-string))))
+ (sel (random (bindat-get-field info :count)))
+ (beg (cdar (bindat-get-field info :offset sel)))
+ (end (or (cdar (bindat-get-field info
+ :offset (1+ sel)))
+ (nth 7 (file-attributes cookies)))))
+ (switch-to-buffer
+ (get-buffer-create
+ (format "*Fortune Cookie: %s*"
+ (file-name-nondirectory cookies))))
+ (erase-buffer)
+ (insert-file-contents-literally
+ cookies nil beg (- end 3))))
+
+(defun fcookie-create-index (cookies &optional index delim)
+ "Scan file COOKIES, and write out its index file.
+Optional second arg INDEX specifies the index filename,
+which is by default constructed by appending \".dat\" to
+COOKIES. Optional third arg DELIM specifies the unibyte
+character which, when found on a line of its own in
+COOKIES, indicates the border between entries."
+ (interactive "fCookies file: ")
+ (setq delim (or delim ?%))
+ (let ((delim-line (format "\n%c\n" delim))
+ (count 0)
+ (max 0)
+ min p q len offsets)
+ (unless (= 3 (string-bytes delim-line))
+ (error "Delimiter cannot be represented in one byte"))
+ (with-temp-buffer
+ (insert-file-contents-literally cookies)
+ (while (and (setq p (point))
+ (search-forward delim-line (point-max) t)
+ (setq len (- (point) 3 p)))
+ (setq count (1+ count)
+ max (max max len)
+ min (min (or min max) len)
+ offsets (cons (1- p) offsets))))
+ (with-temp-buffer
+ (set-buffer-multibyte nil)
+ (insert
+ (string-make-unibyte
+ (bindat-pack
+ fcookie-index-spec
+ `((:version . 2)
+ (:count . ,count)
+ (:longest . ,max)
+ (:shortest . ,min)
+ (:flags . 0)
+ (:delim . ,delim)
+ (:offset . ,(mapcar (lambda (o)
+ (list (cons :foo o)))
+ (nreverse offsets)))))))
+ (let ((coding-system-for-write 'raw-text-unix))
+ (write-file (or index (concat cookies ".dat")))))))
+@end lisp
+
+Following is an example of defining and unpacking a complex structure.
+Consider the following C structures:
+
+@example
+struct header @{
+ unsigned long dest_ip;
+ unsigned long src_ip;
+ unsigned short dest_port;
+ unsigned short src_port;
+@};
+
+struct data @{
+ unsigned char type;
+ unsigned char opcode;
+ unsigned long length; /* In little endian order */
+ unsigned char id[8]; /* null-terminated string */
+ unsigned char data[/* (length + 3) & ~3 */];
+@};
+
+struct packet @{
+ struct header header;
+ unsigned char items;
+ unsigned char filler[3];
+ struct data item[/* items */];
+
+@};
+@end example
+
+The corresponding data layout specification:
+
+@lisp
+(setq header-spec
+ '((dest-ip ip)
+ (src-ip ip)
+ (dest-port u16)
+ (src-port u16)))
+
+(setq data-spec
+ '((type u8)
+ (opcode u8)
+ (length u16r) ;; little endian order
+ (id strz 8)
+ (data vec (length))
+ (align 4)))
+
+(setq packet-spec
+ '((header struct header-spec)
+ (items u8)
+ (fill 3)
+ (item repeat (items)
+ (struct data-spec))))
+@end lisp
+
+A binary data representation:
+
+@lisp
+(setq binary-data
+ [ 192 168 1 100 192 168 1 101 01 28 21 32 2 0 0 0
+ 2 3 5 0 ?A ?B ?C ?D ?E ?F 0 0 1 2 3 4 5 0 0 0
+ 1 4 7 0 ?B ?C ?D ?E ?F ?G 0 0 6 7 8 9 10 11 12 0 ])
+@end lisp
+
+The corresponding decoded structure:
+
+@lisp
+(setq decoded (bindat-unpack packet-spec binary-data))
+ @result{}
+((header
+ (dest-ip . [192 168 1 100])
+ (src-ip . [192 168 1 101])
+ (dest-port . 284)
+ (src-port . 5408))
+ (items . 2)
+ (item ((data . [1 2 3 4 5])
+ (id . "ABCDEF")
+ (length . 5)
+ (opcode . 3)
+ (type . 2))
+ ((data . [6 7 8 9 10 11 12])
+ (id . "BCDEFG")
+ (length . 7)
+ (opcode . 4)
+ (type . 1))))
+@end lisp
+
+Fetching data from this structure:
+
+@lisp
+(bindat-get-field decoded 'item 1 'id)
+ @result{} "BCDEFG"
+@end lisp
+
+@ignore
+ arch-tag: ba9da253-e65f-4e7f-b727-08fba0a1df7a
+@end ignore