--- /dev/null
+/* Filtering of data through a subprocess.
+ Copyright (C) 2009 Free Software Foundation, Inc.
+ Written by Bruno Haible <haible@clisp.cons.org>, 2009,
+ and Paolo Bonzini <bonzini@gnu.org>, 2009.
+
+ This program is free software: you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 3 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <http://www.gnu.org/licenses/>. */
+
+#ifndef _PIPE_FILTER_H
+#define _PIPE_FILTER_H
+
+#include <stdbool.h>
+#include <stddef.h>
+
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+
+/* Piping data through a subprocess in the naïve way - write data to the
+ subprocess and read from the subprocess when you expect it to have
+ produced results - is subject to two kinds of deadlocks:
+ 1) If you write more than PIPE_MAX bytes or, more generally, if you write
+ more bytes than the subprocess can handle at once, the subprocess
+ may write its data and wait on you to read it, but you are currently
+ busy writing.
+ 2) When you don't know ahead of time how many bytes the subprocess
+ will produce, the usual technique of calling read (fd, buf, BUFSIZ)
+ with a fixed BUFSIZ will, on Linux 2.2.17 and on BSD systems, cause
+ the read() call to block until *all* of the buffer has been filled.
+ But the subprocess cannot produce more data until you gave it more
+ input. But you are currently busy reading from it.
+
+ This header file declares four set of functions that pipes data through
+ the subprocess, without risking these deadlocks.
+
+ The side that writes data to the subprocess can be seen as a "generator",
+ that is, as a subroutine that produces and writes a piece of data here and
+ there, see <http://en.wikipedia.org/wiki/Generator_(computer_science)>.
+ But often, it can be written in the form of an "iterator", that is, as a
+ function that, each time it is invoked, produces and writes one more piece
+ of data.
+
+ Similarly, the side that reads data from the subprocess can be seen as
+ a "generator", that is, as a subroutine that consumes a piece of data here
+ and there. Often, it can be written in the form of an "iterator", that
+ is, as a function that, each time it is invoked, consumes one more piece
+ of data.
+
+ This header file declares four set of functions:
+
+ | writer | reader |
+ ----------------+------------+------------+
+ pipe_filter_ii | iterator | iterator |
+ pipe_filter_ig | iterator | generator |
+ pipe_filter_gi | generator | iterator |
+ pipe_filter_gg | generator | generator |
+ ----------------+------------+------------+
+
+ The last one uses threads in order to implement two generators running at
+ the same time. (For the relation between generators, coroutines, and
+ threads, see <http://en.wikipedia.org/wiki/Generator_(computer_science)>
+ and <http://en.wikipedia.org/wiki/Coroutine>.) It is therefore only
+ portable to platforms with kernel-based POSIX threads. */
+
+/* These two functions together describe the side that writes data to the
+ subprocess when it has the form of an iterator.
+ - prepare_write (&num_bytes, p) must either return a pointer to data that
+ is ready to be written and set num_bytes to the number of bytes ready to
+ be written, or return NULL when no more bytes are to be written.
+ - done_write (data_written, num_bytes_written) is called after
+ num_bytes_written bytes were written. It is guaranteed that
+ num_bytes_written > 0.
+ Here p is always the private_data argument passed to the main function. */
+typedef const void * (*prepare_write_fn) (size_t *num_bytes_p,
+ void *private_data);
+typedef void (*done_write_fn) (void *data_written, size_t num_bytes_written,
+ void *private_data);
+
+/* These two functions together describe the side that reads data from the
+ subprocess when it has the form of an iterator.
+ - prepare_read (&num_bytes, p) must return a pointer to a buffer for data
+ that can be read and set num_bytes to the size of that buffer
+ (must be > 0).
+ - done_read (data_read, num_bytes_read, p) is called after num_bytes_read
+ bytes were read into the buffer.
+ Here p is always the private_data argument passed to the main function. */
+typedef void * (*prepare_read_fn) (size_t *num_bytes_p,
+ void *private_data);
+typedef void (*done_read_fn) (void *data_read, size_t num_bytes_read,
+ void *private_data);
+
+
+/* ============================ pipe_filter_ii ============================ */
+
+/* Create a subprocess and pipe some data through it.
+ Arguments:
+ - progname is the program name used in error messages.
+ - prog_path is the file name of the program to invoke.
+ - prog_argv is a NULL terminated argument list, starting with prog_path as
+ first element.
+ - If null_stderr is true, the subprocess' stderr will be redirected to
+ /dev/null, and the usual error message to stderr will be omitted.
+ This is suitable when the subprocess does not fulfill an important task.
+ - If exit_on_error is true, any error will cause the main process to exit
+ with an error status.
+ If the subprocess does not terminate correctly, exit if exit_on_error is
+ true, otherwise return 127.
+ Callback arguments are as described above.
+
+ Data is alternatingly written to the subprocess, through the functions
+ prepare_write and done_write, and read from the subprocess, through the
+ functions prepare_read and done_read.
+
+ Note that the prepare_write/done_write functions and the
+ prepare_read/done_read functions may be called in different threads than
+ the current thread (depending on the platform). But they will not be
+ called after the pipe_filter_ii_execute function has returned.
+
+ Return 0 upon success, or (only if exit_on_error is false):
+ - -1 with errno set upon failure,
+ - the positive exit code of the subprocess if that failed. */
+extern int
+ pipe_filter_ii_execute (const char *progname,
+ const char *prog_path, const char **prog_argv,
+ bool null_stderr, bool exit_on_error,
+ prepare_write_fn prepare_write,
+ done_write_fn done_write,
+ prepare_read_fn prepare_read,
+ done_read_fn done_read,
+ void *private_data);
+
+
+/* ============================ pipe_filter_ig ============================ */
+
+struct pipe_filter_ig;
+
+
+/* ============================ pipe_filter_gi ============================ */
+
+struct pipe_filter_gi;
+
+/* Create a subprocess and pipe some data through it.
+ Arguments:
+ - progname is the program name used in error messages.
+ - prog_path is the file name of the program to invoke.
+ - prog_argv is a NULL terminated argument list, starting with
+ prog_path as first element.
+ - If null_stderr is true, the subprocess' stderr will be redirected
+ to /dev/null, and the usual error message to stderr will be
+ omitted. This is suitable when the subprocess does not fulfill an
+ important task.
+ - If exit_on_error is true, any error will cause the main process to
+ exit with an error status.
+ If the subprocess does not start correctly, exit if exit_on_error is
+ true, otherwise return NULL and set errno.
+
+ The caller will write to the subprocess through pipe_filter_gi_write
+ and finally call pipe_filter_gi_write. During such calls, the
+ prepare_read and done_read function may be called to process any data
+ that the subprocess has written.
+
+ Note that the prepare_read/done_read functions may be called in a
+ different thread than the current thread (depending on the platform).
+ But they will not be called after the pipe_filter_gi_close function has
+ returned.
+
+ Return the freshly created 'struct pipe_filter_gi'. */
+extern struct pipe_filter_gi *
+ pipe_filter_gi_create (const char *progname,
+ const char *prog_path, const char **prog_argv,
+ bool null_stderr, bool exit_on_error,
+ prepare_read_fn prepare_read,
+ done_read_fn done_read,
+ void *private_data);
+
+/* Write size bytes starting at buf into the pipe and in the meanwhile
+ possibly call the prepare_read and done_read functions specified to
+ pipe_filter_gi_create.
+
+ Note that the prepare_read/done_read functions may be called in a
+ different thread than the current thread (depending on the platform).
+ However, they will always be called before pipe_filter_gi_write has
+ returned, or otherwise not sooner than the next call to
+ pipe_filter_gi_write or pipe_filter_gi_close.
+
+ Return only after all the entire buffer has been written to the pipe or
+ the subprocess has exited.
+
+ Return 0 upon success, or (only if exit_on_error is false):
+ - -1 with errno set upon failure,
+ - the positive exit code of the subprocess if that failed. */
+extern int
+ pipe_filter_gi_write (struct pipe_filter_gi *filter,
+ const void *buf, size_t size);
+
+/* Finish reading the output via the prepare_read/done_read functions
+ specified to pipe_filter_gi_create.
+
+ Note that the prepare_read/done_read functions may be called in a
+ different thread than the current thread (depending on the platform).
+ However, they will always be called before pipe_filter_gi_close has
+ returned.
+
+ The write side of the pipe is closed as soon as pipe_filter_gi_close
+ starts, while the read side will be closed just before it finishes.
+
+ Return 0 upon success, or (only if exit_on_error is false):
+ - -1 with errno set upon failure,
+ - the positive exit code of the subprocess if that failed. */
+extern int
+ pipe_filter_gi_close (struct pipe_filter_gi *filter);
+
+
+/* ============================ pipe_filter_gg ============================ */
+
+
+/* ======================================================================== */
+
+
+#ifdef __cplusplus
+}
+#endif
+
+
+#endif /* _PIPE_FILTER_H */
projects / gnulib.git / blobdiff