vlc_process.h

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// SPDX-License-Identifier: LGPL-2.1-or-later
/*****************************************************************************
 * vlc_process.h: vlc_process functions
 *****************************************************************************
 * Copyright © 2025 Videolabs, VideoLAN and VLC authors
 *
 * Authors: Gabriel Lafond Thenaille <gabriel@videolabs.io>
 *****************************************************************************/
 
#ifndef VLC_PROCESS_H
#define VLC_PROCESS_H
 
#include <vlc_common.h>
#include <vlc_tick.h>
 
/**
 * @ingroup misc
 * @file
 * VLC_PROCESS API
 * @defgroup process Process API
 * @{
 */
 
/**
 * Spawn a new process with input and output redirection.
 *
 * Creates and starts a new vlc_process for the specified executable path with
 * the given arguments. Sets up pipes to allow reading from the process's
 * standard output and writing to its standard input.
 *
 * @param [in]  path    Path to the executable to run. Must not be NULL.
 * @param [in]  argc    Number of arguments passed to the process (must be
 *                      greater than or equal to 0).
 * @param [in]  argv    Array of argument strings. May be NULL if argc is 0;
 *                      otherwise argv[0] must not be NULL.
 *
 * @return      A pointer to the newly created vlc_process structure on
 *              success, or NULL on failure.
 */
VLC_API struct vlc_process *
vlc_process_Spawn(const char *path, int argc, const char *const *argv);
 
/**
 * Kill a process and abort its I/O.
 *
 * Sends a termination signal to the process and shuts down the communication
 * channel, so that any in-flight or subsequent I/O on @p process completes
 * promptly instead of blocking: vlc_process_fd_Read() reports end-of-stream
 * and vlc_process_fd_Write() fails with EPIPE.
 *
 * This does not free @p process: vlc_process_Terminate() must still be called
 * for that. It can be called multiple times.
 *
 * @param [in]  process     Pointer to the vlc_process instance. Must not be
 *                          NULL.
 */
VLC_API void
vlc_process_Kill(struct vlc_process *process);
 
/**
 * Stop a vlc_process and wait for its termination.
 *
 * Closes its file descriptors, and waits for it to exit. Optionally sends a
 * termination signal to the process,
 *
 * @warning This must not be called concurrently with vlc_process_fd_Read() or
 *          vlc_process_fd_Write() on the same @p process. It closes the
 *          underlying pipe/socket and frees @p process, so the caller must
 *          ensure that any thread performing I/O has returned first to avoid a
 *          use-after-free. Use vlc_process_Kill() to unblock such a thread,
 *          then join it before calling this.
 *
 * @param [in]  process        Pointer to the vlc_process instance. Must not
 *                             be NULL.
 * @param [in]  kill_process   Whether to forcibly terminate the process
 *                             before waiting.
 *
 * @return      The exit status of the process, or -1 on error.
 */
VLC_API int
vlc_process_Terminate(struct vlc_process *process, bool kill_process);
 
/**
 * Read data from the process's standard output with a timeout.
 *
 * Attempts to read up to @p size bytes from the process's standard output
 * into the provided buffer, waiting up to @p timeout_ms milliseconds for data
 * to become available.
 *
 * On POSIX systems, this uses poll to wait for readability. On Windows,
 * a platform-specific implementation is used due to limitations with poll on
 * non-socket handles.
 *
 * @warning At most one thread may call this function on a given @p process at
 *          a time. Reading from one thread while another one writes is
 *          supported, but two concurrent readers are not.
 *
 * @param [in]  process     Pointer to the vlc_process instance.
 * @param [out] buf         Buffer where the read data will be stored.
 * @param [in]  size        Maximum number of bytes to read.
 * @param [in]  timeout_ms  Timeout in milliseconds to wait for data.
 *
 * @return      The number of bytes read on success,
 *              -1 on error, and errno is set to indicate the error.
 */
VLC_API ssize_t
vlc_process_fd_Read(struct vlc_process *process, uint8_t *buf, size_t size,
                    vlc_tick_t timeout_ms);
 
/**
 * Write data to the process's standard input with a timeout.
 *
 * Attempts to write up to @p size bytes from the provided buffer to the
 * process's standard input, waiting up to @p timeout_ms milliseconds for the
 * pipe to become writable.
 *
 * On POSIX systems, this uses poll to wait for writability. On Windows,
 * a platform-specific implementation is used due to limitations with poll on
 * non-socket handles.
 *
 * @warning At most one thread may call this function on a given @p process at
 *          a time. Writing from one thread while another one reads is
 *          supported, but two concurrent writers are not.
 *
 * @param [in]  process     Pointer to the vlc_process instance.
 * @param [in]  buf         Buffer containing the data to write.
 * @param [in]  size        Number of bytes to write.
 * @param [in]  timeout_ms  Timeout in milliseconds to wait for the pipe to be
 *                          writable.
 *
 * @return      The number of bytes written on success,
 *              -1 on error, and errno is set to indicate the error.
 */
VLC_API ssize_t
vlc_process_fd_Write(struct vlc_process *process, const uint8_t *buf, size_t size,
                     vlc_tick_t timeout_ms);
 
/**
 * @} process
 */
 
#endif /* VLC_PROCESS_H */