stdio-redirect.h

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/*
 * Copyright (C) 2014 Chris Johns (chrisj@rtems.org)
 *
 * The license and distribution terms for this file may be
 * found in the file LICENSE in this distribution.
 *
 * This software with is provided ``as is'' and with NO WARRANTY.
 */

/*
 * @brief Redirect an stdio file decriptor.
 *
 * The is a helper module of code design to redirect an stdio file
 * descriptor. You can optionally have the data buffered and/or you can provide
 * a handler function that is called when data arrives.
 *
 * The module uses standard POSIX calls to implement the redirection and if the
 * threading was POSIX based the code would be portable. Currently the code
 * uses RTEMS threads.
 *
 * Redirecting stderr and stdout is useful in embedded system because you can
 * transport the output off your device or create a web interface that can
 * display the output. This can be a very powerful diagnostic and support tool.
 *
 * The implementation does:
 *
 *  1. Duplicate the file descriptor (fd) to redirect using the dup call. The
 *     duplicated desciptor is used to echo the output out the existing path.
 *
 *  2. Create a pipe using the pipe call.
 *
 *  3. Duplicate the pipe's writer file descriptor to user's file
 *     descriptor. This results in any writes to the user's fd being written to
 *     the pipe.
 *
 *  4. Create a reader task that blocks on the pipe. It optionally calls a
 *     handler and if configured buffers the data.
 */

#if !defined(RTEMS_STDIO_REDIRECT_H)
#define RTEMS_STDIO_REDIRECT_H

#include <stdbool.h>
#include <rtems.h>

#ifdef __cplusplus
extern "C" {
#endif /* __cplusplus */

/*
 * Handler called whenever redirected data arrives.
 *
 * @param buffer The data.
 * @param length The amount of data in the buffer.
 */
typedef void (*rtems_stdio_redirect_handler)(const char* buffer,
                                             ssize_t     length);

/*
 * Redirector data.
 */
typedef struct
{
  volatile uint32_t            state;       
  rtems_id                     reader;      
  rtems_id                     lock;        
  int                          fd;          
  int                          fd_dup;      
  int                          pipe[2];     
  char*                        input;       
  ssize_t                      input_size;  
  char*                        buffer;      
  ssize_t                      buffer_size; 
  ssize_t                      in;          
  bool                         full;        
  bool                         echo;        
  rtems_stdio_redirect_handler handler;     
} rtems_stdio_redirect;

/*
 * Open a redirector returning the handle to it.
 *
 * @param fd The file descriptor to redirect.
 * @param priority The priority of the reader thread.
 */
rtems_stdio_redirect* rtems_stdio_redirect_open(int                          fd,
                                                rtems_task_priority          priority,
                                                size_t                       stack_size,
                                                ssize_t                      input_size,
                                                ssize_t                      buffer_size,
                                                bool                         echo,
                                                rtems_stdio_redirect_handler handler);

/*
 * Close the redirector.
 */
void rtems_stdio_redirect_close(rtems_stdio_redirect* sr);

/*
 * Get data from the capture buffer. Data read is removed from the buffer.
 *
 * @param sr The stdio redirection handle.
 * @param buffer The buffer data is written into.
 * @param length The size of the buffer.
 * @return ssize_t The amount of data written and -1 or an error.
 */
ssize_t rtems_stdio_redirect_read(rtems_stdio_redirect* sr,
                                  char*                 buffer,
                                  ssize_t               length);

#ifdef __cplusplus
}
#endif /* __cplusplus */

#endif