cups/backchannel.c

   1 /*
   2  * Backchannel functions for CUPS.
   3  *
   4  * Copyright 2007-2014 by Apple Inc.
   5  * Copyright 1997-2007 by Easy Software Products.
   6  *
   7  * Licensed under Apache License v2.0.  See the file "LICENSE" for more information.
   8  */
   9
  10 /*
  11  * Include necessary headers...
  12  */
  13
  14 #include "cups.h"
  15 #include <errno.h>
  16 #ifdef _WIN32
  17 #  include <io.h>
  18 #  include <fcntl.h>
  19 #else
  20 #  include <sys/time.h>
  21 #endif /* _WIN32 */
  22
  23
  24 /*
  25  * Local functions...
  26  */
  27
  28 static void     cups_setup(fd_set *set, struct timeval *tval,
  29                            double timeout);
  30
  31
  32 /*
  33  * 'cupsBackChannelRead()' - Read data from the backchannel.
  34  *
  35  * Reads up to "bytes" bytes from the backchannel/backend. The "timeout"
  36  * parameter controls how many seconds to wait for the data - use 0.0 to
  37  * return immediately if there is no data, -1.0 to wait for data indefinitely.
  38  *
  39  * @since CUPS 1.2/macOS 10.5@
  40  */
  41
  42 ssize_t                                 /* O - Bytes read or -1 on error */
  43 cupsBackChannelRead(char   *buffer,     /* I - Buffer to read into */
  44                     size_t bytes,       /* I - Bytes to read */
  45                     double timeout)     /* I - Timeout in seconds, typically 0.0 to poll */
  46 {
  47   fd_set        input;                  /* Input set */
  48   struct timeval tval;                  /* Timeout value */
  49   int           status;                 /* Select status */
  50
  51
  52  /*
  53   * Wait for input ready.
  54   */
  55
  56   do
  57   {
  58     cups_setup(&input, &tval, timeout);
  59
  60     if (timeout < 0.0)
  61       status = select(4, &input, NULL, NULL, NULL);
  62     else
  63       status = select(4, &input, NULL, NULL, &tval);
  64   }
  65   while (status < 0 && errno != EINTR && errno != EAGAIN);
  66
  67   if (status < 0)
  68     return (-1);                        /* Timeout! */
  69
  70  /*
  71   * Read bytes from the pipe...
  72   */
  73
  74 #ifdef _WIN32
  75   return ((ssize_t)_read(3, buffer, (unsigned)bytes));
  76 #else
  77   return (read(3, buffer, bytes));
  78 #endif /* _WIN32 */
  79 }
  80
  81
  82 /*
  83  * 'cupsBackChannelWrite()' - Write data to the backchannel.
  84  *
  85  * Writes "bytes" bytes to the backchannel/filter. The "timeout" parameter
  86  * controls how many seconds to wait for the data to be written - use
  87  * 0.0 to return immediately if the data cannot be written, -1.0 to wait
  88  * indefinitely.
  89  *
  90  * @since CUPS 1.2/macOS 10.5@
  91  */
  92
  93 ssize_t                                 /* O - Bytes written or -1 on error */
  94 cupsBackChannelWrite(
  95     const char *buffer,                 /* I - Buffer to write */
  96     size_t     bytes,                   /* I - Bytes to write */
  97     double     timeout)                 /* I - Timeout in seconds, typically 1.0 */
  98 {
  99   fd_set        output;                 /* Output set */
 100   struct timeval tval;                  /* Timeout value */
 101   int           status;                 /* Select status */
 102   ssize_t       count;                  /* Current bytes */
 103   size_t        total;                  /* Total bytes */
 104
 105
 106  /*
 107   * Write all bytes...
 108   */
 109
 110   total = 0;
 111
 112   while (total < bytes)
 113   {
 114    /*
 115     * Wait for write-ready...
 116     */
 117
 118     do
 119     {
 120       cups_setup(&output, &tval, timeout);
 121
 122       if (timeout < 0.0)
 123         status = select(4, NULL, &output, NULL, NULL);
 124       else
 125         status = select(4, NULL, &output, NULL, &tval);
 126     }
 127     while (status < 0 && errno != EINTR && errno != EAGAIN);
 128
 129     if (status <= 0)
 130       return (-1);                      /* Timeout! */
 131
 132    /*
 133     * Write bytes to the pipe...
 134     */
 135
 136 #ifdef _WIN32
 137     count = (ssize_t)_write(3, buffer, (unsigned)(bytes - total));
 138 #else
 139     count = write(3, buffer, bytes - total);
 140 #endif /* _WIN32 */
 141
 142     if (count < 0)
 143     {
 144      /*
 145       * Write error - abort on fatal errors...
 146       */
 147
 148       if (errno != EINTR && errno != EAGAIN)
 149         return (-1);
 150     }
 151     else
 152     {
 153      /*
 154       * Write succeeded, update buffer pointer and total count...
 155       */
 156
 157       buffer += count;
 158       total  += (size_t)count;
 159     }
 160   }
 161
 162   return ((ssize_t)bytes);
 163 }
 164
 165
 166 /*
 167  * 'cups_setup()' - Setup select()
 168  */
 169
 170 static void
 171 cups_setup(fd_set         *set,         /* I - Set for select() */
 172            struct timeval *tval,        /* I - Timer value */
 173            double         timeout)      /* I - Timeout in seconds */
 174 {
 175   tval->tv_sec = (int)timeout;
 176   tval->tv_usec = (int)(1000000.0 * (timeout - tval->tv_sec));
 177
 178   FD_ZERO(set);
 179   FD_SET(3, set);
 180 }