diplodocus.org Git - nmh/blob - sbr/message_id.c

   1 /*
   2  * message-id.c -- construct the body of a Message-ID or Content-ID
   3  *                 header field
   4  *
   5  * This code is Copyright (c) 2012, by the authors of nmh.  See the
   6  * COPYRIGHT file in the root directory of the nmh distribution for
   7  * complete copyright information.
   8  */
   9
  10 #include <h/mh.h>
  11 #include <sys/time.h>  /* for gettimeofday() */
  12
  13
  14 static enum {
  15   NMH_MESSAGE_ID_LOCALNAME,
  16   NMH_MESSAGE_ID_RANDOM
  17 } message_id_style = NMH_MESSAGE_ID_LOCALNAME;
  18 static char message_id_[BUFSIZ];
  19
  20
  21 /* Convert name of message id style to integer value and store it. */
  22 int
  23 save_message_id_style (const char *value) {
  24   if (! strcasecmp (value, "localname")) {
  25     message_id_style = NMH_MESSAGE_ID_LOCALNAME;
  26     return 0;
  27   }
  28   if (! strcasecmp (value, "random")) {
  29     message_id_style = NMH_MESSAGE_ID_RANDOM;
  30     return 0;
  31   }
  32   return 1;
  33 }
  34
  35
  36 char *
  37 message_id (time_t tclock, int content_id) {
  38   switch (message_id_style) {
  39     case NMH_MESSAGE_ID_LOCALNAME: {
  40       char *format = content_id  ?  "<%d.%ld.%%d@%s>"  :  "<%d.%ld@%s>";
  41
  42       snprintf (message_id_, sizeof message_id_, format,
  43                 (int) getpid (), (long) tclock, LocalName (1));
  44
  45       break;
  46     }
  47
  48     case NMH_MESSAGE_ID_RANDOM: {
  49       char *format = content_id
  50         ?  "<%d-%ld.%06ld%%d@%.*s.%.*s.%.*s>"
  51         :  "<%d-%ld.%06ld@%.*s.%.*s.%.*s>";
  52       /* Use a sequence of digits divisible by 3 because that will
  53          expand to base64 without any waste.  Must be shorter than 58,
  54          see below. */
  55       unsigned char rnd[9];
  56       /* The part after the '@' is divided into thirds.  The base64
  57          encoded string will be 4/3 the size of rnd. */
  58       size_t one_third = sizeof rnd * 4/3/3;
  59
  60       if (m_rand (rnd, sizeof rnd) == 0) {
  61         struct timeval now;
  62         /* All we really need is 4 * [sizeof rnd/3] + 2, as long as
  63            the base64 encoding stays shorter than 76 bytes so embedded
  64            newlines aren't necessary.  But use double the sizeof rnd
  65            just to be safe. */
  66         unsigned char rnd_base64[2 * sizeof rnd];
  67         unsigned char *cp;
  68         int i;
  69
  70         writeBase64 (rnd, sizeof rnd, rnd_base64);
  71
  72         for (i = strlen ((const char *) rnd_base64) - 1;
  73              i > 0  &&  iscntrl (rnd_base64[i]);
  74              --i) {
  75           /* Remove trailing newline.  rnd_base64 had better be
  76              shorter than 76 characters, so don't bother to look for
  77              embedded newlines. */
  78           rnd_base64[i] = '\0';
  79         }
  80
  81         /* Try to make the base64 string look a little more like a
  82            hostname by replacing + with - and / with _. */
  83         for (cp = rnd_base64; *cp; ++cp) {
  84           if (*cp == '+') {
  85             *cp = '-';
  86           } else if (*cp == '/') {
  87             *cp = '_';
  88           }
  89         }
  90
  91         /* gettimeofday() and getpid() shouldn't fail on POSIX platforms. */
  92         gettimeofday (&now, 0);
  93
  94         /* The format string inserts a couple of dots, for the benefit
  95            of spam filters that want to see a message id with a final
  96            part that resembles a hostname. */
  97         snprintf (message_id_, sizeof message_id_, format,
  98                   getpid (), (long) now.tv_sec, (long) now.tv_usec,
  99                   one_third, rnd_base64,
 100                   one_third, &rnd_base64[one_third],
 101                   one_third, &rnd_base64[2*one_third]);
 102       }
 103
 104       break;
 105     }
 106   }
 107
 108   return message_id_;
 109 }