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

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