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 "m_rand.h"
  11 #include "message_id.h"
  12 #include <sys/time.h>  /* for gettimeofday() */
  13
  14
  15 static enum {
  16   NMH_MESSAGE_ID_LOCALNAME,
  17   NMH_MESSAGE_ID_RANDOM
  18 } message_id_style = NMH_MESSAGE_ID_LOCALNAME;
  19 static char message_id_[BUFSIZ];
  20
  21
  22 /* Convert name of message id style to integer value and store it. */
  23 int
  24 save_message_id_style (const char *value) {
  25   if (! strcasecmp (value, "localname")) {
  26     message_id_style = NMH_MESSAGE_ID_LOCALNAME;
  27     return 0;
  28   }
  29   if (! strcasecmp (value, "random")) {
  30     message_id_style = NMH_MESSAGE_ID_RANDOM;
  31     return 0;
  32   }
  33   return 1;
  34 }
  35
  36
  37 char *
  38 message_id (time_t tclock, int content_id) {
  39   switch (message_id_style) {
  40     case NMH_MESSAGE_ID_LOCALNAME: {
  41       char *format = content_id  ?  "<%d.%ld.%%d@%s>"  :  "<%d.%ld@%s>";
  42
  43       snprintf (message_id_, sizeof message_id_, format,
  44                 (int) getpid (), (long) tclock, LocalName (1));
  45
  46       break;
  47     }
  48
  49     case NMH_MESSAGE_ID_RANDOM: {
  50       char *format = content_id
  51         ?  "<%d-%ld.%06ld%%d@%.*s.%.*s.%.*s>"
  52         :  "<%d-%ld.%06ld@%.*s.%.*s.%.*s>";
  53       /* Use a sequence of digits divisible by 3 because that will
  54          expand to base64 without any waste.  Must be shorter than 58,
  55          see below. */
  56       unsigned char rnd[9];
  57       /* The part after the '@' is divided into thirds.  The base64
  58          encoded string will be 4/3 the size of rnd. */
  59       size_t one_third = sizeof rnd * 4/3/3;
  60
  61       if (m_rand (rnd, sizeof rnd) == 0) {
  62         struct timeval now;
  63         /* All we really need is 4 * [sizeof rnd/3] + 2, as long as
  64            the base64 encoding stays shorter than 76 bytes so embedded
  65            newlines aren't necessary.  But use double the sizeof rnd
  66            just to be safe. */
  67         unsigned char rnd_base64[2 * sizeof rnd];
  68         unsigned char *cp;
  69         int i;
  70
  71         writeBase64 (rnd, sizeof rnd, rnd_base64);
  72
  73         for (i = strlen ((const char *) rnd_base64) - 1;
  74              i > 0  &&  iscntrl (rnd_base64[i]);
  75              --i) {
  76           /* Remove trailing newline.  rnd_base64 had better be
  77              shorter than 76 characters, so don't bother to look for
  78              embedded newlines. */
  79           rnd_base64[i] = '\0';
  80         }
  81
  82         /* Try to make the base64 string look a little more like a
  83            hostname by replacing + with - and / with _. */
  84         for (cp = rnd_base64; *cp; ++cp) {
  85           if (*cp == '+') {
  86             *cp = '-';
  87           } else if (*cp == '/') {
  88             *cp = '_';
  89           }
  90         }
  91
  92         /* gettimeofday() and getpid() shouldn't fail on POSIX platforms. */
  93         gettimeofday (&now, 0);
  94
  95         /* The format string inserts a couple of dots, for the benefit
  96            of spam filters that want to see a message id with a final
  97            part that resembles a hostname. */
  98         snprintf (message_id_, sizeof message_id_, format,
  99                   getpid (), (long) now.tv_sec, (long) now.tv_usec,
 100                   one_third, rnd_base64,
 101                   one_third, &rnd_base64[one_third],
 102                   one_third, &rnd_base64[2*one_third]);
 103       }
 104
 105       break;
 106     }
 107   }
 108
 109   return message_id_;
 110 }