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 #include "base64.h"
  14
  15
  16 static enum {
  17   NMH_MESSAGE_ID_LOCALNAME,
  18   NMH_MESSAGE_ID_RANDOM
  19 } message_id_style = NMH_MESSAGE_ID_LOCALNAME;
  20 static char message_id_[BUFSIZ];
  21
  22
  23 /* Convert name of message id style to integer value and store it. */
  24 int
  25 save_message_id_style (const char *value)
  26 {
  27   if (! strcasecmp (value, "localname")) {
  28     message_id_style = NMH_MESSAGE_ID_LOCALNAME;
  29     return 0;
  30   }
  31   if (! strcasecmp (value, "random")) {
  32     message_id_style = NMH_MESSAGE_ID_RANDOM;
  33     return 0;
  34   }
  35   return 1;
  36 }
  37
  38
  39 char *
  40 message_id (time_t tclock, int content_id)
  41 {
  42   switch (message_id_style) {
  43     case NMH_MESSAGE_ID_LOCALNAME: {
  44 #define P(fmt) \
  45     snprintf(message_id_, sizeof message_id_, \
  46         (fmt), (int)getpid(), (long)tclock, LocalName(1))
  47
  48             if (content_id)
  49                 P("<%d.%ld.%%d@%s>");
  50             else
  51                 P("<%d.%ld@%s>");
  52 #undef P
  53       break;
  54     }
  55
  56     case NMH_MESSAGE_ID_RANDOM: {
  57       /* Use a sequence of digits divisible by 3 because that will
  58          expand to base64 without any waste.  Must be shorter than 58,
  59          see below. */
  60       unsigned char rnd[9];
  61       /* The part after the '@' is divided into thirds.  The base64
  62          encoded string will be 4/3 the size of rnd. */
  63       size_t one_third = sizeof rnd * 4/3/3;
  64
  65       if (m_rand (rnd, sizeof rnd) == 0) {
  66         struct timeval now;
  67         /* All we really need is 4 * [sizeof rnd/3] + 2, as long as
  68            the base64 encoding stays shorter than 76 bytes so embedded
  69            newlines aren't necessary.  But use double the sizeof rnd
  70            just to be safe. */
  71         unsigned char rnd_base64[2 * sizeof rnd];
  72         unsigned char *cp;
  73         int i;
  74
  75         writeBase64 (rnd, sizeof rnd, rnd_base64);
  76
  77         for (i = strlen ((const char *) rnd_base64) - 1;
  78              i > 0  &&  iscntrl (rnd_base64[i]);
  79              --i) {
  80           /* Remove trailing newline.  rnd_base64 had better be
  81              shorter than 76 characters, so don't bother to look for
  82              embedded newlines. */
  83           rnd_base64[i] = '\0';
  84         }
  85
  86         /* Try to make the base64 string look a little more like a
  87            hostname by replacing + with - and / with _. */
  88         for (cp = rnd_base64; *cp; ++cp) {
  89           if (*cp == '+') {
  90             *cp = '-';
  91           } else if (*cp == '/') {
  92             *cp = '_';
  93           }
  94         }
  95
  96         /* gettimeofday() and getpid() shouldn't fail on POSIX platforms. */
  97         gettimeofday (&now, 0);
  98
  99         /* The format string inserts a couple of dots, for the benefit
 100            of spam filters that want to see a message id with a final
 101            part that resembles a hostname. */
 102 #define P(fmt) \
 103     snprintf(message_id_, sizeof message_id_, (fmt), \
 104         getpid(), (long)now.tv_sec, (long)now.tv_usec, \
 105         (int)one_third, rnd_base64, \
 106         (int)one_third, &rnd_base64[one_third], \
 107         (int)one_third, &rnd_base64[2*one_third])
 108
 109             if (content_id)
 110                 P("<%d-%ld.%06ld%%d@%.*s.%.*s.%.*s>");
 111             else
 112                 P("<%d-%ld.%06ld@%.*s.%.*s.%.*s>");
 113 #undef P
 114       }
 115
 116       break;
 117     }
 118   }
 119
 120   return message_id_;
 121 }