external/ibm-public/postfix/dist/src/master/mail_flow.c

   1 /*      $NetBSD$        */
   2
   3 /*++
   4 /* NAME
   5 /*      mail_flow 3
   6 /* SUMMARY
   7 /*      global mail flow control
   8 /* SYNOPSIS
   9 /*      #include <mail_flow.h>
  10 /*
  11 /*      ssize_t mail_flow_get(count)
  12 /*      ssize_t count;
  13 /*
  14 /*      ssize_t mail_flow_put(count)
  15 /*      ssize_t count;
  16 /*
  17 /*      ssize_t mail_flow_count()
  18 /* DESCRIPTION
  19 /*      This module implements a simple flow control mechanism that
  20 /*      is based on tokens that are consumed by mail receiving processes
  21 /*      and that are produced by mail sending processes.
  22 /*
  23 /*      mail_flow_get() attempts to read specified number of tokens. The
  24 /*      result is > 0 for success, < 0 for failure. In the latter case,
  25 /*      the process is expected to slow down a little.
  26 /*
  27 /*      mail_flow_put() produces the specified number of tokens. The
  28 /*      token producing process is expected to produce new tokens
  29 /*      whenever it falls idle and no more tokens are available.
  30 /*
  31 /*      mail_flow_count() returns the number of available tokens.
  32 /* BUGS
  33 /*      The producer needs to wake up periodically to ensure that
  34 /*      tokens are not lost due to leakage.
  35 /* LICENSE
  36 /* .ad
  37 /* .fi
  38 /*      The Secure Mailer license must be distributed with this software.
  39 /* AUTHOR(S)
  40 /*      Wietse Venema
  41 /*      IBM T.J. Watson Research
  42 /*      P.O. Box 704
  43 /*      Yorktown Heights, NY 10598, USA
  44 /*--*/
  45
  46 /* System library. */
  47
  48 #include <sys_defs.h>
  49 #include <sys/stat.h>
  50 #include <unistd.h>
  51 #include <stdlib.h>
  52 #include <string.h>
  53
  54 /* Utility library. */
  55
  56 #include <msg.h>
  57 #include <iostuff.h>
  58
  59 /* Global library. */
  60
  61 #include <mail_flow.h>
  62
  63 /* Master library. */
  64
  65 #include <master_proto.h>
  66
  67 #define BUFFER_SIZE     1024
  68
  69 /* mail_flow_get - read N tokens */
  70
  71 ssize_t mail_flow_get(ssize_t len)
  72 {
  73     const char *myname = "mail_flow_get";
  74     char    buf[BUFFER_SIZE];
  75     struct stat st;
  76     ssize_t count;
  77     ssize_t n = 0;
  78
  79     /*
  80      * Sanity check.
  81      */
  82     if (len <= 0)
  83         msg_panic("%s: bad length %ld", myname, (long) len);
  84
  85     /*
  86      * Silence some wild claims.
  87      */
  88     if (fstat(MASTER_FLOW_WRITE, &st) < 0)
  89         msg_fatal("fstat flow pipe write descriptor: %m");
  90
  91     /*
  92      * Read and discard N bytes. XXX AIX read() can return 0 when an open
  93      * pipe is empty.
  94      */
  95     for (count = len; count > 0; count -= n)
  96         if ((n = read(MASTER_FLOW_READ, buf, count > BUFFER_SIZE ?
  97                       BUFFER_SIZE : count)) <= 0)
  98             return (-1);
  99     if (msg_verbose)
 100         msg_info("%s: %ld %ld", myname, (long) len, (long) (len - count));
 101     return (len - count);
 102 }
 103
 104 /* mail_flow_put - put N tokens */
 105
 106 ssize_t mail_flow_put(ssize_t len)
 107 {
 108     const char *myname = "mail_flow_put";
 109     char    buf[BUFFER_SIZE];
 110     ssize_t count;
 111     ssize_t n = 0;
 112
 113     /*
 114      * Sanity check.
 115      */
 116     if (len <= 0)
 117         msg_panic("%s: bad length %ld", myname, (long) len);
 118
 119     /*
 120      * Write or discard N bytes.
 121      */
 122     memset(buf, 0, len > BUFFER_SIZE ? BUFFER_SIZE : len);
 123
 124     for (count = len; count > 0; count -= n)
 125         if ((n = write(MASTER_FLOW_WRITE, buf, count > BUFFER_SIZE ?
 126                        BUFFER_SIZE : count)) < 0)
 127             return (-1);
 128     if (msg_verbose)
 129         msg_info("%s: %ld %ld", myname, (long) len, (long) (len - count));
 130     return (len - count);
 131 }
 132
 133 /* mail_flow_count - return number of available tokens */
 134
 135 ssize_t mail_flow_count(void)
 136 {
 137     const char *myname = "mail_flow_count";
 138     ssize_t count;
 139
 140     if ((count = peekfd(MASTER_FLOW_READ)) < 0)
 141         msg_warn("%s: %m", myname);
 142     return (count);
 143 }