/*++ /* NAME /* mail_flow 3 /* SUMMARY /* global mail flow control /* SYNOPSIS /* #include <mail_flow.h> /* /* ssize_t mail_flow_get(count) /* ssize_t count; /* /* ssize_t mail_flow_put(count) /* ssize_t count; /* /* ssize_t mail_flow_count() /* DESCRIPTION /* This module implements a simple flow control mechanism that /* is based on tokens that are consumed by mail receiving processes /* and that are produced by mail sending processes. /* /* mail_flow_get() attempts to read specified number of tokens. The /* result is > 0 for success, < 0 for failure. In the latter case, /* the process is expected to slow down a little. /* /* mail_flow_put() produces the specified number of tokens. The /* token producing process is expected to produce new tokens /* whenever it falls idle and no more tokens are available. /* /* mail_flow_count() returns the number of available tokens. /* BUGS /* The producer needs to wake up periodically to ensure that /* tokens are not lost due to leakage. /* LICENSE /* .ad /* .fi /* The Secure Mailer license must be distributed with this software. /* AUTHOR(S) /* Wietse Venema /* IBM T.J. Watson Research /* P.O. Box 704 /* Yorktown Heights, NY 10598, USA /*--*/ /* System library. */ #include <sys_defs.h> #include <sys/stat.h> #include <unistd.h> #include <stdlib.h> #include <string.h> /* Utility library. */ #include <msg.h> #include <iostuff.h> #include <warn_stat.h> /* Global library. */ #include <mail_flow.h> /* Master library. */ #include <master_proto.h> #define BUFFER_SIZE 1024 /* mail_flow_get - read N tokens */ ssize_t mail_flow_get(ssize_t len) { const char *myname = "mail_flow_get"; char buf[BUFFER_SIZE]; struct stat st; ssize_t count; ssize_t n = 0; /* * Sanity check. */ if (len <= 0) msg_panic("%s: bad length %ld", myname, (long) len); /* * Silence some wild claims. */ if (fstat(MASTER_FLOW_WRITE, &st) < 0) msg_fatal("fstat flow pipe write descriptor: %m"); /* * Read and discard N bytes. XXX AIX read() can return 0 when an open * pipe is empty. */ for (count = len; count > 0; count -= n) if ((n = read(MASTER_FLOW_READ, buf, count > BUFFER_SIZE ? BUFFER_SIZE : count)) <= 0) return (-1); if (msg_verbose) msg_info("%s: %ld %ld", myname, (long) len, (long) (len - count)); return (len - count); } /* mail_flow_put - put N tokens */ ssize_t mail_flow_put(ssize_t len) { const char *myname = "mail_flow_put"; char buf[BUFFER_SIZE]; ssize_t count; ssize_t n = 0; /* * Sanity check. */ if (len <= 0) msg_panic("%s: bad length %ld", myname, (long) len); /* * Write or discard N bytes. */ memset(buf, 0, len > BUFFER_SIZE ? BUFFER_SIZE : len); for (count = len; count > 0; count -= n) if ((n = write(MASTER_FLOW_WRITE, buf, count > BUFFER_SIZE ? BUFFER_SIZE : count)) < 0) return (-1); if (msg_verbose) msg_info("%s: %ld %ld", myname, (long) len, (long) (len - count)); return (len - count); } /* mail_flow_count - return number of available tokens */ ssize_t mail_flow_count(void) { const char *myname = "mail_flow_count"; ssize_t count; if ((count = peekfd(MASTER_FLOW_READ)) < 0) msg_warn("%s: %m", myname); return (count); }