sendmail: make it possible to pause after connection helper is started

If a non-starttls helper is in use, initial 220 response is processed by us,
not by helper.
Some servers consider us to be a spammer if we don't wait for it.

It is not in protocol, but it is a real-life problem.

The workaround in this patch is a magic envvar, $SMTP_ANTISPAM_DELAY:

...
	-H 'PROG ARGS'	Run connection helper. Examples:
		openssl s_client -quiet -tls1 -starttls smtp -connect smtp.gmail.com:25
		openssl s_client -quiet -tls1 -connect smtp.gmail.com:465
			$SMTP_ANTISPAM_DELAY: seconds to wait after helper connect
...

By using it, people can tweak sendmail behavior even if sendmail invocation
is buried in some scripts.

function                                             old     new   delta
packed_usage                                       30464   30497     +33
sendmail_main                                       1185    1206     +21
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/0 up/down: 54/0)               Total: 54 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 14 insertions, 10 deletions

diff --git a/mailutils/sendmail.c b/mailutils/sendmail.c
index cd27d676e..1242795b8 100644
--- a/mailutils/sendmail.c
+++ b/mailutils/sendmail.c
@@ -27,6 +27,7 @@
 //usage:     "\n        -H 'PROG ARGS'  Run connection helper. Examples:"
 //usage:     "\n                openssl s_client -quiet -tls1 -starttls smtp -connect smtp.gmail.com:25"
 //usage:     "\n                openssl s_client -quiet -tls1 -connect smtp.gmail.com:465"
+//usage:     "\n                        $SMTP_ANTISPAM_DELAY: seconds to wait after helper connect"
 //usage:     "\n        -S HOST[:PORT]  Server (default $SMTPHOST or 127.0.0.1)"
 //usage:     "\n        -amLOGIN        Log in using AUTH LOGIN (-amCRAM-MD5 not supported)"
 //usage:     "\n        -auUSER         Username for AUTH"
@@ -207,7 +208,7 @@ static void rcptto_list(const char *list)
 int sendmail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int sendmail_main(int argc UNUSED_PARAM, char **argv)
 {
-        char *opt_connect = opt_connect;
+        char *opt_connect;
         char *opt_from = NULL;
         char *s;
         llist_t *list = NULL;
@@ -239,6 +240,11 @@ int sendmail_main(int argc UNUSED_PARAM, char **argv)
         // init global variables
         INIT_G();
 
+        // default HOST[:PORT] is $SMTPHOST, or localhost
+        opt_connect = getenv("SMTPHOST");
+        if (!opt_connect)
+                opt_connect = (char *)"127.0.0.1";
+
         // save initial stdin since body is piped!
         xdup2(STDIN_FILENO, 3);
         G.fp0 = xfdopen_for_read(3);
@@ -274,6 +280,7 @@ int sendmail_main(int argc UNUSED_PARAM, char **argv)
 
         // connection helper ordered? ->
         if (opts & OPT_H) {
+                const char *delay;
                 const char *args[] = { "sh", "-c", opt_connect, NULL };
                 // plug it in
                 launch_helper(args);
@@ -292,7 +299,12 @@ int sendmail_main(int argc UNUSED_PARAM, char **argv)
                 // before 220 reached it. The code below is unsafe in this regard:
                 // in non-STARTTLSed case, we potentially send NOOP before 220
                 // is sent by server.
-                // Ideas? (--delay SECS opt? --assume-starttls-helper opt?)
+                //
+                // If $SMTP_ANTISPAM_DELAY is set, we pause before sending NOOP.
+                //
+                delay = getenv("SMTP_ANTISPAM_DELAY");
+                if (delay)
+                        sleep(atoi(delay));
                 code = smtp_check("NOOP", -1);
                 if (code == 220)
                         // we got 220 - this is not STARTTLSed connection,
@@ -304,14 +316,6 @@ int sendmail_main(int argc UNUSED_PARAM, char **argv)
         } else {
                 // vanilla connection
                 int fd;
-                // host[:port] not explicitly specified? -> use $SMTPHOST
-                // no $SMTPHOST? -> use localhost
-                if (!(opts & OPT_S)) {
-                        opt_connect = getenv("SMTPHOST");
-                        if (!opt_connect)
-                                opt_connect = (char *)"127.0.0.1";
-                }
-                // do connect
                 fd = create_and_connect_stream_or_die(opt_connect, 25);
                 // and make ourselves a simple IO filter
                 xmove_fd(fd, STDIN_FILENO);