Allow for UDPTL to use only even-numbered ports if desired.

There are some VoIP providers out there that will not accept SDP
offers with odd numbered UDPTL ports. While it is my personal opinion
that these VoIP providers are misinterpreting RFC 2327, it really is
not a big deal to play along with their silly little games. Of course,
since restricting UDPTL ports to only even numbers reduces the range
of available ports by half, so the option to use only even port numbers
is off by default. A user can enable the behavior by setting
use_even_ports=yes in udptl.conf.

(closes issue #15182)
Reported by: CGMChris
Patches:
      15182.patch uploaded by mmichelson (license 60)
Tested by: CGMChris



git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@209131 65c4cc65-6c06-0410-ace0-fbb531ad65f3

configs/udptl.conf.sample

@@ -28,3 +28,8 @@ udptlfecentries = 3
 ; The span over which parity is calculated for FEC in a UDPTL packet
 ;
 udptlfecspan = 3
+;
+; Some VoIP providers will only accept an offer with an even-numbered
+; UDPTL port. Set this option so that Asterisk will only attempt to use
+; even-numbered ports when negotiating T.38. Default is no.
+use_even_ports = no

main/udptl.c

@@ -66,6 +66,7 @@ static int udptlfectype;
 static int udptlfecentries;
 static int udptlfecspan;
 static int udptlmaxdatagram;
+static int use_even_ports;
 
 #define LOCAL_FAX_MAX_DATAGRAM      1400
 #define MAX_FEC_ENTRIES             5
@@ -795,6 +796,9 @@ struct ast_udptl *ast_udptl_new_with_bindaddr(struct sched_context *sched, struc
 #endif
 	/* Find us a place */
 	x = (ast_random() % (udptlend - udptlstart)) + udptlstart;
+	if (use_even_ports && (x & 1)) {
+		++x;
+	}
 	startplace = x;
 	for (;;) {
 		udptl->us.sin_port = htons(x);
@@ -807,7 +811,12 @@ struct ast_udptl *ast_udptl_new_with_bindaddr(struct sched_context *sched, struc
 			free(udptl);
 			return NULL;
 		}
-		if (++x > udptlend)
+		if (use_even_ports) {
+			x += 2;
+		} else {
+			++x;
+		}
+		if (x > udptlend)
 			x = udptlstart;
 		if (x == startplace) {
 			ast_log(LOG_WARNING, "No UDPTL ports remaining\n");
@@ -1183,6 +1192,7 @@ void ast_udptl_reload(void)
 	udptlfecentries = 0;
 	udptlfecspan = 0;
 	udptlmaxdatagram = 0;
+	use_even_ports = 0;
 
 	if ((cfg = ast_config_load("udptl.conf"))) {
 		if ((s = ast_variable_retrieve(cfg, "general", "udptlstart"))) {
@@ -1257,6 +1267,9 @@ void ast_udptl_reload(void)
 				udptlfecspan = MAX_FEC_SPAN;
 			}
 		}
+		if ((s = ast_variable_retrieve(cfg, "general", "use_even_ports"))) {
+			use_even_ports = ast_true(s);
+		}
 		ast_config_destroy(cfg);
 	}
 	if (udptlstart >= udptlend) {
@@ -1264,6 +1277,14 @@ void ast_udptl_reload(void)
 		udptlstart = 4500;
 		udptlend = 4999;
 	}
+	if (use_even_ports && (udptlstart & 1)) {
+		++udptlstart;
+		ast_log(LOG_NOTICE, "Odd numbered udptlstart specified but use_even_ports enabled. udptlstart is now %d\n", udptlstart);
+	}
+	if (use_even_ports && (udptlend & 1)) {
+		--udptlend;
+		ast_log(LOG_NOTICE, "Odd numbered udptlend specified but use_event_ports enabled. udptlend is now %d\n", udptlend);
+	}
 	if (option_verbose > 1)
 		ast_verbose(VERBOSE_PREFIX_2 "UDPTL allocating from port range %d -> %d\n", udptlstart, udptlend);
 }