Fix our compliance with RFC 3261 section 18.2.2.

This change optimizes the free_via() function and removes some redundant null
checking. It also fixes compliance with RFC 3261 section 18.2.2 by always using
the port specified in the Via header for routing responses (even when maddr is
not set). Also the htons() function is now used when setting the port.
Additional documentation comments have been added in various places to make the
logic in the code clearer.

(closes issue #18951)
Reported by: jmls
Patches:
      issue18951_set_proper_port_from_via.patch uploaded by wdoekes (license 717) (modified)


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@315891 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -4973,10 +4973,7 @@ static void free_via(struct sip_via *v)
 		return;
 	}
 
-	if (v->via) {
-		ast_free(v->via);
-	}
-
+	ast_free(v->via);
 	ast_free(v);
 }
 
@@ -5099,6 +5096,21 @@ static int addr_is_multicast(struct in_addr *addr)
 	return ((ntohl(addr->s_addr) & 0xf0000000) == 0xe0000000);
 }
 
+/*!
+ * \brief Process the Via header according to RFC 3261 section 18.2.2.
+ * \param p a sip_pvt structure that will be modified according to the received
+ * header
+ * \param req a sip request with a Via header to process
+ *
+ * This function will update the destination of the response according to the
+ * Via header in the request and RFC 3261 section 18.2.2. We do not have a
+ * transport layer so we ignore certain values like the 'received' param (we
+ * set the destination address to the addres the request came from in the
+ * respprep() function).
+ *
+ * \retval -1 error
+ * \retval 0 success
+ */
 static int process_via(struct sip_pvt *p, const struct sip_request *req)
 {
 	struct sip_via *via = parse_via(get_header(req, "Via"));
@@ -5123,17 +5135,13 @@ static int process_via(struct sip_pvt *p, const struct sip_request *req)
 		p->sa.sin_family = AF_INET;
 		memcpy(&p->sa.sin_addr, hp->h_addr, sizeof(p->sa.sin_addr));
 
-		if (via->port) {
-			p->sa.sin_port = via->port;
-		} else {
-			p->sa.sin_port = STANDARD_SIP_PORT;
-		}
-
 		if (addr_is_multicast(&p->sa.sin_addr)) {
 			setsockopt(sipsock, IPPROTO_IP, IP_MULTICAST_TTL, &via->ttl, sizeof(via->ttl));
 		}
 	}
 
+	p->sa.sin_port = htons(via->port ? via->port : STANDARD_SIP_PORT);
+
 	free_via(via);
 	return 0;
 }
@@ -6785,6 +6793,9 @@ static int respprep(struct sip_request *resp, struct sip_pvt *p, const char *msg
 
 	/* default to routing the response to the address where the request
 	 * came from.  Since we don't have a transport layer, we do this here.
+	 * The process_via() function will update the port to either the port
+	 * specified in the via header or the default port later on (per RFC
+	 * 3261 section 18.2.2).
 	 */
 	p->sa = p->recv;