res_fax/t38_gateway: Peer V.21 session is created on wrong channel

The channel and peer V.21 sessions are created on the same channel now.
The peer V.21 session should be created only on peer channel
when one of channel can handle T.38.

Also this patch enable debug for T.38 gateway session
if global fax debug enabled.

ASTERISK-25982

Change-Id: I78387156ea521a77eb0faf170179ddd37a50430e

res/res_fax.c

@@ -626,6 +626,8 @@ static const struct ast_datastore_info fax_datastore = {
 static int fax_gateway_attach(struct ast_channel *chan, struct ast_fax_session_details *details);
 static int fax_detect_attach(struct ast_channel *chan, int timeout, int flags);
 static struct ast_fax_session_details *find_or_create_details(struct ast_channel *chan);
+static struct ast_fax_session *fax_v21_session_new (struct ast_channel *chan);
+
 
 /*! \brief Copies fax detection and gateway framehooks during masquerades
  *
@@ -2827,6 +2829,23 @@ static void destroy_gateway(void *data)
 	ao2_cleanup(gateway->peer_write_format);
 }
 
+static struct ast_fax_session *fax_v21_session_new (struct ast_channel *chan) {
+	struct ast_fax_session_details *v21_details;
+	struct ast_fax_session *v21_session;
+
+	if (!chan || !(v21_details = session_details_new())) {
+		return NULL;
+	}
+
+	v21_details->caps = AST_FAX_TECH_V21_DETECT;
+	if (!(v21_session = fax_session_new(v21_details, chan, NULL, NULL))) {
+		ao2_ref(v21_details, -1);
+		return NULL;
+	}
+
+	return v21_session;
+}
+
 /*! \brief Create a new fax gateway object.
  * \param chan the channel the gateway object will be attached to
  * \param details the fax session details
@@ -2835,29 +2854,15 @@ static void destroy_gateway(void *data)
 static struct fax_gateway *fax_gateway_new(struct ast_channel *chan, struct ast_fax_session_details *details)
 {
 	struct fax_gateway *gateway = ao2_alloc(sizeof(*gateway), destroy_gateway);
-	struct ast_fax_session_details *v21_details;
 	if (!gateway) {
 		return NULL;
 	}
 
-	if (!(v21_details = session_details_new())) {
-		ao2_ref(gateway, -1);
-		return NULL;
-	}
-
-	v21_details->caps = AST_FAX_TECH_V21_DETECT;
-	if (!(gateway->chan_v21_session = fax_session_new(v21_details, chan, NULL, NULL))) {
-		ao2_ref(v21_details, -1);
-		ao2_ref(gateway, -1);
-		return NULL;
-	}
-
-	if (!(gateway->peer_v21_session = fax_session_new(v21_details, chan, NULL, NULL))) {
-		ao2_ref(v21_details, -1);
+	if (!(gateway->chan_v21_session = fax_v21_session_new(chan))) {
+		ast_log(LOG_ERROR, "Can't create V21 session on chan %s for T.38 gateway session\n", ast_channel_name(chan));
 		ao2_ref(gateway, -1);
 		return NULL;
 	}
-	ao2_ref(v21_details, -1);
 
 	gateway->framehook = -1;
 
@@ -3352,6 +3357,11 @@ static struct ast_frame *fax_gateway_framehook(struct ast_channel *chan, struct
 		ast_channel_unlock(peer);
 
 		gateway->bridged = 1;
+		if (!(gateway->peer_v21_session = fax_v21_session_new(peer))) {
+			ast_log(LOG_ERROR, "Can't create V21 session on chan %s for T.38 gateway session\n", ast_channel_name(peer));
+			ast_framehook_detach(chan, gateway->framehook);
+			return f;
+		}
 	}
 
 	if (gateway->bridged && !ast_tvzero(gateway->timeout_start)) {
@@ -3478,6 +3488,10 @@ static int fax_gateway_attach(struct ast_channel *chan, struct ast_fax_session_d
 		.disable_inheritance = 1, /* Masquerade inheritance is handled through the datastore fixup */
 	};
 
+    	if (global_fax_debug) {
+        	details->option.debug = AST_FAX_OPTFLAG_TRUE;
+    	}
+
 	ast_string_field_set(details, result, "SUCCESS");
 	ast_string_field_set(details, resultstr, "gateway operation started successfully");
 	ast_string_field_set(details, error, "NO_ERROR");