chan_pjsip: fix switching sending codec when asymmetric_rtp_codec=no

The sending codec is switched to the receiving codec and then
is switched back to the best native codec on EVERY receiving RTP packets.
This is because after call of ast_channel_set_rawwriteformat there is call
of ast_set_write_format which calls set_format which sets rawwriteformat
to the best native format.

This patch adds a new function ast_set_write_format_path which set
specific write path on channel and uses this function to switch
the sending codec.

ASTERISK-26603 #close

Change-Id: I5b7d098f8b254ce8f45546e6c36e5d324737f71d

channels/chan_pjsip.c

@@ -677,7 +677,11 @@ static struct ast_frame *chan_pjsip_cng_tone_detected(struct ast_sip_session *se
 	return f;
 }
 
-/*! \brief Function called by core to read any waiting frames */
+/*!
+ * \brief Function called by core to read any waiting frames 
+ *
+ * \note The channel is already locked.
+ */
 static struct ast_frame *chan_pjsip_read(struct ast_channel *ast)
 {
 	struct ast_sip_channel_pvt *channel = ast_channel_tech_pvt(ast);
@@ -735,8 +739,7 @@ static struct ast_frame *chan_pjsip_read(struct ast_channel *ast)
 		ast_debug(1, "Oooh, got a frame with format of %s on channel '%s' when we're sending '%s', switching to match\n",
 			ast_format_get_name(f->subclass.format), ast_channel_name(ast),
 			ast_format_get_name(ast_channel_rawwriteformat(ast)));
-		ast_channel_set_rawwriteformat(ast, f->subclass.format);
-		ast_set_write_format(ast, ast_channel_writeformat(ast));
+		ast_set_write_format_path(ast, ast_channel_writeformat(ast), f->subclass.format);
 
 		if (ast_channel_is_bridged(ast)) {
 			ast_channel_set_unbridged_nolock(ast, 1);

include/asterisk/channel.h

@@ -1992,6 +1992,21 @@ int ast_prod(struct ast_channel *chan);
  */
 int ast_set_read_format_path(struct ast_channel *chan, struct ast_format *raw_format, struct ast_format *core_format);
 
+/*!
+ * \brief Set specific write path on channel.
+ * \since 13.13.0
+ *
+ * \param chan Channel to setup write path.
+ * \param core_format What the core wants to write.
+ * \param raw_format Raw write format.
+ *
+ * \pre chan is locked
+ *
+ * \retval 0 on success.
+ * \retval -1 on error.
+ */
+int ast_set_write_format_path(struct ast_channel *chan, struct ast_format *core_format, struct ast_format *raw_format);
+
 /*!
  * \brief Sets read format on channel chan from capabilities
  * Set read format for channel to whichever component of "format" is best.

main/channel.c

@@ -5474,6 +5474,42 @@ int ast_set_read_format_path(struct ast_channel *chan, struct ast_format *raw_fo
 	return 0;
 }
 
+int ast_set_write_format_path(struct ast_channel *chan, struct ast_format *core_format, struct ast_format *raw_format)
+{
+	struct ast_trans_pvt *trans_old;
+	struct ast_trans_pvt *trans_new;
+
+	if (ast_format_cmp(ast_channel_rawwriteformat(chan), raw_format) == AST_FORMAT_CMP_EQUAL
+		&& ast_format_cmp(ast_channel_writeformat(chan), core_format) == AST_FORMAT_CMP_EQUAL) {
+		/* Nothing to setup */
+		return 0;
+	}
+
+	ast_debug(1, "Channel %s setting write format path: %s -> %s\n",
+		ast_channel_name(chan),
+		ast_format_get_name(core_format),
+		ast_format_get_name(raw_format));
+
+	/* Setup new translation path. */
+	if (ast_format_cmp(raw_format, core_format) != AST_FORMAT_CMP_EQUAL) {
+		trans_new = ast_translator_build_path(raw_format, core_format);
+		if (!trans_new) {
+			return -1;
+		}
+	} else {
+		/* No translation needed. */
+		trans_new = NULL;
+	}
+	trans_old = ast_channel_writetrans(chan);
+	if (trans_old) {
+		ast_translator_free_path(trans_old);
+	}
+	ast_channel_writetrans_set(chan, trans_new);
+	ast_channel_set_rawwriteformat(chan, raw_format);
+	ast_channel_set_writeformat(chan, core_format);
+	return 0;
+}
+
 struct set_format_access {
 	const char *direction;
 	struct ast_trans_pvt *(*get_trans)(const struct ast_channel *chan);