From c5ddec43f0f12e48979f1a4c2bc3a03ca683a45d Mon Sep 17 00:00:00 2001
From: Denys Smirnov <dennwc@pm.me>
Date: Fri, 22 Dec 2023 20:12:14 +0200
Subject: [PATCH] Set media destination from SDP. (#36)

---
 pkg/sip/inbound.go   | 11 +++++++----
 pkg/sip/signaling.go | 26 ++++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/pkg/sip/inbound.go b/pkg/sip/inbound.go
index 759a212b..948da57a 100644
--- a/pkg/sip/inbound.go
+++ b/pkg/sip/inbound.go
@@ -256,16 +256,19 @@ func (c *inboundCall) sendBye() {
 }
 
 func (c *inboundCall) runMediaConn(offerData []byte, conf *config.Config) (answerData []byte, _ error) {
+	offer := sdp.SessionDescription{}
+	if err := offer.Unmarshal(offerData); err != nil {
+		return nil, err
+	}
 	conn := NewMediaConn()
 	conn.OnRTP(c)
+	if dst := sdpGetAudioDest(offer); dst != nil {
+		conn.SetDestAddr(dst)
+	}
 	if err := conn.Start(conf.RTPPort.Start, conf.RTPPort.End, "0.0.0.0"); err != nil {
 		return nil, err
 	}
 	c.rtpConn = conn
-	offer := sdp.SessionDescription{}
-	if err := offer.Unmarshal(offerData); err != nil {
-		return nil, err
-	}
 
 	// Encoding pipeline (LK -> SIP)
 	// Need to be created earlier to send the pin prompts.
diff --git a/pkg/sip/signaling.go b/pkg/sip/signaling.go
index 30fd81d0..36a235c9 100644
--- a/pkg/sip/signaling.go
+++ b/pkg/sip/signaling.go
@@ -16,6 +16,8 @@ package sip
 
 import (
 	"math/rand"
+	"net"
+	"net/netip"
 
 	"github.com/pion/sdp/v2"
 )
@@ -108,3 +110,27 @@ func sdpGenerateAnswer(offer sdp.SessionDescription, publicIp string, rtpListene
 
 	return answer.Marshal()
 }
+
+func sdpGetAudioDest(offer sdp.SessionDescription) *net.UDPAddr {
+	ci := offer.ConnectionInformation
+	if ci.NetworkType != "IN" {
+		return nil
+	}
+	ip, err := netip.ParseAddr(ci.Address.Address)
+	if err != nil {
+		return nil
+	}
+	var audio *sdp.MediaDescription
+	for _, m := range offer.MediaDescriptions {
+		if m.MediaName.Media == "audio" {
+			audio = m
+		}
+	}
+	if audio == nil {
+		return nil
+	}
+	return &net.UDPAddr{
+		IP:   ip.AsSlice(),
+		Port: audio.MediaName.Port.Value,
+	}
+}