From e3a5c463b5c479f60f83376c7d3b4bce74914b13 Mon Sep 17 00:00:00 2001
From: Justine Alexandra Roberts Tunney <jtunney@gmail.com>
Date: Sun, 28 Dec 2014 06:46:08 -0500
Subject: [PATCH] Cleaner RTP channels.

---
 rtp/session.go  | 61 ++++++++++++++++++++-----------------------------
 sip/receiver.go |  2 +-
 2 files changed, 26 insertions(+), 37 deletions(-)

diff --git a/rtp/session.go b/rtp/session.go
index fce53e4..c35e97c 100644
--- a/rtp/session.go
+++ b/rtp/session.go
@@ -3,8 +3,6 @@
 package rtp
 
 import (
-	"errors"
-	"fmt"
 	"github.com/jart/gosip/dsp"
 	"github.com/jart/gosip/sdp"
 	"log"
@@ -28,8 +26,8 @@ type Frame [160]int16
 type Session struct {
 
 	// Channel to which received RTP frames and errors are published.
-	C chan *Frame
-	E chan error
+	C <-chan *Frame
+	E <-chan error
 
 	// Underlying UDP socket.
 	Sock *net.UDPConn
@@ -41,21 +39,24 @@ type Session struct {
 	// Header is the current header that gets mutated with each transmit.
 	Header Header
 
-	ibuf []byte
 	obuf []byte
 }
 
 // Creates a new RTP µLaw 20ptime session listening on host with a random port
 // selected from the range [16384,32768].
 func NewSession(host string) (rs *Session, err error) {
-	sock, err := listenRTP(host)
+	conn, err := listenRTP(host)
 	if err != nil {
 		return nil, err
 	}
-	rs = &Session{
-		C:    make(chan *Frame, 4),
-		E:    make(chan error, 1),
-		Sock: sock.(*net.UDPConn),
+	sock := conn.(*net.UDPConn)
+	c := make(chan *Frame, 4)
+	e := make(chan error, 1)
+	go receiver(sock, c, e)
+	return &Session{
+		C:    c,
+		E:    e,
+		Sock: sock,
 		Header: Header{
 			PT:   sdp.ULAWCodec.PT,
 			Seq:  666,
@@ -63,10 +64,7 @@ func NewSession(host string) (rs *Session, err error) {
 			Ssrc: rand.Uint32(),
 		},
 		obuf: make([]byte, HeaderSize+160),
-		ibuf: make([]byte, 2048),
-	}
-	rs.launchConsumer()
-	return
+	}, nil
 }
 
 func (rs *Session) Send(frame *Frame) (err error) {
@@ -83,45 +81,36 @@ func (rs *Session) Send(frame *Frame) (err error) {
 	return
 }
 
-func (rs *Session) launchConsumer() {
-	go func() {
-		for {
-			frame, err := rs.recv()
-			if err != nil {
-				rs.E <- err
-				return
-			}
-			rs.C <- frame
-		}
-	}()
-}
-
-func (rs *Session) recv() (frame *Frame, err error) {
-	frame = new(Frame)
+func receiver(sock *net.UDPConn, c chan<- *Frame, e chan<- error) {
+	buf := make([]byte, 2048)
+	frame := new(Frame)
 	for {
-		amt, _, err := rs.Sock.ReadFrom(rs.ibuf)
+		amt, _, err := sock.ReadFrom(buf)
 		if err != nil {
-			return nil, err
+			e <- err
+			break
 		}
 		// TODO(jart): Verify source address?
 		// TODO(jart): Packet reordering? Drop duplicate packets?
 		// TODO(jart): DTMF?
 		var phdr Header
-		err = phdr.Read(rs.ibuf)
+		err = phdr.Read(buf)
 		if err != nil {
-			return nil, err
+			// TODO(jart): Best logging strategy?
+			continue
 		}
 		if phdr.PT != sdp.ULAWCodec.PT {
 			continue
 		}
 		if amt != HeaderSize+160 {
-			return nil, errors.New(fmt.Sprintf("Unexpected RTP packet size: %d", amt))
+			continue
 		}
 		for n := 0; n < 160; n++ {
-			frame[n] = int16(dsp.UlawToLinear(int64(rs.ibuf[HeaderSize+n])))
+			frame[n] = int16(dsp.UlawToLinear(int64(buf[HeaderSize+n])))
 		}
-		return frame, nil
+		c <- frame
 	}
+	close(c)
 }
 
 func listenRTP(host string) (sock net.PacketConn, err error) {
diff --git a/sip/receiver.go b/sip/receiver.go
index 5d766e7..a6a17d1 100644
--- a/sip/receiver.go
+++ b/sip/receiver.go
@@ -34,7 +34,7 @@ func ReceiveMessages(contact *Addr, sock *net.UDPConn, c chan<- *Msg, e chan<- e
 		c <- msg
 	}
 	close(c)
-	close(e)
+	close(e) // Must be unbuffered!
 }
 
 func addReceived(msg *Msg, addr *net.UDPAddr) {