Optimise mux.dispatch

Uncurry the function MuxRange and avoid allocating a reader in
isRTCP.  The included benchmark indicates that we avoid five
allocations per packet.

Author: jech

internal/mux/mux_test.go

@@ -142,3 +142,29 @@ func TestNonFatalRead(t *testing.T) {
 	assert.NoError(t, m.Close())
 	assert.NoError(t, ca.Close())
 }
+
+func BenchmarkDispatch(b *testing.B) {
+	m := &Mux{
+		endpoints: make(map[*Endpoint]MatchFunc),
+		log:       logging.NewDefaultLoggerFactory().NewLogger("mux"),
+	}
+
+	e := m.NewEndpoint(MatchSRTP)
+	m.NewEndpoint(MatchSRTCP)
+
+	buf := []byte{128, 1, 2, 3, 4}
+	buf2 := make([]byte, 1200)
+
+	b.StartTimer()
+
+	for i := 0; i < b.N; i++ {
+		err := m.dispatch(buf)
+		if err != nil {
+			b.Errorf("dispatch: %v", err)
+		}
+		_, err = e.buffer.Read(buf2)
+		if err != nil {
+			b.Errorf("read: %v", err)
+		}
+	}
+}

internal/mux/muxfunc.go

@@ -1,10 +1,5 @@
 package mux
 
-import (
-	"bytes"
-	"encoding/binary"
-)
-
 // MatchFunc allows custom logic for mapping packets to an Endpoint
 type MatchFunc func([]byte) bool
 
@@ -13,15 +8,13 @@ func MatchAll(b []byte) bool {
 	return true
 }
 
-// MatchRange is a MatchFunc that accepts packets with the first byte in [lower..upper]
-func MatchRange(lower, upper byte) MatchFunc {
-	return func(buf []byte) bool {
-		if len(buf) < 1 {
-			return false
-		}
-		b := buf[0]
-		return b >= lower && b <= upper
+// MatchRange returns true if the first byte of buf is in [lower..upper]
+func MatchRange(lower, upper byte, buf []byte) bool {
+	if len(buf) < 1 {
+		return false
 	}
+	b := buf[0]
+	return b >= lower && b <= upper
 }
 
 // MatchFuncs as described in RFC7983
@@ -41,30 +34,21 @@ func MatchRange(lower, upper byte) MatchFunc {
 // MatchDTLS is a MatchFunc that accepts packets with the first byte in [20..63]
 // as defied in RFC7983
 func MatchDTLS(b []byte) bool {
-	return MatchRange(20, 63)(b)
+	return MatchRange(20, 63, b)
 }
 
 // MatchSRTPOrSRTCP is a MatchFunc that accepts packets with the first byte in [128..191]
 // as defied in RFC7983
 func MatchSRTPOrSRTCP(b []byte) bool {
-	return MatchRange(128, 191)(b)
+	return MatchRange(128, 191, b)
 }
 
 func isRTCP(buf []byte) bool {
 	// Not long enough to determine RTP/RTCP
 	if len(buf) < 4 {
 		return false
 	}
-
-	var rtcpPacketType uint8
-	r := bytes.NewReader([]byte{buf[1]})
-	if err := binary.Read(r, binary.BigEndian, &rtcpPacketType); err != nil {
-		return false
-	} else if rtcpPacketType >= 192 && rtcpPacketType <= 223 {
-		return true
-	}
-
-	return false
+	return buf[1] >= 192 && buf[1] <= 223
 }
 
 // MatchSRTP is a MatchFunc that only matches SRTP and not SRTCP