Packetcache: implement KeyframeSeqno and Get(nil).

packetcache/packetcache.go

@@ -362,15 +362,21 @@ func get(seqno uint16, entries []entry, result []byte) (uint16, uint32, bool) {
 		if entries[i].lengthAndMarker == 0 || entries[i].seqno != seqno {
 			continue
 		}
-		n := uint16(copy(
-			result[:entries[i].length()],
-			entries[i].buf[:]))
+		var n uint16
+		if len(result) > 0 {
+			n = uint16(copy(
+				result[:entries[i].length()],
+				entries[i].buf[:]))
+		} else {
+			n = entries[i].length()
+		}
 		return n, entries[i].timestamp, entries[i].marker()
 	}
 	return 0, 0, false
 }
 
-// Get retrieves a packet from the cache.
+// Get retrieves a packet from the cache, returns the number of bytes
+// copied.  If result is of length 0, returns the size of the packet.
 func (cache *Cache) Get(seqno uint16, result []byte) uint16 {
 	cache.mu.Lock()
 	defer cache.mu.Unlock()
@@ -394,8 +400,7 @@ func (cache *Cache) Last() (bool, uint16, uint32) {
 	if !cache.lastValid {
 		return false, 0, 0
 	}
-	buf := make([]byte, BufSize)
-	len, ts, _ := get(cache.last, cache.entries, buf)
+	len, ts, _ := get(cache.last, cache.entries, nil)
 	if len == 0 {
 		return false, 0, 0
 	}
@@ -436,6 +441,17 @@ func (cache *Cache) Keyframe() (uint32, bool, []uint16) {
 	return cache.keyframe.timestamp, cache.keyframe.complete, seqnos
 }
 
+func (cache *Cache) KeyframeSeqno() (bool, uint16, uint32) {
+	cache.mu.Lock()
+	defer cache.mu.Unlock()
+
+	if len(cache.keyframe.entries) == 0 {
+		return false, 0, 0
+	}
+
+	return true, cache.keyframe.entries[0].seqno, cache.keyframe.timestamp
+}
+
 func (cache *Cache) resize(capacity int) {
 	if len(cache.entries) == capacity {
 		return

packetcache/packetcache_test.go

@@ -44,6 +44,10 @@ func TestCache(t *testing.T) {
 	if !bytes.Equal(buf[:l], buf1) {
 		t.Errorf("Couldn't get 13")
 	}
+	l = cache.Get(13, nil)
+	if l != uint16(len(buf1)) {
+		t.Errorf("Couldn't retrieve length")
+	}
 	l = cache.GetAt(13, i1, buf)
 	if !bytes.Equal(buf[:l], buf1) {
 		t.Errorf("Couldn't get 13 at %v", i1)
@@ -170,6 +174,11 @@ func TestKeyframe(t *testing.T) {
 	packet := make([]byte, 1)
 	buf := make([]byte, BufSize)
 
+	found, _, _ := cache.KeyframeSeqno()
+	if found {
+		t.Errorf("Found keyframe in empty cache")
+	}
+
 	cache.Store(7, 57, true, false, packet)
 	if cache.keyframe.complete {
 		t.Errorf("Expected false, got true")
@@ -183,6 +192,12 @@ func TestKeyframe(t *testing.T) {
 	if ts != 57 || !c || len(kf) != 2 {
 		t.Errorf("Got %v %v %v, expected %v %v", ts, c, len(kf), 57, 2)
 	}
+
+	found, seqno, ts := cache.KeyframeSeqno()
+	if !found || seqno != 7 || ts != 57 {
+		t.Errorf("Got %v %v %v, expected %v %v", found, seqno, ts, 7, 57)
+	}
+
 	for _, i := range kf {
 		l := cache.Get(i, buf)
 		if int(l) != len(packet) {