Make packetcache.Get use a caller-allocated buffer.

packetcache/packetcache.go

@@ -115,7 +115,7 @@ func (cache *Cache) Expect(n int) {
 	cache.expected += uint32(n)
 }
 
-func (cache *Cache) Get(seqno uint16) []byte {
+func (cache *Cache) Get(seqno uint16, result []byte) uint16 {
 	cache.mu.Lock()
 	defer cache.mu.Unlock()
 
@@ -124,11 +124,12 @@ func (cache *Cache) Get(seqno uint16) []byte {
 			cache.entries[i].seqno != seqno {
 			continue
 		}
-		buf := make([]byte, cache.entries[i].length)
-		copy(buf, cache.entries[i].buf[:])
-		return buf
+		return uint16(copy(
+			result[:cache.entries[i].length],
+			cache.entries[i].buf[:]),
+		)
 	}
-	return nil
+	return 0
 }
 
 // Shift 17 bits out of the bitmap.  Return a boolean indicating if any

packetcache/packetcache_test.go

@@ -23,13 +23,20 @@ func TestCache(t *testing.T) {
 	cache.Store(13, buf1)
 	cache.Store(17, buf2)
 
-	if bytes.Compare(cache.Get(13), buf1) != 0 {
+	buf := make([]byte, BufSize)
+
+	l := cache.Get(13, buf)
+	if bytes.Compare(buf[:l], buf1) != 0 {
 		t.Errorf("Couldn't get 13")
 	}
-	if bytes.Compare(cache.Get(17), buf2) != 0 {
+
+	l = cache.Get(17, buf)
+	if bytes.Compare(buf[:l], buf2) != 0 {
 		t.Errorf("Couldn't get 17")
 	}
-	if cache.Get(42) != nil {
+
+	l = cache.Get(42, buf)
+	if l != 0 {
 		t.Errorf("Creation ex nihilo")
 	}
 }
@@ -42,14 +49,15 @@ func TestCacheOverflow(t *testing.T) {
 	}
 
 	for i := 0; i < 32; i++ {
-		buf := cache.Get(uint16(i))
+		buf := make([]byte, BufSize)
+		l := cache.Get(uint16(i), buf)
 		if i < 16 {
-			if buf != nil {
+			if l > 0 {
 				t.Errorf("Creation ex nihilo: %v", i)
 			}
 		} else {
-			if len(buf) != 1 || buf[0] != uint8(i) {
-				t.Errorf("Expected [%v], got %v", i, buf)
+			if l != 1 || buf[0] != uint8(i) {
+				t.Errorf("Expected [%v], got %v", i, buf[:l])
 			}
 		}
 	}