peer_protocol: Improve piece decoding benchmark

peer_protocol/decoder_test.go

@@ -12,34 +12,42 @@ import (
 
 func BenchmarkDecodePieces(t *testing.B) {
 	r, w := io.Pipe()
+	const pieceLen = 1 << 14
 	msg := Message{
 		Type:  Piece,
 		Index: 0,
 		Begin: 1,
-		Piece: make([]byte, 1<<14),
+		Piece: make([]byte, pieceLen),
 	}
 	b, err := msg.MarshalBinary()
 	require.NoError(t, err)
 	t.SetBytes(int64(len(b)))
+	defer r.Close()
 	go func() {
+		defer w.Close()
 		for {
 			n, err := w.Write(b)
-			require.Equal(t, len(b), n)
+			if err == io.ErrClosedPipe {
+				return
+			}
 			require.NoError(t, err)
+			require.Equal(t, len(b), n)
 		}
 	}()
 	d := Decoder{
+		// Emulate what package torrent's client would do.
 		R:         bufio.NewReader(r),
 		MaxLength: 1 << 18,
 		Pool: &sync.Pool{
 			New: func() interface{} {
-				return make([]byte, 1<<14)
+				return make([]byte, pieceLen)
 			},
 		},
 	}
 	for range iter.N(t.N) {
 		var msg Message
 		require.NoError(t, d.Decode(&msg))
+		// WWJD
 		d.Pool.Put(msg.Piece)
 	}
 }