encoder: Fix tuple wrt protocol version

- we can use EMPTY_TUPLE only if protocol >= 1
- also: if protocol >= 2 we can now use TUPLE{1,2,3} opcodes.

encode.go

@@ -165,16 +165,35 @@ func (e *Encoder) encode(rv reflect.Value) error {
 func (e *Encoder) encodeTuple(t Tuple) error {
 	l := len(t)
 
+	// protocol >= 2: [1-3]() -> TUPLE{1-3}
+	if e.config.Protocol >= 2 && (1 <= l && l <= 3) {
+		for i := range t {
+			err := e.encode(reflectValueOf(t[i]))
+			if err != nil {
+				return err
+			}
+		}
+
+		var op byte
 		switch l {
-	case 0:
-		return e.emit(opEmptyTuple)
+		case 1:
+			op = opTuple1
+		case 2:
+			op = opTuple2
+		case 3:
+			op = opTuple3
+		}
 
-	// TODO this are protocol 2 opcodes - check e.protocol before using them
-	//case 1:
-	//case 2:
-	//case 3:
+		return e.emit(op)
+	}
+
+	// protocol >= 1: ø tuple -> EMPTY_TUPLE
+	if e.config.Protocol >= 1 && l == 0 {
+		return e.emit(opEmptyTuple)
 	}
 
+	// general case: MARK ... TUPLE
+	// TODO detect cycles and double references to the same object
 	err := e.emit(opMark)
 	if err != nil {
 		return err

ogorek_test.go

@@ -176,19 +176,31 @@ var tests = []TestEntry{
 		//I("\x8b\x09\x00\x00\x00\xffm\xa1b\x86\xce\xfd\xaa\x00.")), // LONG4 TODO
 
 	X("tuple()", Tuple{},
-		I("(t.")), // MARK + TUPLE
+		P0("(t."),  // MARK + TUPLE
+		P1_(").")), // EMPTY_TUPLE
 
 	X("tuple((1,))", Tuple{int64(1)},
+		P0("(I1\nt."),     // MARK + TUPLE + INT
+		P1("(K\x01t."),    // MARK + TUPLE + BININT1
+		P2_("K\x01\x85."), // TUPLE1 + BININT1
 		I("I1\n\x85.")),   // TUPLE1 + INT
 
 	X("tuple((1,2))", Tuple{int64(1), int64(2)},
-		I("(I1\nI2\ntp0\n."), // MARK + TUPLE + INT
+		P0("(I1\nI2\nt."),      // MARK + TUPLE + INT
+		P1("(K\x01K\x02t."),    // MARK + TUPLE + BININT1
+		P2_("K\x01K\x02\x86."), // TUPLE2 + BININT1
 		I("I1\nI2\n\x86.")),    // TUPLE2 + INT
 
 	X("tuple((1,2,3))", Tuple{int64(1), int64(2), int64(3)},
+		P0("(I1\nI2\nI3\nt."),       // MARK + TUPLE + INT
+		P1("(K\x01K\x02K\x03t."),    // MARK + TUPLE + BININT1
+		P2_("K\x01K\x02K\x03\x87."), // TUPLE3 + BININT1
 		I("I1\nI2\nI3\n\x87.")),     // TUPLE3 + INT
 
 	X("tuple(((1,2), (3,4)))", Tuple{Tuple{int64(1), int64(2)}, Tuple{int64(3), int64(4)}},
+		P0("((I1\nI2\nt(I3\nI4\ntt."),            // MARK + INT + TUPLE
+		P1("((K\x01K\x02t(K\x03K\x04tt."),        // MARK + BININT1 + TUPLE
+		P2_("K\x01K\x02\x86K\x03K\x04\x86\x86."), // BININT1 + TUPLE2
 		I("((I1\nI2\ntp0\n(I3\nI4\ntp1\ntp2\n.")),
 
 	X("list([])", []interface{}{},