encoder: Fix struct encoding wrt protocol version

Similarly to dict, for struct encoding switch from protocol 1 opcodes
into always using protocol 0 opcodes, which is by the way 1 byte
shorter.

For the reference - for structs, unlike maps, the order of emitted keys
is well-defined - it is the order of fields as they are defined in the
struct. This way we can precisely test encoder output on structs with
more than 1 field.

encode.go

@@ -466,7 +466,7 @@ func (e *Encoder) encodeStruct(st reflect.Value) error {
 
 	structTags := getStructTags(st)
 
-	err := e.emit(opEmptyDict, opMark)
+	err := e.emit(opMark)
 	if err != nil {
 		return err
 	}
@@ -503,7 +503,7 @@ func (e *Encoder) encodeStruct(st reflect.Value) error {
 		}
 	}
 
-	return e.emit(opSetitems)
+	return e.emit(opDict)
 }
 
 func reflectValueOf(v interface{}) reflect.Value {

ogorek_test.go

@@ -331,7 +331,16 @@ var tests = []TestEntry{
 		[]interface{}{map[interface{}]interface{}{"Foo": "Qux", "Bar": int64(4)}},
 
 		// MARK + STRING + INT + DICT + LIST
-		I("((S\"Foo\"\nS\"Qux\"\nS\"Bar\"\nI4\ndl.")),
+		P0("((S\"Foo\"\nS\"Qux\"\nS\"Bar\"\nI4\ndl."),
+
+		// MARK + SHORT_BINSTRING + BININT1 + DICT + LIST
+		P12("((U\x03FooU\x03QuxU\x03BarK\x04dl."),
+
+		// MARK + BINUNICODE + BININT1 + DICT + LIST
+		P3("((X\x03\x00\x00\x00FooX\x03\x00\x00\x00QuxX\x03\x00\x00\x00BarK\x04dl."),
+
+		// MARK + SHORT_BINUNICODE + BININT1 + DICT + LIST
+		P4_("((\x8c\x03Foo\x8c\x03Qux\x8c\x03BarK\x04dl.")),
 }
 
 // foo is a type to test how encoder handles Go structs.