crud: more careful response process

In go-tarantool, crud API result decoding assumes that there are
always two response values, except for truncate. Such approach is based
on actual experience: success result is always `return res, nil`,
not `return res`. But this is not a feature guaranteed by crud
module API, just a current implementation quirk [1]
(since in Lua function result process there is no any difference).
See also similar patch in tarantool/python [2].

1. https://github.com/tarantool/crud/blob/53457477974fed42351cbd87f566d11e9f7e39bb/crud/common/schema.lua#L88
2. tarantool/tarantool-python@a4b734a

crud/result.go

@@ -70,12 +70,14 @@ func msgpackIsArray(code byte) bool {
 
 // DecodeMsgpack provides custom msgpack decoder.
 func (r *Result) DecodeMsgpack(d *msgpack.Decoder) error {
+	var retErr error
+
 	arrLen, err := d.DecodeArrayLen()
 	if err != nil {
 		return err
 	}
 
-	if arrLen < 2 {
+	if arrLen == 0 {
 		return fmt.Errorf("array len doesn't match: %d", arrLen)
 	}
 
@@ -130,27 +132,27 @@ func (r *Result) DecodeMsgpack(d *msgpack.Decoder) error {
 		}
 	}
 
-	code, err := d.PeekCode()
-	if err != nil {
-		return err
-	}
-
-	var retErr error
-	if msgpackIsArray(code) {
-		crudErr := newErrorMany(r.rowType)
-		if err := d.Decode(&crudErr); err != nil {
-			return err
-		}
-		retErr = *crudErr
-	} else if code != msgpcode.Nil {
-		crudErr := newError(r.rowType)
-		if err := d.Decode(&crudErr); err != nil {
+	if arrLen > 1 {
+		code, err := d.PeekCode()
+		if err != nil {
 			return err
 		}
-		retErr = *crudErr
-	} else {
-		if err := d.DecodeNil(); err != nil {
-			return err
+		if msgpackIsArray(code) {
+			crudErr := newErrorMany(r.rowType)
+			if err := d.Decode(&crudErr); err != nil {
+				return err
+			}
+			retErr = *crudErr
+		} else if code != msgpcode.Nil {
+			crudErr := newError(r.rowType)
+			if err := d.Decode(&crudErr); err != nil {
+				return err
+			}
+			retErr = *crudErr
+		} else {
+			if err := d.DecodeNil(); err != nil {
+				return err
+			}
 		}
 	}
 
@@ -175,18 +177,24 @@ func (r *NumberResult) DecodeMsgpack(d *msgpack.Decoder) error {
 		return err
 	}
 
-	if arrLen < 2 {
+	if arrLen == 0 {
 		return fmt.Errorf("array len doesn't match: %d", arrLen)
 	}
 
 	if r.Value, err = d.DecodeUint64(); err != nil {
 		return err
 	}
 
-	var crudErr *Error = nil
+	if arrLen > 1 {
+		var crudErr *Error = nil
 
-	if err := d.Decode(&crudErr); err != nil {
-		return err
+		if err := d.Decode(&crudErr); err != nil {
+			return err
+		}
+
+		if crudErr != nil {
+			return crudErr
+		}
 	}
 
 	for i := 2; i < arrLen; i++ {
@@ -195,10 +203,6 @@ func (r *NumberResult) DecodeMsgpack(d *msgpack.Decoder) error {
 		}
 	}
 
-	if crudErr != nil {
-		return crudErr
-	}
-
 	return nil
 }
 

crud/tarantool_test.go

@@ -254,71 +254,71 @@ var testGenerateDataCases = []struct {
 }{
 	{
 		"Insert",
-		2,
+		1,
 		1,
 		crud.MakeInsertRequest(spaceName).
 			Tuple(tuple).
 			Opts(simpleOperationOpts),
 	},
 	{
 		"InsertObject",
-		2,
+		1,
 		1,
 		crud.MakeInsertObjectRequest(spaceName).
 			Object(object).
 			Opts(simpleOperationObjectOpts),
 	},
 	{
 		"InsertMany",
-		2,
+		1,
 		10,
 		crud.MakeInsertManyRequest(spaceName).
 			Tuples(tuples).
 			Opts(opManyOpts),
 	},
 	{
 		"InsertObjectMany",
-		2,
+		1,
 		10,
 		crud.MakeInsertObjectManyRequest(spaceName).
 			Objects(objects).
 			Opts(opObjManyOpts),
 	},
 	{
 		"Replace",
-		2,
+		1,
 		1,
 		crud.MakeReplaceRequest(spaceName).
 			Tuple(tuple).
 			Opts(simpleOperationOpts),
 	},
 	{
 		"ReplaceObject",
-		2,
+		1,
 		1,
 		crud.MakeReplaceObjectRequest(spaceName).
 			Object(object).
 			Opts(simpleOperationObjectOpts),
 	},
 	{
 		"ReplaceMany",
-		2,
+		1,
 		10,
 		crud.MakeReplaceManyRequest(spaceName).
 			Tuples(tuples).
 			Opts(opManyOpts),
 	},
 	{
 		"ReplaceObjectMany",
-		2,
+		1,
 		10,
 		crud.MakeReplaceObjectManyRequest(spaceName).
 			Objects(objects).
 			Opts(opObjManyOpts),
 	},
 	{
 		"Upsert",
-		2,
+		1,
 		1,
 		crud.MakeUpsertRequest(spaceName).
 			Tuple(tuple).
@@ -327,7 +327,7 @@ var testGenerateDataCases = []struct {
 	},
 	{
 		"UpsertObject",
-		2,
+		1,
 		1,
 		crud.MakeUpsertObjectRequest(spaceName).
 			Object(object).
@@ -336,15 +336,15 @@ var testGenerateDataCases = []struct {
 	},
 	{
 		"UpsertMany",
-		2,
+		1,
 		10,
 		crud.MakeUpsertManyRequest(spaceName).
 			TuplesOperationsData(tuplesOperationsData).
 			Opts(opManyOpts),
 	},
 	{
 		"UpsertObjectMany",
-		2,
+		1,
 		10,
 		crud.MakeUpsertObjectManyRequest(spaceName).
 			ObjectsOperationsData(objectsOperationData).
@@ -475,7 +475,7 @@ func testCrudRequestCheck(t *testing.T, req tarantool.Request,
 
 	// resp.Data[0] - CRUD res.
 	// resp.Data[1] - CRUD err.
-	if expectedLen >= 2 {
+	if expectedLen >= 2 && resp.Data[1] != nil {
 		if crudErr, err := getCrudError(req, resp.Data[1]); err != nil {
 			t.Fatalf("Failed to get CRUD error: %#v", err)
 		} else if crudErr != nil {