crud: support operation_data field in errors

This patch adds `operation_data` decoding for the `crud.Error`.

The `operation_data` type is determined as `rowType` in `crud.Result`.

Also, according to [1], an error can contain one of the following:
- an error
- an array of errors
- nil

So the error decoding logic has been modified to consider each case,
in order to avoid comparing an error to nil.

1. https://github.com/tarantool/crud/tree/master#api

Closes #330

Author: askalt

CHANGELOG.md

@@ -16,6 +16,7 @@ Versioning](http://semver.org/spec/v2.0.0.html) except to the first release.
 - More linters on CI (#310)
 - Meaningful description for read/write socket errors (#129)
 - Support password and password file to decrypt private SSL key file (#319)
+- Support `operation_data` in `crud.Error` (#330) 
 
 ### Changed
 

crud/error.go

@@ -1,6 +1,7 @@
 package crud
 
 import (
+	"reflect"
 	"strings"
 
 	"github.com/vmihailenco/msgpack/v5"
@@ -21,6 +22,15 @@ type Error struct {
 	Stack string
 	// Str is the text of reason with error class.
 	Str string
+	// OperationData is the object/tuple with which an error occurred.
+	OperationData interface{}
+	// operationDataType contains the type of OperationData.
+	operationDataType reflect.Type
+}
+
+// newError creates an Error object with a custom operation data type to decoding.
+func newError(operationDataType reflect.Type) *Error {
+	return &Error{operationDataType: operationDataType}
 }
 
 // DecodeMsgpack provides custom msgpack decoder.
@@ -59,6 +69,20 @@ func (e *Error) DecodeMsgpack(d *msgpack.Decoder) error {
 			if e.Str, err = d.DecodeString(); err != nil {
 				return err
 			}
+		case "operation_data":
+			if e.operationDataType != nil {
+				tuple := reflect.New(e.operationDataType)
+				if err = d.DecodeValue(tuple); err != nil {
+					return err
+				}
+				e.OperationData = tuple.Elem().Interface()
+			} else {
+				var decoded interface{}
+				if err = d.Decode(&decoded); err != nil {
+					return err
+				}
+				e.OperationData = decoded
+			}
 		default:
 			if err := d.Skip(); err != nil {
 				return err
@@ -77,6 +101,13 @@ func (e Error) Error() string {
 // ErrorMany describes CRUD error object for `_many` methods.
 type ErrorMany struct {
 	Errors []Error
+	// operationDataType contains the type of OperationData for each Error.
+	operationDataType reflect.Type
+}
+
+// newErrorMany creates an ErrorMany object with a custom operation data type to decoding.
+func newErrorMany(operationDataType reflect.Type) *ErrorMany {
+	return &ErrorMany{operationDataType: operationDataType}
 }
 
 // DecodeMsgpack provides custom msgpack decoder.
@@ -88,16 +119,15 @@ func (e *ErrorMany) DecodeMsgpack(d *msgpack.Decoder) error {
 
 	var errs []Error
 	for i := 0; i < l; i++ {
-		var crudErr *Error = nil
+		crudErr := newError(e.operationDataType)
 		if err := d.Decode(&crudErr); err != nil {
 			return err
-		} else if crudErr != nil {
-			errs = append(errs, *crudErr)
 		}
+		errs = append(errs, *crudErr)
 	}
 
 	if len(errs) > 0 {
-		*e = ErrorMany{Errors: errs}
+		e.Errors = errs
 	}
 
 	return nil

crud/example_test.go

@@ -78,6 +78,43 @@ func ExampleResult_rowsCustomType() {
 	// [{{} 2010 45 bla}]
 }
 
+func ExampleResult_operationDataCustomType() {
+	conn := exampleConnect()
+	req := crud.MakeInsertManyRequest(exampleSpace).Tuples([]interface{}{
+		[]interface{}{uint(1), 1, "bla"},
+		[]interface{}{uint(1), 2, "blabla"},
+		[]interface{}{uint(2011), 3, nil},
+	})
+
+	type Tuple struct {
+		_msgpack struct{} `msgpack:",asArray"` //nolint: structcheck,unused
+		Id       uint64
+		BucketId uint64
+		Name     string
+	}
+
+	ret := crud.MakeResult(reflect.TypeOf(Tuple{}))
+	if err := conn.Do(req).GetTyped(&ret); err != nil {
+		crudErrs := err.(crud.ErrorMany)
+		// We need to trim the error message to make the example repeatable.
+		errmsg := crudErrs.Error()[:10]
+		fmt.Printf("Failed to execute request: %s\n", errmsg)
+		fmt.Println("Erroneous data:")
+		for _, crudErr := range crudErrs.Errors {
+			operationData := crudErr.OperationData.(Tuple)
+			fmt.Println(operationData)
+		}
+	} else {
+		fmt.Println(ret.Metadata)
+		fmt.Println(ret.Rows)
+	}
+	// Output:
+	// Failed to execute request: CallError:
+	// Erroneous data:
+	// {{} 1 2 blabla}
+	// {{} 2011 3 }
+}
+
 // ExampleResult_many demonstrates that there is no difference in a
 // response from *ManyRequest.
 func ExampleResult_many() {

crud/result.go

@@ -137,21 +137,17 @@ func (r *Result) DecodeMsgpack(d *msgpack.Decoder) error {
 
 	var retErr error
 	if msgpackIsArray(code) {
-		var crudErr *ErrorMany
+		crudErr := newErrorMany(r.rowType)
 		if err := d.Decode(&crudErr); err != nil {
 			return err
 		}
-		if crudErr != nil {
-			retErr = *crudErr
-		}
-	} else {
-		var crudErr *Error
+		retErr = *crudErr
+	} else if code != msgpcode.Nil {
+		crudErr := newError(r.rowType)
 		if err := d.Decode(&crudErr); err != nil {
 			return err
 		}
-		if crudErr != nil {
-			retErr = *crudErr
-		}
+		retErr = *crudErr
 	}
 
 	for i := 2; i < arrLen; i++ {