json: switch backup and restore errors from string to struct types

This keeps backwards compatibility with the previous empty structs.
And maybe we'd want to put other fields into the inner struct later,
rather than the outer message.

doc/075_scripting.rst

@@ -139,7 +139,7 @@ Error
 +----------------------+-------------------------------------------+
 | ``message_type``     | Always "error"                            |
 +----------------------+-------------------------------------------+
-| ``error``            | Error message                             |
+| ``error.message``    | Error message                             |
 +----------------------+-------------------------------------------+
 | ``during``           | What restic was trying to do              |
 +----------------------+-------------------------------------------+
@@ -539,6 +539,19 @@ Status
 |``bytes_skipped``     | Total size of skipped files                                |
 +----------------------+------------------------------------------------------------+
 
+Error
+^^^^^
+
++----------------------+-------------------------------------------+
+| ``message_type``     | Always "error"                            |
++----------------------+-------------------------------------------+
+| ``error.message``    | Error message                             |
++----------------------+-------------------------------------------+
+| ``during``           | Always "restore"                          |
++----------------------+-------------------------------------------+
+| ``item``             | Usually, the path of the problematic file |
++----------------------+-------------------------------------------+
+
 Verbose Status
 ^^^^^^^^^^^^^^
 

internal/ui/backup/json.go

@@ -67,7 +67,7 @@ func (b *JSONProgress) Update(total, processed Counter, errors uint, currentFile
 func (b *JSONProgress) ScannerError(item string, err error) error {
 	b.error(errorUpdate{
 		MessageType: "error",
-		Error:       err.Error(),
+		Error:       errorObject{err.Error()},
 		During:      "scan",
 		Item:        item,
 	})
@@ -78,7 +78,7 @@ func (b *JSONProgress) ScannerError(item string, err error) error {
 func (b *JSONProgress) Error(item string, err error) error {
 	b.error(errorUpdate{
 		MessageType: "error",
-		Error:       err.Error(),
+		Error:       errorObject{err.Error()},
 		During:      "archival",
 		Item:        item,
 	})
@@ -205,9 +205,13 @@ type statusUpdate struct {
 	CurrentFiles     []string `json:"current_files,omitempty"`
 }
 
+type errorObject struct {
+	Message string `json:"message"`
+}
+
 type errorUpdate struct {
 	MessageType string      `json:"message_type"` // "error"
-	Error       string `json:"error"`
+	Error       errorObject `json:"error"`
 	During      string      `json:"during"`
 	Item        string      `json:"item"`
 }

internal/ui/backup/json_test.go

@@ -17,11 +17,11 @@ func createJSONProgress() (*ui.MockTerminal, ProgressPrinter) {
 func TestJSONError(t *testing.T) {
 	term, printer := createJSONProgress()
 	test.Equals(t, printer.Error("/path", errors.New("error \"message\"")), nil)
-	test.Equals(t, []string{"{\"message_type\":\"error\",\"error\":\"error \\\"message\\\"\",\"during\":\"archival\",\"item\":\"/path\"}\n"}, term.Errors)
+	test.Equals(t, []string{"{\"message_type\":\"error\",\"error\":{\"message\":\"error \\\"message\\\"\"},\"during\":\"archival\",\"item\":\"/path\"}\n"}, term.Errors)
 }
 
 func TestJSONScannerError(t *testing.T) {
 	term, printer := createJSONProgress()
 	test.Equals(t, printer.ScannerError("/path", errors.New("error \"message\"")), nil)
-	test.Equals(t, []string{"{\"message_type\":\"error\",\"error\":\"error \\\"message\\\"\",\"during\":\"scan\",\"item\":\"/path\"}\n"}, term.Errors)
+	test.Equals(t, []string{"{\"message_type\":\"error\",\"error\":{\"message\":\"error \\\"message\\\"\"},\"during\":\"scan\",\"item\":\"/path\"}\n"}, term.Errors)
 }

internal/ui/restore/json.go

@@ -48,7 +48,7 @@ func (t *jsonPrinter) Update(p State, duration time.Duration) {
 func (t *jsonPrinter) Error(item string, err error) error {
 	t.error(errorUpdate{
 		MessageType: "error",
-		Error:       err.Error(),
+		Error:       errorObject{err.Error()},
 		During:      "restore",
 		Item:        item,
 	})
@@ -113,9 +113,13 @@ type statusUpdate struct {
 	BytesSkipped   uint64  `json:"bytes_skipped,omitempty"`
 }
 
+type errorObject struct {
+	Message string `json:"message"`
+}
+
 type errorUpdate struct {
 	MessageType string      `json:"message_type"` // "error"
-	Error       string `json:"error"`
+	Error       errorObject `json:"error"`
 	During      string      `json:"during"`
 	Item        string      `json:"item"`
 }

internal/ui/restore/json_test.go

@@ -66,5 +66,5 @@ func TestJSONPrintCompleteItem(t *testing.T) {
 func TestJSONError(t *testing.T) {
 	term, printer := createJSONProgress()
 	test.Equals(t, printer.Error("/path", errors.New("error \"message\"")), nil)
-	test.Equals(t, []string{"{\"message_type\":\"error\",\"error\":\"error \\\"message\\\"\",\"during\":\"restore\",\"item\":\"/path\"}\n"}, term.Errors)
+	test.Equals(t, []string{"{\"message_type\":\"error\",\"error\":{\"message\":\"error \\\"message\\\"\"},\"during\":\"restore\",\"item\":\"/path\"}\n"}, term.Errors)
 }