fix: parse simple string based errors as part of the response (#1452)

A response can return a payload of the form:

```
{
  "ok": false,
  "error": "invalid_blocks",
  "errors": [
    "failed to match all allowed schemas [json-pointer:/blocks/3/text]",
    "invalid additional property: emoji [json-pointer:/blocks/3/text]"
  ],
  "response_metadata": {
    "messages": [
      "[ERROR] failed to match all allowed schemas [json-pointer:/blocks/3/text]",
      "[ERROR] invalid additional property: emoji [json-pointer:/blocks/3/text]"
    ]
  }
}
```

This means that we need to fallback to parsing a simple string if we
fail to parse the content of "errors" into a `map[string]interface{}`.

Closes #1446.

Author: nlopes

misc.go

@@ -45,6 +45,7 @@ func (t ConversationsInviteResponseError) Err() error {
 type SlackResponseErrors struct {
 	AppsManifestCreateResponseError  *AppsManifestCreateResponseError  `json:"-"`
 	ConversationsInviteResponseError *ConversationsInviteResponseError `json:"-"`
+	Message                          *string                           `json:"-"`
 }
 
 // MarshalJSON implements custom marshaling for SlackResponseErrors
@@ -55,6 +56,9 @@ func (e SlackResponseErrors) MarshalJSON() ([]byte, error) {
 	if e.ConversationsInviteResponseError != nil {
 		return json.Marshal(e.ConversationsInviteResponseError)
 	}
+	if e.Message != nil {
+		return json.Marshal(*e.Message)
+	}
 	return json.Marshal(nil)
 }
 
@@ -67,6 +71,15 @@ func (e *SlackResponseErrors) UnmarshalJSON(data []byte) error {
 	// Try to determine the error type by checking for unique fields
 	var raw map[string]interface{}
 	if err := json.Unmarshal(data, &raw); err != nil {
+		// If we can't unmarshal as object, try as string (fallback case)
+		//
+		// For more details on this specific problem look up issue
+		// https://github.com/slack-go/slack/issues/1446.
+		var stringError string
+		if stringErr := json.Unmarshal(data, &stringError); stringErr == nil {
+			e.Message = &stringError
+			return nil
+		}
 		return err
 	}
 

misc_test.go

@@ -133,6 +133,13 @@ func TestSlackResponseErrorsMarshaling(t *testing.T) {
 			},
 			expected: `{"error":"invalid_user","ok":false,"user":"U12345678"}`,
 		},
+		{
+			name: "StringError",
+			errors: SlackResponseErrors{
+				Message: func() *string { s := "failed to match all allowed schemas"; return &s }(),
+			},
+			expected: `"failed to match all allowed schemas"`,
+		},
 		{
 			name:     "EmptyErrors",
 			errors:   SlackResponseErrors{},
@@ -185,6 +192,16 @@ func TestSlackResponseErrorsUnmarshaling(t *testing.T) {
 			input:    `null`,
 			expected: SlackResponseErrors{},
 		},
+		{
+			name:  "StringError",
+			input: `"failed to match all allowed schemas [json-pointer:\\/blocks\\/3\\/text]"`,
+			expected: SlackResponseErrors{
+				Message: func() *string {
+					s := "failed to match all allowed schemas [json-pointer:\\/blocks\\/3\\/text]"
+					return &s
+				}(),
+			},
+		},
 	}
 
 	for _, tt := range tests {
@@ -210,6 +227,14 @@ func TestSlackResponseErrorsUnmarshaling(t *testing.T) {
 					t.Errorf("got %+v; want %+v", *errors.ConversationsInviteResponseError, *tt.expected.ConversationsInviteResponseError)
 				}
 			}
+
+			if tt.expected.Message != nil {
+				if errors.Message == nil {
+					t.Error("expected Message, got nil")
+				} else if *errors.Message != *tt.expected.Message {
+					t.Errorf("got %+v; want %+v", *errors.Message, *tt.expected.Message)
+				}
+			}
 		})
 	}
 }
@@ -256,6 +281,28 @@ func TestSlackResponseWithErrors(t *testing.T) {
 				Ok: true,
 			},
 		},
+		{
+			name:  "ResponseWithStringErrors",
+			input: `{"ok":false,"error":"invalid_blocks","errors":["failed to match all allowed schemas [json-pointer:\\/blocks\\/3\\/text]","invalid additional property: emoji [json-pointer:\\/blocks\\/3\\/text]"]}`,
+			expected: SlackResponse{
+				Ok:    false,
+				Error: "invalid_blocks",
+				Errors: []SlackResponseErrors{
+					{
+						Message: func() *string {
+							s := "failed to match all allowed schemas [json-pointer:\\/blocks\\/3\\/text]"
+							return &s
+						}(),
+					},
+					{
+						Message: func() *string {
+							s := "invalid additional property: emoji [json-pointer:\\/blocks\\/3\\/text]"
+							return &s
+						}(),
+					},
+				},
+			},
+		},
 	}
 
 	for _, tt := range tests {