fix: Handle string-valued error responses

github/github.go

@@ -1522,6 +1522,35 @@ type ErrorResponse struct {
 	DocumentationURL string `json:"documentation_url,omitempty"`
 }
 
+// UnmarshalJSON implements the json.Unmarshaler interface.
+func (r *ErrorResponse) UnmarshalJSON(data []byte) error {
+	type aliasErrorResponse ErrorResponse // avoid infinite recursion by using type alias.
+	response := struct {
+		Errors json.RawMessage `json:"errors"`
+		*aliasErrorResponse
+	}{
+		aliasErrorResponse: (*aliasErrorResponse)(r),
+	}
+
+	if err := json.Unmarshal(data, &response); err != nil {
+		return err
+	}
+	if len(response.Errors) == 0 || string(response.Errors) == "null" {
+		return nil
+	}
+	if err := json.Unmarshal(response.Errors, &r.Errors); err == nil {
+		return nil
+	}
+
+	var message string
+	if err := json.Unmarshal(response.Errors, &message); err != nil {
+		return err
+	}
+	//nolint:sliceofpointers
+	r.Errors = []Error{{Message: message}}
+	return nil
+}
+
 // ErrorBlock contains a further explanation for the reason of an error.
 // See https://developer.github.com/changes/2016-03-17-the-451-status-code-is-now-supported/
 // for more information.

github/github_test.go

@@ -4139,6 +4139,32 @@ func TestCheckResponse_unexpectedErrorStructure(t *testing.T) {
 	}
 }
 
+func TestCheckResponse_errorString(t *testing.T) {
+	t.Parallel()
+	httpBody := `{"message":"Forbidden","errors":"Repository level self-hosted runners are disabled on this repository","documentation_url":"https://docs.github.com/rest/actions/self-hosted-runners#create-a-registration-token-for-a-repository","status":"403"}`
+	res := &http.Response{
+		Request:    &http.Request{},
+		StatusCode: http.StatusForbidden,
+		Body:       io.NopCloser(strings.NewReader(httpBody)),
+	}
+	var err *ErrorResponse
+	errors.As(CheckResponse(res), &err)
+
+	if err == nil {
+		t.Fatal("Expected error response.")
+	}
+
+	want := &ErrorResponse{
+		Response:         res,
+		Message:          "Forbidden",
+		Errors:           []Error{{Message: "Repository level self-hosted runners are disabled on this repository"}},
+		DocumentationURL: "https://docs.github.com/rest/actions/self-hosted-runners#create-a-registration-token-for-a-repository",
+	}
+	if !errors.Is(err, want) {
+		t.Errorf("Error = %#v, want %#v", err, want)
+	}
+}
+
 // TestCheckResponse_LargeBodyTruncated verifies that CheckResponse reads at
 // most maxErrorBodySize bytes from an error response body, so that a
 // malicious or buggy server cannot cause the client to allocate unbounded