Upgraded feedkit's handling of stream sources

sources/stream_errors.go

@@ -0,0 +1,63 @@
+package sources
+
+import "errors"
+
+type streamRetryableError struct {
+	err error
+}
+
+func (e *streamRetryableError) Error() string {
+	if e.err == nil {
+		return "retryable stream error"
+	}
+	return e.err.Error()
+}
+
+func (e *streamRetryableError) Unwrap() error { return e.err }
+
+type streamFatalError struct {
+	err error
+}
+
+func (e *streamFatalError) Error() string {
+	if e.err == nil {
+		return "fatal stream error"
+	}
+	return e.err.Error()
+}
+
+func (e *streamFatalError) Unwrap() error { return e.err }
+
+// StreamRetryable marks a stream-source exit as retryable.
+func StreamRetryable(err error) error {
+	if err == nil {
+		return nil
+	}
+	return &streamRetryableError{err: err}
+}
+
+// StreamFatal marks a stream-source exit as fatal.
+func StreamFatal(err error) error {
+	if err == nil {
+		return nil
+	}
+	return &streamFatalError{err: err}
+}
+
+// IsStreamRetryable reports whether err contains a retryable stream marker.
+func IsStreamRetryable(err error) bool {
+	if err == nil {
+		return false
+	}
+	var target *streamRetryableError
+	return errors.As(err, &target)
+}
+
+// IsStreamFatal reports whether err contains a fatal stream marker.
+func IsStreamFatal(err error) bool {
+	if err == nil {
+		return false
+	}
+	var target *streamFatalError
+	return errors.As(err, &target)
+}