Custom marshalers

Marshaler implementations can implement optional additional methods to customize their behaviour beyond the methods required by the core interface.

Stream delimiters

By default, a streamed response delimits each response body with a single newline ("\n"). You can change this delimiter by having your marshaler implement Delimited.

For example, to separate each entry with a pipe ("|") instead:

type YourMarshaler struct {
  // ...
}

// ...

func (*YourMarshaler) Delimited() []byte {
  return []byte("|")
}

Stream content type

By default, a streamed response emits a Content-Type header that is the same for a unary response, from the ContentType() method of the Marshaler interface.

If you require the server to declare a distinct content type for stream responses versus unary responses, the marshaler must implement StreamContentType. This provides the MIME type when specifically responding to a streaming response.

For example, by default the JSONPb marshaler results in application/json for its Content-Type response header, irrespective of unary versus streaming. This can be changed for streaming endpoints by wrapping the marshaler with a custom marshaler that implements StreamContentType to return the NDJSON MIME type for streaming response endpoints:

type CustomJSONPb struct {
  runtime.JSONPb
}

func (*CustomJSONPb) Delimited() []byte {
  // Strictly speaking this is already the default delimiter for JSONPb, but
  // providing it here for completeness with an NDJSON marshaler all in one
  // place.
  return []byte("\n")
}

func (*CustomJSONPb) StreamContentType(interface{}) string {
  return "application/x-ndjson"
}