Response change({Map<String, String> headers, Map<String, Object> context, body})

Creates a new Response by copying existing values and applying specified changes.

New key-value pairs in context and headers will be added to the copied Response.

If context or headers includes a key that already exists, the key-value pair will replace the corresponding entry in the copied Response.

All other context and header values from the Response will be included in the copied Response unchanged.

body is the request body. It may be either a String or a Stream>.

Source 

Response change(
    {Map<String, String> headers, Map<String, Object> context, body}) {
  headers = updateMap(this.headers, headers);
  context = updateMap(this.context, context);

  if (body == null) body = getBody(this);

  return new Response(this.statusCode, body: body, headers: headers,
      context: context);
}