What a handler may return inside {:ok, _}.

Plain values

Any JSON-encodable term (map, list, binary, number, nil, boolean) is encoded with JSON and sent with Content-Type: application/json. This is what most handlers return.

%Mayfly.Response{}

Use the struct when you need control over the content type or want to stream:

# raw bytes, custom content type
%Mayfly.Response{body: png, content_type: "image/png"}

# streamed: any Enumerable of iodata (Stream, list, ...)
%Mayfly.Response{body: Stream.map(tokens, &chunk/1), content_type: "text/event-stream"}
|> Mayfly.Response.stream()

# streamed through a Function URL with status/headers:
%Mayfly.Response{body: stream}
|> Mayfly.Response.stream()
|> Mayfly.Response.http(status: 200, headers: %{"content-type" => "text/plain"}, cookies: [])

Streaming requires the function to be invoked with RESPONSE_STREAM invoke mode (Function URLs) or InvokeWithResponseStream. Chunks are written synchronously; if Lambda stops reading (bandwidth cap, disconnected client) the producer blocks. send_timeout (ms, default 30 000) bounds a single stalled write, after which the stream is aborted. Errors raised while the stream is being consumed are reported to Lambda via HTTP trailers and forwarded to the client as error metadata; the response is otherwise treated as successful, so validate early and fail before the first chunk if you can.