HTTP Server-Sent Events

forked from lorciv/sse

Sse is a Go package that implents HTTP server-sent events (SSE) handling. The standard for HTTP SSE can be found here.

$ go get github.com/WheeskyJack/sse

Usage

The package exposes a function NewStream that can be used to instantiate a Stream.

A Stream is a http.Handler, so it can be registered on a http.ServeMux. Clients that issue a GET request to the given path will receive events as they are sent by the server.

s := sse.NewStream()
http.Handle("/stream", s)

To send events on a stream, use the Send method. Send accepts the data to be sent as a slice of bytes.

s.Send(context.Background(), []byte("42"))

If you wish to specify the event type, use SendEvent instead. (A call to Send is equivalent to SendEvent with event type == "message".)

s.SendEvent(context.Background(), "apples", []byte("42"))

Arbitrarily complex data can be sent to the client as long as it is encoded as a byte slice. For example, structs can be encoded to json on the server using json.Marshal and then sent to the client.

Client example

Clients receive events as they are sent by the server.

For example, to implement Javascript client that runs in a browser, one can use use the EventSource object. The following code listens to the stream at url "/stream" (the one shown above) and prints the data on console as it arrives:

const stream = new EventSource('/stream');
stream.onmessage = function(m) {
    console.log(m.data);
};

Other functionalities

A stream can optionally be assigned a logger.

Buffering the input requests channel with desired size is possible.

send to client can be done concurrently and concurrency can be user controlled.

timeout for sending event to client can be controlled.