gosse - Go Server-Sent Events (SSE)

gosse is mainly intended as server-sided implementation of the SSE streaming concept. It comes with some (convenience) features like:

• out-of-the-box use with reasonable defaults
• options pattern to easily customize the behavior of the server
• channel concept to send events/messages only to certain clients

Example

The following code snippets show a fully working use case of gosse. Also take a look at the example files.

Client

The client (usually a web browser) connects to the backend server via the EventSource interface. It subscribes to channel_1 and prints the messages of type message (default type) and custom_event to the console log.

Server

The server implementation listens to and serves requests on port 13337 and allows CORS requests from any source. It alternately sends messages/events to

• all subscribed clients via Broadcast with the default event type
• all clients subscribed to channel_1 with the custom event type custom_event
• all clients subscribed to channel_2 with the custom event type custom_event

Output

When the server is running and the client connects successfully the developer console of your browser should show an output like that (the client will only receive broadcast messages and messages for channel_1):

event type -> custom_event | data -> channel_1: 1
event type -> message | data -> broadcast: 3
event type -> custom_event | data -> channel_1: 4
event type -> message | data -> broadcast: 6
event type -> custom_event | data -> channel_1: 7
event type -> message | data -> broadcast: 9
event type -> custom_event | data -> channel_1: 10
event type -> message | data -> broadcast: 12
event type -> custom_event | data -> channel_1: 13
[...]

Server Options

The server can be configured via options passed to the constructor.

Channel ID Extractor

The option WithChannelIDExtractor lets you set a custom implementation of the ChannelIDExtractor interface.

Default: Implementation that extracts the query parameter channel from the request and returns a nil error and http.StatusOK as http error code (only relevant when an error is returned).

Message To Bytes Converter

The option WithMessageToBytesConverter allows you to define the way Messages are converted to the byte slice sent to the client.

Default: Implementation

Channel Broker

The option WithChannelMessageBroker lets you use your custom implementation of the ChannelBroker interface with ChannelIdType as string and MessageType as Messager.

Default: Implementation

Message Store

The WithMessageStorer option allows the usage of a custom implementation of the MessageStorer interface.

Default: Nop implementation storing no messages for replay.

Message Replayer

The option WithMessageReplayer lets you define which messages are to be replayed for a client sending its last event id by implementing the MessageReplayer interface.

Default: Nop implementation returning no messages.

Additional Headers

The WithListenersAdditionalHeader option lets you define http headers that are sent to the client additionally to the default key Content-Type with value text/event-stream indicating SSE streaming.

Default: empty

Listeners Keep Alive Interval

The WithListenersKeepAliveInterval option allows you to define the time interval that is used to send periodic keep alive messages to a connected client. The keep alive interval only triggers when no other message is sent to the client in the given time span.

Default: 10 seconds.

Listeners Keep Alive Message

The option WithListenersKeepAliveMessage lets you define the keep alive message content.

Default: Simple message containing an empty comment line.