021-sse-api.md

Introduce an SSE API module for k6

author	@phymbert
status	🔧 proposal
revisions	initial
Proof of concept	branch
references	#746

Problem definition

The current version of k6 reads the full http response body before returning to the client, which make impossible testing Server-Sent Event.

We propose to introduce a new sse module. This module is intended to offer an intuitive and user-friendly API for SSE interactions within k6 scripts.

Proposed solution

We suggest to implement a minimalist, experimental (sse) module based on the go http client. The new module will allow users to interact with SSE. The module will provide an open which will allow the user to pass a setup function to configure an event callback as it is done in the ws module with message.

Limitation

The module will not support async io and the javascript main loop will be blocked during the http request duration.

Example usage

import sse from 'k6/experimental/sse';

var url = "https://echo.websocket.org/.sse";
var params = {"tags": {"my_tag": "hello"}};

var response = sse.open(url, params, function (client) {
    client.on('open', function open() {
        console.log('connected');
    });

    client.on('event', function (event) {
        console.log(`event id=${event.id}, name=${event.name}, data=${event.data}`);
    });

    client.on('error', function (e) {
        console.log('An unexpected error occurred: ', e.error());
    });
});

check(response, {"status is 200": (r) => r && r.status === 200});

Conclusion

We believe the proof of concept developed with this proposal illustrates the feasibility and benefits of developing such an API.