sse: support Server Sent Event

docs/design/021-sse-api.md

@@ -0,0 +1,55 @@
+# Introduce an SSE API module for k6
+
+|                      |                                                              |
+|:---------------------|:-------------------------------------------------------------|
+| **author**           | @phymbert                                                    |
+| **status**           | 🔧 proposal                                                  |
+| **revisions**        | [initial](https://github.com/grafana/k6/pull/3639)           |
+| **Proof of concept** | [branch](https://github.com/phymbert/k6/tree/hp/feature/sse) |
+| **references**       | [#746](https://github.com/grafana/k6/issues/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](https://fr.wikipedia.org/wiki/Server-sent_events). 
+
+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
+
+```javascript
+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](https://github.com/grafana/k6/blob/d5cd1010ecb2381376188c8a47ab861cf8b5dc3d/js/modules/k6/experimental/sse/sse.go) developed with this proposal illustrates the feasibility and benefits of developing such an API.

examples/sse.js

@@ -0,0 +1,23 @@
+import sse from "k6/experimental/sse";
+import {check} from "k6";
+
+export default function () {
+	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});
+};

js/jsmodules.go

@@ -1,6 +1,7 @@
 package js
 
 import (
+	"go.k6.io/k6/js/modules/k6/experimental/sse"
 	"sync"
 
 	"go.k6.io/k6/ext"
@@ -45,6 +46,7 @@ func getInternalJSModules() map[string]interface{} {
 		"k6/experimental/tracing": tracing.New(),
 		"k6/experimental/browser": browser.New(),
 		"k6/experimental/fs":      fs.New(),
+		"k6/experimental/sse":     sse.New(),
 		"k6/net/grpc":             grpc.New(),
 		"k6/html":                 html.New(),
 		"k6/http":                 http.New(),