feat: report event source headers on open (#33)

Author: abarker-launchdarkly

.github/workflows/ci.yml

@@ -33,13 +33,13 @@ jobs:
           set -o pipefail
           make run-contract-tests | tee test-harness.log
       - name: Upload Test Service Logs
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         if: always()
         with:
           name: test-service-${{ matrix.node }}
           path: test-service.log
       - name: Upload Test Harness Logs
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         if: always()
         with:
           name: test-harness-${{ matrix.node }}

README.md

@@ -56,6 +56,18 @@ In a browser that is using native `EventSource` the extra argument would simply
 
 Like the standard `EventSource`, this implementation emits the event `open` when a stream has been started and `error` when a stream has failed for any reason. All events have a single parameter which is an instance of the `Event` class.
 
+The `open` event has the following extended behavior: the event object will have a `headers` property which is an object representing the HTTP response headers received when opening the stream. For example:
+
+```javascript
+{
+  'content-type': 'text/event-stream; charset=utf-8',
+  'transfer-encoding': 'chunked',
+  'connection': 'close',
+  'accept-ranges': 'bytes',
+  'cache-control': 'no-cache, no-store, must-revalidate',
+}
+```
+
 The `error` event has the following extended behavior: for an HTTP error response, the event object will have a `status` property (such as `401`) and optionally a `message` property (such as `"Unauthorized"`).
 
 ```javascript

lib/eventsource.js

@@ -252,7 +252,7 @@ function EventSource (url, eventSourceInitDict) {
         res.removeAllListeners('end')
         failOnce()
       })
-      _emit(new Event('open'))
+      _emit(new Event('open', { headers: res.headers }))
 
       // text/event-stream parser adapted from webkit's
       // Source/WebCore/page/EventSource.cpp

test/eventsource_test.js

@@ -59,10 +59,11 @@ async function expectNothingReceived (q) {
   assert.ok(q.isEmpty())
 }
 
-function writeEvents (chunks) {
+function writeEvents (chunks, headers = {}) {
+  const resHeaders = Object.assign({}, headers, { 'Content-Type': 'text/event-stream' })
   const q = new AsyncQueue()
   chunks.forEach(chunk => q.add(chunk))
-  return TestHttpHandlers.chunkedStream(200, {'Content-Type': 'text/event-stream'}, q)
+  return TestHttpHandlers.chunkedStream(200, resHeaders, q)
 }
 
 function assertRange (min, max, value) {
@@ -901,13 +902,13 @@ describe('Events', function () {
     })
   })
 
-  it('emits open event when connection is established', async () => {
+  it('emits open event with headers when connection is established', async () => {
     await withServer(async server => {
-      server.byDefault(writeEvents([]))
-
+      server.byDefault(writeEvents([], { 'X-LD-EnvId': '12345' }))
       await withEventSource(server, async es => {
         const e = await waitForOpenEvent(es)
         assert.equal(e.type, 'open')
+        assert.equal(e.headers['x-ld-envid'], '12345')
       })
     })
   })