Add tests for CORS-unsafe Last-Event-ID in EventSource

Author: rexxars

eventsource/eventsource-cross-origin-preflight.window.js

@@ -0,0 +1,33 @@
+// META: title=EventSource: cross-origin preflight
+// META: script=/common/utils.js
+
+const crossdomain = location.href.replace('://', '://élève.').replace(/\/[^\/]*$/, '/')
+const origin = location.origin.replace('://', '://xn--lve-6lad.')
+
+;[
+  ['safe `last-event-id` (no preflight)', 'safe'],
+  ['unsafe `last-event-id` (too long)', 'long'],
+  ['unsafe `last-event-id` (unsafe characters)', 'unsafe']
+].forEach(([name, fixture]) => {
+  async_test(document.title + ' - ' + name).step(function() {
+    const uuid = token()
+    const url = crossdomain + 'resources/cors-unsafe-last-event-id.py?fixture=' + fixture + '&token=' + uuid
+
+    const source = new EventSource(url)
+
+    // Make sure to close the EventSource after the test is done.
+    this.add_cleanup(() => source.close())
+
+    // 1. Event will be a `message` with `id` set to a CORS-safe value, then disconnects.
+    source.addEventListener('message', this.step_func(e => assert_equals(e.data, fixture)))
+
+    // 2. Will emit either `success` or `failure` event. We expect `success`,
+    //    which is the case if `last-event-id` is set to the same value as received above,
+    //    and a preflight request has been sent for the unsafe `last-event-id` headers.
+    source.addEventListener('success', this.step_func_done())
+    source.addEventListener('failure', (evt) => {
+      this.step(() => assert_unreached(evt.data))
+      this.done()
+    })
+  })
+})

eventsource/resources/cors-unsafe-last-event-id.py

@@ -0,0 +1,96 @@
+from datetime import datetime
+
+# Beyond the 128-byte limit for `Last-Event-ID`
+long_string = b"a" * 255
+
+# A regular, safe `Last-Event-ID` value
+safe_id_value = b"abc"
+
+# CORS-unsafe request-header byte 0x3C (`<`) in `Last-Event-ID`
+unsafe_id_value = b"e5p3n<3k0k0s"
+
+def main(request, response):
+  origin = request.headers.get(b"Origin")
+  cors_request_headers = request.headers.get(b"Access-Control-Request-Headers")
+  
+  # Allow any CORS origin
+  if origin is not None:
+    response.headers.set(b"Access-Control-Allow-Origin", origin)
+
+  # Allow any CORS request headers
+  if cors_request_headers is not None: 
+    response.headers.set(b"Access-Control-Allow-Headers", cors_request_headers)
+
+  # Expect a `token` in the query string
+  if b"token" not in request.GET:
+    headers = [(b"Content-Type", b"text/plain")]
+    return 400, headers, b"ERROR: `token` query parameter!"
+
+  # Expect a `fixture` in the query string
+  if b"fixture" not in request.GET:
+    headers = [(b"Content-Type", b"text/plain")]
+    return 400, headers, b"ERROR: `fixture` query parameter!"
+
+  # Prepare state
+  fixture = request.GET.first(b"fixture")
+  token = request.GET.first(b"token")
+  last_event_id = request.headers.get(b"Last-Event-ID", b"")
+  expect_preflight = fixture == b"unsafe" or fixture == b"long"
+
+  # Preflight handling
+  if request.method == u"OPTIONS":
+    # The first request (without any `Last-Event-ID` header) should _never_ be a
+    # preflight request, since it should be considered a "safe" request.
+    # If we _do_ send a preflight for these requests, error early.
+    if last_event_id == b"":
+      headers = [(b"Content-Type", b"text/plain")]
+      return 400, headers, b"ERROR: No Last-Event-ID header in preflight!"
+
+    # We keep track of the different "tokens" we see, in order to tell whether or not
+    # a client has done a preflight request. If the "stash" does not contain a token,
+    # no preflight request was made.
+    request.server.stash.put(token, cors_request_headers)
+    
+    # We can return with an empty body on preflight requests
+    return b""
+
+  # This will be a SSE endpoint
+  response.headers.set(b"Content-Type", b"text/event-stream")
+  response.headers.set(b"Cache-Control", b"no-store")
+
+  # If we do not have a `Last-Event-ID` header, we're on the initial request
+  # Respond with the fixture corresponding to the `fixture` query parameter
+  if last_event_id == b"":
+    if fixture == b"safe":
+      return b"id: " + safe_id_value + b"\nretry: 200\ndata: safe\n\n"
+    if fixture == b"unsafe":
+      return b"id: " + unsafe_id_value + b"\nretry: 200\ndata: unsafe\n\n"
+    if fixture == b"long":
+      return b"id: " + long_string + b"\nretry: 200\ndata: long\n\n"
+    return b"event: failure\ndata: unknown fixture\n\n"
+
+  # If we have a `Last-Event-ID` header, we're on a reconnect.
+  # If fixture is "unsafe", eg requires a preflight, check to see that we got one.
+  preflight_headers = request.server.stash.take(token)
+  saw_preflight = preflight_headers is not None
+  if saw_preflight and not expect_preflight: 
+    return b"event: failure\ndata: saw preflight, did not expect one\n\n"
+  elif not saw_preflight and expect_preflight:
+    return b"event: failure\ndata: expected preflight, did not get one\n\n"
+
+  if saw_preflight and preflight_headers.lower() != b"last-event-id":
+    data = b"preflight `access-control-request-headers` was not `last-event-id`"
+    return b"event: failure\ndata: " + data + b"\n\n"
+
+  # Expect to have the same ID in the header as the one we sent.
+  expected = b"<unknown>"
+  if fixture == b"safe":
+    expected = safe_id_value
+  elif fixture == b"unsafe":
+    expected = unsafe_id_value
+  elif fixture == b"long":
+    expected = long_string
+  
+  event = last_event_id == expected and b"success" or b"failure"
+  data = b"got " + last_event_id + b", expected " + expected
+  return b"event: " + event + b"\ndata: " + data + b"\n\n"