RemoteContextHelper: expose all request headers

Previously, we would manually update executor.sub.html to output request
headers into the HTML body. The result would be stored as a global
variable, window.requestHeaders, with absent headers having the string
value "absent".

This improves the situation in several ways:

* Adds a first-class API, getRequestHeaders(), to RemoteContextHelper,
  instead of relying on the implicit knowledge that if you use
  executeScript(), you can retrieve a global window.requestHeaders.

* The returned object is a Headers object, instead of an object literal.
  Absent headers are simply not in the object, instead of being the
  string "absent".

* The returned object has all request headers, not a manually-curated
  list.

* Because all headers are sent across the boundary at once, in the
  single getRequestHeaders() call, we no longer have to call into the
  remote context using executeScript() once per header of interest.

Bug: 1456579
Change-Id: I2c88fde4ed3007e712496f6ab807851e89ac6c6f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4778110
Reviewed-by: Fergal Daly <fergal@chromium.org>
Commit-Queue: Domenic Denicola <domenic@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1185025}

third_party/blink/web_tests/external/wpt/html/browsers/browsing-the-web/history-traversal/document-state.https.html

@@ -70,15 +70,14 @@
   // now-same-origin document initiating this navigation via history.
   await A.historyForward();
 
-  const secFetchSite = await B.executeScript(() => window.requestHeaders['sec-fetch-site']);
-  const referrer = await B.executeScript(() => window.requestHeaders['referer']);
+  const requestHeaders = await B.getRequestHeaders();
   const documentReferrer = await B.executeScript(() => document.referrer);
 
-  assert_equals(secFetchSite, 'cross-site',
+  assert_equals(requestHeaders.get('sec-fetch-site'), 'cross-site',
       'Same-origin forward history navigation to a document whose original ' +
       'initiator was cross-site, ends up with Sec-Fetch-Dest: cross-site ' +
       'header');
-  assert_equals(referrer, originA + '/',
+  assert_equals(requestHeaders.get('referer'), originA + '/',
       'Same-origin forward history navigation to a document whose original ' +
       'initiator was cross-site ends up with the Referer header that is the ' +
       'original cross-site initiator');
@@ -113,15 +112,14 @@
     location.reload();
   }, []);
 
-  const secFetchSite = await B.executeScript(() => window.requestHeaders['sec-fetch-site']);
-  const referrer = await B.executeScript(() => window.requestHeaders['referer']);
+  const requestHeaders = await B.getRequestHeaders();
   const documentReferrer = await B.executeScript(() => document.referrer);
 
-  assert_equals(secFetchSite, 'cross-site',
+  assert_equals(requestHeaders.get('sec-fetch-site'), 'cross-site',
       'Same-origin forward history navigation to a document whose original ' +
       'initiator was cross-site, ends up with Sec-Fetch-Dest: cross-site ' +
       'header');
-  assert_equals(referrer, originA + '/',
+  assert_equals(requestHeaders.get('referer'), originA + '/',
       'Same-origin forward history navigation to a document whose original ' +
       'initiator was cross-site ends up with the Referer header that is the ' +
       'original cross-site initiator');

third_party/blink/web_tests/external/wpt/html/browsers/browsing-the-web/remote-context-helper-tests/getRequestHeaders.window.js

@@ -0,0 +1,18 @@
+// META: title=RemoteContextHelper with defaults
+// META: script=/common/dispatcher/dispatcher.js
+// META: script=/common/get-host-info.sub.js
+// META: script=/common/utils.js
+// META: script=/html/browsers/browsing-the-web/remote-context-helper/resources/remote-context-helper.js
+// META: script=./resources/test-helper.js
+
+'use strict';
+
+promise_test(async t => {
+  const rcHelper = new RemoteContextHelper();
+  const main = await rcHelper.addWindow();
+
+  const headers = await main.getRequestHeaders();
+
+  assert_equals(headers.constructor, Headers);
+  assert_true(headers.has("user-agent"), "user-agent is present");
+});

third_party/blink/web_tests/external/wpt/html/browsers/browsing-the-web/remote-context-helper/resources/executor-window.py

@@ -0,0 +1,23 @@
+import json
+
+def main(request, response):
+  initRequestHeaders = ""
+  for header_name in request.headers.keys():
+    for header_value in request.headers.get_list(header_name):
+      js_name = json.dumps(header_name.lower().decode("utf-8"))
+      js_value = json.dumps(header_value.decode("utf-8"))
+      initRequestHeaders += f"window.__requestHeaders.append({js_name}, {js_value});\n"
+
+  return (200, [("Content-Type", "text/html")], f"""
+<!DOCTYPE HTML>
+<script src="/common/dispatcher/dispatcher.js"></script>
+<script src="./executor-common.js"></script>
+<script src="./executor-window.js"></script>
+
+<body>
+<script>
+window.__requestHeaders = new Headers();
+{initRequestHeaders}
+requestExecutor();
+</script>
+""")

third_party/blink/web_tests/external/wpt/html/browsers/browsing-the-web/remote-context-helper/resources/remote-context-helper.js

@@ -49,7 +49,7 @@
 {
   const RESOURCES_PATH =
       '/html/browsers/browsing-the-web/remote-context-helper/resources';
-  const WINDOW_EXECUTOR_PATH = `${RESOURCES_PATH}/executor.sub.html`;
+  const WINDOW_EXECUTOR_PATH = `${RESOURCES_PATH}/executor-window.py`;
   const WORKER_EXECUTOR_PATH = `${RESOURCES_PATH}/executor-worker.js`;
 
   /**
@@ -383,6 +383,26 @@
       });
     }
 
+    /**
+     * Gets a `Headers` object containing the request headers that were used
+     * when the browser requested this document.
+     *
+     * Currently, this only works for `RemoteContextHelper`s representing
+     * windows, not workers.
+     * @returns {Promise<Headers>}
+     */
+    async getRequestHeaders() {
+      // This only works in window environments for now. We could make it work
+      // for workers too; if you have a need, just share or duplicate the code
+      // that's in executor-window.py. Anyway, we explicitly use `window` in
+      // the script so that we get a clear error if you try using it on a
+      // worker.
+
+      // We need to serialize and deserialize the `Headers` object manually.
+      const asNestedArrays = await this.executeScript(() => [...window.__requestHeaders]);
+      return new Headers(asNestedArrays);
+    }
+
     /**
      * Executes a script in the remote context that will perform a navigation.
      * To do this safely, we must suspend the executor and wait for that to