✨Accept canonical URL in proxy form

build-system/app-index/main.css

@@ -298,8 +298,12 @@ a.underlined::before {
   margin: 20px 0 0;
   font-size: 12px;
   text-align: right;
+  color: #888;
 }
-.form-info a {
+.form-info > span + a {
+  margin-left: 8px;
+}
+.form-info > a {
   font-weight: bold;
 }
 header {

build-system/app-index/proxy-form.js

@@ -36,6 +36,7 @@ module.exports = () => html`<div class="block">
           pattern="^(https?://)?[^\\s]+$" />
       </label>
       <div class="form-info">
+        <span>Takes canonical, AMPHTML and Google viewer URLs.</span>
         <a href="https://github.com/ampproject/amphtml/blob/master/contributing/TESTING.md#document-proxy"
           target="_blank">
           What's this?

build-system/app.js

@@ -119,19 +119,64 @@ app.get('/serve_mode_change', (req, res) => {
 //   - /proxy/?url=hello.com?mode=/shadow/ 👉 /shadow/proxy/s/hello.com
 //   - /proxy/?url=https://hello.com 👉 /proxy/s/hello.com
 //   - /proxy/?url=https://www.google.com/amp/s/hello.com 👉 /proxy/s/hello.com
+//   - /proxy/?url=hello.com/canonical 👉 /proxy/s/hello.com/amp
 //
 // This passthrough is useful to generate the URL from <form> values,
-// (See ./app-index/proxy-fom.js)
-app.get('/proxy', (req, res) => {
+// (See ./app-index/proxy-form.js)
+app.get('/proxy', async(req, res, next) => {
   const {mode, url} = req.query;
-  const prefix = (mode || '').replace(/\/$/, '');
-  const sufixClearPrefixReStr =
-      '^http(s?)://' +
+  const urlSuffixClearPrefixReStr =
+      '^https?://' +
       '((www\.)?google\.(com?|[a-z]{2}|com?\.[a-z]{2}|cat)/amp/s/)?';
-  const sufix = url.replace(new RegExp(sufixClearPrefixReStr, 'i'), '');
-  res.redirect(`${prefix}/proxy/s/${sufix}`);
+  const urlSuffix = url.replace(new RegExp(urlSuffixClearPrefixReStr, 'i'), '');
+
+  try {
+    const ampdocUrl = await requestAmphtmlDocUrl(urlSuffix);
+    const ampdocUrlSuffix = ampdocUrl.replace(/^https?:\/\//, '');
+    const modePrefix = (mode || '').replace(/\/$/, '');
+    const proxyUrl = `${modePrefix}/proxy/s/${ampdocUrlSuffix}`;
+    res.redirect(proxyUrl);
+  } catch ({message}) {
+    console.log(`ERROR: ${message}`);
+    next();
+  }
 });
 
+
+/**
+ * Resolves an AMPHTML URL from a canonical URL. If AMPHTML is canonical, same
+ * URL is returned.
+ * @param {string} urlSuffix URL without protocol or google.com/amp/s/...
+ * @param {string=} protocol 'https' or 'http'. 'https' retries using 'http'.
+ * @return {!Promise<string>}
+ */
+function requestAmphtmlDocUrl(urlSuffix, protocol = 'https') {
+  const defaultUrl = `${protocol}://${urlSuffix}`;
+  console.log(`Fetching URL: ${defaultUrl}`);
+  return new Promise((resolve, reject) => {
+    request(defaultUrl, (error, response, body) => {
+      if (error || (response && (
+        response.statusCode < 200 || response.statusCode >= 300))) {
+
+        if (protocol == 'https') {
+          return requestAmphtmlDocUrl(urlSuffix, 'http');
+        }
+        return reject(new Error(error || `Status: ${response.statusCode}`));
+      }
+      const {window} = new jsdom.JSDOM(body);
+      const linkRelAmphtml = window.document.querySelector('link[rel=amphtml]');
+      if (!linkRelAmphtml) {
+        return resolve(defaultUrl);
+      }
+      const amphtmlUrl = linkRelAmphtml.getAttribute('href');
+      if (!amphtmlUrl) {
+        return resolve(defaultUrl);
+      }
+      return resolve(amphtmlUrl);
+    });
+  });
+}
+
 /*
  * Intercept Recaptcha frame for,
  * integration tests. Using this to mock

contributing/TESTING.md

@@ -140,7 +140,9 @@ AMP ships with a local proxy for testing production AMP documents with the local
 
 For any public AMP document like: `http://output.jsbin.com/pegizoq/quiet`,
 
-You can access it with the local JS at
+You can access it with the local JS by using the form in
+[`http://localhost:8000`](http://localhost:8000) or by accessing the proxy URL
+directly:
 
 `http://localhost:8000/proxy/output.jsbin.com/pegizoq/quiet`.
 
@@ -327,13 +329,13 @@ If you are only testing a single file, you can use `gulp firebase --file=path/to
 
 ## End-to-End Tests
 
-You can run and create E2E tests locally during development. Currently tests only run on Chrome, but support for additional browsers is underway. These tests have not been added to our CI build yet - but they will be added soon. 
+You can run and create E2E tests locally during development. Currently tests only run on Chrome, but support for additional browsers is underway. These tests have not been added to our CI build yet - but they will be added soon.
 
-Run all tests with: 
+Run all tests with:
 ```
 gulp e2e
 ```
 
 The task will kick off `gulp build` and then `gulp serve` before running the tests. To skip building the runtime, use `--nobuild`.
 
-Create your own tests by adding them to `test\e2e` or `extensions\**\test-e2e`. For examples, see `test\e2e\test-github.js` and `extensions\amp-carousel\0.2\test-e2e\test-carousel.js`.
+Create your own tests by adding them to `test\e2e` or `extensions\**\test-e2e`. For examples, see `test\e2e\test-github.js` and `extensions\amp-carousel\0.2\test-e2e\test-carousel.js`.