ampdoc: Add get/setMetaByName methods (#26609)

* ampdoc: Add get/setMetaByName methods

- Add getMetaByName to AmpDoc with overrides implemented in
  AmpDocSingle and AmpDocShadow to get the content value of a meta[name]
  tag.
- Add setMetaByName ot AmpDoc with override implemented in AmpDocShadow
  to store meta[name] tag content values.

* ampdoc: Correct jsdoc override

* ampdoc: Revisions based on review (relax)

- Simplify meta name/content lookups
- Add test for non-shadow getMetaByName

src/multidoc-manager.js

@@ -358,6 +358,9 @@ export class MultidocManager {
               // Ignore.
             } else if (name == 'viewport') {
               // Ignore.
+            } else if (name) {
+              // Store meta name/content pairs.
+              ampdoc.setMetaByName(name, n.getAttribute('content') || '');
             } else {
               // TODO(dvoytenko): copy other meta tags.
               dev().warn(TAG, 'meta ignored: ', n);

src/service/ampdoc-impl.js

@@ -24,6 +24,7 @@ import {
   removeDocumentVisibilityChangeListener,
 } from '../utils/document-visibility';
 import {dev, devAssert} from '../log';
+import {escapeCssSelectorIdent} from '../css';
 import {getParentWindowFrameElement, registerServiceBuilder} from '../service';
 import {getShadowRootNode} from '../shadow-embed';
 import {isDocumentReady, whenDocumentReady} from '../document-ready';
@@ -317,6 +318,9 @@ export class AmpDoc {
     /** @private {!Object<string, string>} */
     this.params_ = (opt_options && opt_options.params) || map();
 
+    /** @protected {!Object<string, string>} */
+    this.meta_ = (opt_options && opt_options.meta) || map();
+
     /** @private @const {!Array<string>} */
     this.declaredExtensions_ = [];
 
@@ -414,6 +418,38 @@ export class AmpDoc {
     return v == null ? null : v;
   }
 
+  /**
+   * Returns the value of an ampdoc's meta tag content for a given name, or
+   * `null` if the meta tag does not exist.
+   * @param {string} name
+   * @return {?string}
+   */
+  getMetaByName(name) {
+    if (!name) {
+      return null;
+    }
+
+    const el = dev()
+      .assertElement(this.win.document.head)
+      .querySelector(`meta[name="${escapeCssSelectorIdent(name)}"]`);
+
+    return el ? el.getAttribute('content') || '' : null;
+  }
+
+  /**
+   * Stores the value of an ampdoc's meta tag content for a given name. To be
+   * implemented by subclasses.
+   * @param {string} unusedName
+   * @param {string} unusedContent
+   *
+   * Avoid using this method in components. It is only meant to be used by the
+   * runtime for AmpDoc subclasses where <meta> elements do not exist and name/
+   * content pairs must be stored in this.meta_.
+   */
+  setMetaByName(unusedName, unusedContent) {
+    devAssert(null, 'not implemented');
+  }
+
   /**
    * Returns whether the specified extension has been declared on this ampdoc.
    * @param {string} extensionId
@@ -867,6 +903,22 @@ export class AmpDocShadow extends AmpDoc {
   whenReady() {
     return this.readyPromise_;
   }
+
+  /** @override */
+  getMetaByName(name) {
+    return this.meta_[name] !== undefined ? this.meta_[name] : null;
+  }
+
+  /** @override */
+  setMetaByName(name, content) {
+    if (!name) {
+      throw dev().createError(
+        'Attempted to store invalid meta name/content pair'
+      );
+    }
+
+    this.meta_[name] = content;
+  }
 }
 
 /**

test/unit/test-ampdoc.js

@@ -121,6 +121,14 @@ describes.sandboxed('AmpDocService', {}, () => {
       expect(service.getAmpDoc(div)).to.equal(service.getSingleDoc());
     });
 
+    it('should return meta content values', () => {
+      const meta = document.createElement('meta');
+      meta.setAttribute('name', 'abc');
+      meta.setAttribute('content', '123');
+      document.head.appendChild(meta);
+      expect(service.getAmpDoc(meta).getMetaByName('abc')).to.equal('123');
+    });
+
     // For example, <amp-next-page> creates shadow documents in single-doc
     // mode.
     describe('shadow documents', () => {

test/unit/test-runtime.js

@@ -1345,6 +1345,15 @@ describes.realWin(
         ).to.not.exist;
       });
 
+      it('should import meta content', () => {
+        const metaEl = win.document.createElement('meta');
+        metaEl.setAttribute('name', 'abc');
+        metaEl.setAttribute('content', '123');
+        importDoc.head.appendChild(metaEl);
+        const amp = win.AMP.attachShadowDoc(hostElement, importDoc, docUrl);
+        expect(amp.ampdoc.getMetaByName('abc')).to.equal('123');
+      });
+
       it('should start as visible by default', () => {
         win.AMP.attachShadowDoc(hostElement, importDoc, docUrl);
         expect(ampdoc.getVisibilityState()).to.equal('visible');