Add description and icon to preview URLs for non-document resources g…

…ristlabs#1242

When pasting a URL in some app or website that allows previewing the
link, for other resources than documents, you were offered an irrelevant
description. This patches aims to give a generic description of what is
Grist.

app/server/lib/sendAppPage.ts

@@ -157,8 +157,8 @@ export function makeSendAppPage({ server, staticDir, tag, testLogin, baseDomain
     const staticTag = options.tag || tag;
     // If boot tag is used, serve assets locally, otherwise respect
     // APP_STATIC_URL.
-    const staticOrigin = staticTag === 'boot' ? '' : (process.env.APP_STATIC_URL || '');
-    const staticBaseUrl = `${staticOrigin}/v/${staticTag}/`;
+    const staticOrigin = staticTag === 'boot' ? '' : (process.env.APP_STATIC_URL || config.homeUrl || '');
+    const staticBaseUrl = new URL(`/v/${staticTag}/`, staticOrigin).href;
     const customHeadHtmlSnippet = server.create.getExtraHeadHtml?.() ?? "";
     const warning = testLogin ? "<div class=\"dev_warning\">Authentication is not enforced</div>" : "";
     // Preload all languages that will be used or are requested by client.
@@ -173,7 +173,7 @@ export function makeSendAppPage({ server, staticDir, tag, testLogin, baseDomain
     const content = fileContent
       .replace("<!-- INSERT WARNING -->", warning)
       .replace("<!-- INSERT TITLE -->", getPageTitle(req, config))
-      .replace("<!-- INSERT META -->", getPageMetadataHtmlSnippet(config))
+      .replace("<!-- INSERT META -->", getPageMetadataHtmlSnippet(req, config, staticBaseUrl))
       .replace("<!-- INSERT TITLE SUFFIX -->", getPageTitleSuffix(server.getGristConfig()))
       .replace("<!-- INSERT BASE -->", `<base href="${staticBaseUrl}">` + tagManagerSnippet)
       .replace("<!-- INSERT LOCALE -->", preloads)
@@ -284,25 +284,21 @@ function getPageTitle(req: express.Request, config: GristLoadConfig): string {
  *
  * Note: The string returned is escaped and safe to insert into HTML.
  */
-function getPageMetadataHtmlSnippet(config: GristLoadConfig): string {
+function getPageMetadataHtmlSnippet(req: express.Request, config: GristLoadConfig, staticBaseUrl: string): string {
   const metadataElements: string[] = [];
   const maybeDoc = getDocFromConfig(config);
 
-  const description = maybeDoc?.options?.description;
-  if (description) {
-    const content = handlebars.Utils.escapeExpression(description);
-    metadataElements.push(`<meta name="description" content="${content}">`);
-    metadataElements.push(`<meta property="og:description" content="${content}">`);
-    metadataElements.push(`<meta name="twitter:description" content="${content}">`);
-  }
+  const description = maybeDoc?.options?.description ?? String(translate(req, 'gristMetaDescription'));
+  const escapedDescription = handlebars.Utils.escapeExpression(description);
+  metadataElements.push(`<meta name="description" content="${escapedDescription}">`);
+  metadataElements.push(`<meta property="og:description" content="${escapedDescription}">`);
+  metadataElements.push(`<meta name="twitter:description" content="${escapedDescription}">`);
 
-  const icon = maybeDoc?.options?.icon;
-  if (icon) {
-    const content = handlebars.Utils.escapeExpression(icon);
-    metadataElements.push(`<meta name="thumbnail" content="${content}">`);
-    metadataElements.push(`<meta property="og:image" content="${content}">`);
-    metadataElements.push(`<meta name="twitter:image" content="${content}">`);
-  }
+  const icon = maybeDoc?.options?.icon ?? new URL('/img/logo-grist.png', staticBaseUrl).href;
+  const escapedIcon = handlebars.Utils.escapeExpression(icon);
+  metadataElements.push(`<meta name="thumbnail" content="${escapedIcon}">`);
+  metadataElements.push(`<meta property="og:image" content="${escapedIcon}">`);
+  metadataElements.push(`<meta name="twitter:image" content="${escapedIcon}">`);
 
   return metadataElements.join('\n');
 }

static/locales/en.server.json

@@ -1,6 +1,7 @@
 {
   "sendAppPage": {
-    "Loading": "Loading"
+    "Loading": "Loading",
+    "gristMetaDescription": "Grist is the evolution of spreadsheets."
   },
   "oidc": {
     "emailNotVerifiedError": "Please verify your email with the identity provider, and log in again."