Fix unnecessary link preview fetches.

js/link_previews_helper.js

@@ -13,6 +13,9 @@
   window.Signal = window.Signal || {};
   window.Signal.LinkPreviews = window.Signal.LinkPreviews || {};
 
+  // A cache mapping url to fetched previews
+  const previewCache = {};
+
   async function makeChunkedRequest(url) {
     const PARALLELISM = 3;
     const size = await textsecure.messaging.getProxiedSize(url);
@@ -68,7 +71,21 @@
     return StringView.arrayBufferToHex(digest);
   }
 
-  async function getPreview(url) {
+  // Wrapper function which utilizes cache
+  async function getPreview(url, skipCache = false) {
+    // If we have a request cached then use that
+    if (!skipCache && url in previewCache) {
+      return previewCache[url];
+    }
+
+    // Start the request
+    const promise = _getPreview(url);
+    previewCache[url] = promise;
+
+    return promise;
+  }
+
+  async function _getPreview(url) {
     let html;
     try {
       html = await textsecure.messaging.makeProxiedRequest(url);

ts/components/JazzIcon/JazzIcon.tsx

@@ -94,7 +94,11 @@ export class JazzIcon extends React.PureComponent<Props> {
   private hueShift(colors: Array<string>, generator: RNG) {
     const amount = generator.random() * 30 - wobble / 2;
 
-    return colors.map(hex => Color(hex).rotate(amount).hex());
+    return colors.map(hex =>
+      Color(hex)
+        .rotate(amount)
+        .hex()
+    );
   }
 
   private genShape(