make encrypted content fast load if already stored decrypted

ts/hooks/useEncryptedFileFetch.ts

@@ -1,12 +1,15 @@
 import { useEffect, useRef, useState } from 'react';
 
-import { getDecryptedMediaUrl } from '../session/crypto/DecryptedAttachmentsManager';
+import {
+  getAlreadyDecryptedMediaUrl,
+  getDecryptedMediaUrl,
+} from '../session/crypto/DecryptedAttachmentsManager';
 import { perfEnd, perfStart } from '../session/utils/Performance';
 
 export const useEncryptedFileFetch = (url: string, contentType: string) => {
   // tslint:disable-next-line: no-bitwise
   const [urlToLoad, setUrlToLoad] = useState('');
-  const [loading, setLoading] = useState(true);
+  const [loading, setLoading] = useState(false);
 
   const mountedRef = useRef(true);
 
@@ -22,8 +25,12 @@ export const useEncryptedFileFetch = (url: string, contentType: string) => {
       setLoading(false);
     }
   }
+  const alreadyDecrypted = getAlreadyDecryptedMediaUrl(url);
 
   useEffect(() => {
+    if (alreadyDecrypted) {
+      return;
+    }
     setLoading(true);
     mountedRef.current = true;
     void fetchUrl();
@@ -32,5 +39,9 @@ export const useEncryptedFileFetch = (url: string, contentType: string) => {
       mountedRef.current = false;
     };
   }, [url]);
+
+  if (alreadyDecrypted) {
+    return { urlToLoad: alreadyDecrypted, loading: false };
+  }
   return { urlToLoad, loading };
 };

ts/session/crypto/DecryptedAttachmentsManager.ts

@@ -105,3 +105,25 @@ export const getDecryptedMediaUrl = async (url: string, contentType: string): Pr
     return url;
   }
 };
+
+/**
+ *
+ * Returns the already decrypted URL or null
+ */
+export const getAlreadyDecryptedMediaUrl = (url: string): string | null => {
+  if (!url) {
+    return null;
+  }
+  if (url.startsWith('blob:')) {
+    return url;
+  } else if (
+    window.Signal.Migrations.attachmentsPath &&
+    url.startsWith(window.Signal.Migrations.attachmentsPath)
+  ) {
+    if (urlToDecryptedBlobMap.has(url)) {
+      const existingObjUrl = urlToDecryptedBlobMap.get(url)?.decrypted as string;
+      return existingObjUrl;
+    }
+  }
+  return null;
+};