Bug 1597358 - Create a backup of logins.json to use when logins.json is missing or corrupt. r=MattN

Depends on D78477

Differential Revision: https://phabricator.services.mozilla.com/D79688

modules/libpref/init/all.js

@@ -3748,6 +3748,7 @@ pref("signon.autologin.proxy",              false);
 pref("signon.capture.inputChanges.enabled", true);
 pref("signon.formlessCapture.enabled",      true);
 pref("signon.generation.available",               true);
+pref("signon.backup.enabled",               false);
 // A value of "-1" disables new-password heuristics. Can be updated once Bug 1618058 is resolved.
 pref("signon.generation.confidenceThreshold",     "-1");
 pref("signon.generation.enabled",                 true);

toolkit/components/passwordmgr/LoginStore.jsm

@@ -77,10 +77,11 @@ const MAX_DATE_MS = 8640000000000000;
  * @param aPath
  *        String containing the file path where data should be saved.
  */
-function LoginStore(aPath) {
+function LoginStore(aPath, aBackupPath = "") {
   JSONFile.call(this, {
     path: aPath,
     dataPostProcessor: this._dataPostProcessor.bind(this),
+    backupTo: aBackupPath,
   });
 }
 

toolkit/components/passwordmgr/storage-json.js

@@ -89,7 +89,17 @@ class LoginManagerStorage_json {
 
       // Set the reference to LoginStore synchronously.
       let jsonPath = OS.Path.join(OS.Constants.Path.profileDir, "logins.json");
-      this._store = new LoginStore(jsonPath);
+      let backupPath = "";
+      let loginsBackupEnabled = Services.prefs.getBoolPref(
+        "signon.backup.enabled"
+      );
+      if (loginsBackupEnabled) {
+        backupPath = OS.Path.join(
+          OS.Constants.Path.profileDir,
+          "logins-backup.json"
+        );
+      }
+      this._store = new LoginStore(jsonPath, backupPath);
 
       return (async () => {
         // Load the data asynchronously.

toolkit/modules/JSONFile.jsm

@@ -109,6 +109,8 @@ const kSaveDelayMs = 1500;
  *                      testing.
  *        - compression: A compression algorithm to use when reading and
  *                       writing the data.
+ *        - backupTo: A boolean value indicating whether writeAtomic should create
+ *                    a backup before writing to json files.
  */
 function JSONFile(config) {
   this.path = config.path;
@@ -130,6 +132,10 @@ function JSONFile(config) {
     this._options.compression = config.compression;
   }
 
+  if (config.backupTo) {
+    this._options.backupTo = config.backupTo;
+  }
+
   this._finalizeAt = config.finalizeAt || AsyncShutdown.profileBeforeChange;
   this._finalizeInternalBound = this._finalizeInternal.bind(this);
   this._finalizeAt.addBlocker(