Bug 1585410 - Fix race in ClientID.jsm r=janerik

If we opt out of Telemetry and then back into it, we might end up with
out-of-order writes and deletes to the clientid state file. This would result
in us sending pings with c0ffee canary client ids.

So let's wait for pending save tasks before we process our removal task.

Also, while I'm here, let's add some trace logging to client id operations.

Differential Revision: https://phabricator.services.mozilla.com/D51709

--HG--
extra : moz-landing-system : lando

toolkit/components/telemetry/app/ClientID.jsm

@@ -159,6 +159,7 @@ var ClientIDImpl = {
    * If no Client ID is found, we generate a new one.
    */
   async _doLoadClientID() {
+    this._log.trace(`_doLoadClientID`);
     // If there's a removal in progress, let's wait for it
     await this._removeClientIdTask;
 
@@ -169,6 +170,7 @@ var ClientIDImpl = {
         this._wasCanary = state.wasCanary;
       }
       if (state && this.updateClientID(state.clientID)) {
+        this._log.trace(`_doLoadClientID: Client id loaded from state.`);
         return this._clientID;
       }
     } catch (e) {
@@ -185,6 +187,7 @@ var ClientIDImpl = {
     // result in orphaning.
     await this._saveClientIdTask;
 
+    this._log.trace("_doLoadClientID: New client id loaded and persisted.");
     return this._clientID;
   },
 
@@ -194,6 +197,7 @@ var ClientIDImpl = {
    * @return {Promise} A promise resolved when the client ID is saved to disk.
    */
   async _saveClientID() {
+    this._log.trace(`_saveClientID`);
     let obj = { clientID: this._clientID };
     // We detected a canary client ID when resetting, storing this as a flag
     if (AppConstants.platform == "android" && this._wasCanary) {
@@ -291,6 +295,7 @@ var ClientIDImpl = {
   },
 
   async setClientID(id) {
+    this._log.trace("setClientID");
     if (!this.updateClientID(id)) {
       throw new Error("Invalid client ID: " + id);
     }
@@ -301,6 +306,8 @@ var ClientIDImpl = {
   },
 
   async _doRemoveClientID() {
+    this._log.trace("_doRemoveClientID");
+
     // Reset stored id.
     this._clientID = null;
     this._clientIDHash = null;
@@ -308,11 +315,15 @@ var ClientIDImpl = {
     // Clear the client id from the preference cache.
     Services.prefs.clearUserPref(PREF_CACHED_CLIENTID);
 
+    // If there is a save in progress, wait for it to complete.
+    await this._saveClientIdTask;
+
     // Remove the client id from disk
     await OS.File.remove(gStateFilePath, { ignoreAbsent: true });
   },
 
   async resetClientID() {
+    this._log.trace("resetClientID");
     let oldClientId = this._clientID;
 
     // Wait for the removal.