Bug 1828392 - [remote] Fix Log helpers isTrace/DebugLevelOrAbove r=webdriver-reviewers,whimboo

Differential Revision: https://phabricator.services.mozilla.com/D175606

remote/marionette/actors/MarionetteEventsChild.sys.mjs

@@ -26,7 +26,7 @@ export class MarionetteEventsChild extends JSWindowActorChild {
     // Prevent the logger from being created if the current log level
     // isn't set to 'trace'. This is important for a faster content process
     // creation when Marionette is running.
-    if (lazy.Log.isTraceLevelOrAbove) {
+    if (lazy.Log.isTraceLevelOrOrMore) {
       lazy.logger.trace(
         `[${this.browsingContext.id}] MarionetteEvents actor created ` +
           `for window id ${this.innerWindowId}`

remote/shared/Log.sys.mjs

@@ -2,10 +2,21 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs";
+
 import { Log as StdLog } from "resource://gre/modules/Log.sys.mjs";
 
 const PREF_REMOTE_LOG_LEVEL = "remote.log.level";
 
+const lazy = {};
+
+// Lazy getter which returns a cached value of the remote log level. Should be
+// used for static getters used to guard hot paths for logging, eg
+// isTraceLevelOrMore.
+XPCOMUtils.defineLazyGetter(lazy, "logLevel", () =>
+  Services.prefs.getCharPref(PREF_REMOTE_LOG_LEVEL, StdLog.Level.Fatal)
+);
+
 /** E10s compatible wrapper for the standard logger from Log.sys.mjs. */
 export class Log {
   static TYPES = {
@@ -38,10 +49,9 @@ export class Log {
    * above that. This should be used to guard logger.debug calls and avoid
    * instanciating logger instances unnecessarily.
    */
-  static get isDebugLevelOrAbove() {
-    return [StdLog.Level.All, StdLog.Level.Trace, StdLog.Level.Debug].includes(
-      PREF_REMOTE_LOG_LEVEL
-    );
+  static get isDebugLevelOrMore() {
+    // Debug is assigned 20, more verbose log levels have lower values.
+    return StdLog.Level[lazy.logLevel] <= StdLog.Level.Debug;
   }
 
   /**
@@ -49,10 +59,9 @@ export class Log {
    * above that. This should be used to guard logger.trace calls and avoid
    * instanciating logger instances unnecessarily.
    */
-  static get isTraceLevelOrAbove() {
-    return [StdLog.Level.All, StdLog.Level.Trace].includes(
-      PREF_REMOTE_LOG_LEVEL
-    );
+  static get isTraceLevelOrMore() {
+    // Trace is assigned 10, more verbose log levels have lower values.
+    return StdLog.Level[lazy.logLevel] <= StdLog.Level.Trace;
   }
 
   static get verbose() {

remote/shared/WebSocketConnection.sys.mjs

@@ -39,7 +39,7 @@ export class WebSocketConnection {
   }
 
   _log(direction, data) {
-    if (lazy.Log.isDebugLevelOrAbove) {
+    if (lazy.Log.isDebugLevelOrMore) {
       function replacer(key, value) {
         if (typeof value === "string") {
           return lazy.truncate`${value}`;