1 files changed, 132 insertions, 0 deletions
diff --git a/toolkit/components/normandy/lib/PrefUtils.sys.mjs b/toolkit/components/normandy/lib/PrefUtils.sys.mjs
new file mode 100644
index 0000000000..445744d88f
--- /dev/null
+++ b/toolkit/components/normandy/lib/PrefUtils.sys.mjs
@@ -0,0 +1,132 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * 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";
+
+const lazy = {};
+ChromeUtils.defineESModuleGetters(lazy, {
+  LogManager: "resource://normandy/lib/LogManager.sys.mjs",
+});
+
+XPCOMUtils.defineLazyGetter(lazy, "log", () => {
+  return lazy.LogManager.getLogger("preference-experiments");
+});
+
+const kPrefBranches = {
+  user: Services.prefs,
+  default: Services.prefs.getDefaultBranch(""),
+};
+
+export var PrefUtils = {
+  /**
+   * Get a preference of any type from the named branch.
+   * @param {string} pref
+   * @param {object} [options]
+   * @param {"default"|"user"} [options.branchName="user"] One of "default" or "user"
+   * @param {string|boolean|integer|null} [options.defaultValue]
+   *   The value to return if the preference does not exist. Defaults to null.
+   */
+  getPref(pref, { branch = "user", defaultValue = null } = {}) {
+    const branchObj = kPrefBranches[branch];
+    if (!branchObj) {
+      throw new this.UnexpectedPreferenceBranch(
+        `"${branch}" is not a valid preference branch`
+      );
+    }
+    const type = branchObj.getPrefType(pref);
+
+    try {
+      switch (type) {
+        case Services.prefs.PREF_BOOL: {
+          return branchObj.getBoolPref(pref);
+        }
+        case Services.prefs.PREF_STRING: {
+          return branchObj.getStringPref(pref);
+        }
+        case Services.prefs.PREF_INT: {
+          return branchObj.getIntPref(pref);
+        }
+        case Services.prefs.PREF_INVALID: {
+          return defaultValue;
+        }
+      }
+    } catch (e) {
+      if (branch === "default" && e.result === Cr.NS_ERROR_UNEXPECTED) {
+        // There is a value for the pref on the user branch but not on the default branch. This is ok.
+        return defaultValue;
+      }
+      // Unexpected error, re-throw it
+      throw e;
+    }
+
+    // If `type` isn't any of the above, throw an error. Don't do this in a
+    // default branch of switch so that error handling is easier.
+    throw new TypeError(`Unknown preference type (${type}) for ${pref}.`);
+  },
+
+  /**
+   * Set a preference on the named branch
+   * @param {string} pref
+   * @param {string|boolean|integer|null} value The value to set.
+   * @param {object} options
+   * @param {"user"|"default"} options.branchName The branch to make the change on.
+   */
+  setPref(pref, value, { branch = "user" } = {}) {
+    if (value === null) {
+      this.clearPref(pref, { branch });
+      return;
+    }
+    const branchObj = kPrefBranches[branch];
+    if (!branchObj) {
+      throw new this.UnexpectedPreferenceBranch(
+        `"${branch}" is not a valid preference branch`
+      );
+    }
+    switch (typeof value) {
+      case "boolean": {
+        branchObj.setBoolPref(pref, value);
+        break;
+      }
+      case "string": {
+        branchObj.setStringPref(pref, value);
+        break;
+      }
+      case "number": {
+        branchObj.setIntPref(pref, value);
+        break;
+      }
+      default: {
+        throw new TypeError(
+          `Unexpected value type (${typeof value}) for ${pref}.`
+        );
+      }
+    }
+  },
+
+  /**
+   * Remove a preference from a branch. Note that default branch preferences
+   * cannot effectively be cleared. If "default" is passed for a branch, an
+   * error will be logged and nothing else will happen.
+   *
+   * @param {string} pref
+   * @param {object} options
+   * @param {"user"|"default"} options.branchName The branch to clear
+   */
+  clearPref(pref, { branch = "user" } = {}) {
+    if (branch === "user") {
+      kPrefBranches.user.clearUserPref(pref);
+    } else if (branch === "default") {
+      lazy.log.warn(
+        `Cannot reset pref ${pref} on the default branch. Pref will be cleared at next restart.`
+      );
+    } else {
+      throw new this.UnexpectedPreferenceBranch(
+        `"${branch}" is not a valid preference branch`
+      );
+    }
+  },
+
+  UnexpectedPreferenceType: class extends Error {},
+  UnexpectedPreferenceBranch: class extends Error {},
+};