1 files changed, 138 insertions, 0 deletions
diff --git a/devtools/shared/worker/helper.js b/devtools/shared/worker/helper.js
new file mode 100644
index 0000000000..20ccd3de5e
--- /dev/null
+++ b/devtools/shared/worker/helper.js
@@ -0,0 +1,138 @@
+/* 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/. */
+
+/* eslint-env amd */
+
+"use strict";
+
+/* global workerHelper */
+/* exported workerHelper */
+(function (root, factory) {
+  if (typeof define === "function" && define.amd) {
+    define(factory);
+  } else if (typeof exports === "object") {
+    module.exports = factory();
+  } else {
+    root.workerHelper = factory();
+  }
+})(this, function () {
+  /**
+   * This file is to only be included by ChromeWorkers. This exposes
+   * a `createTask` function to workers to register tasks for communication
+   * back to `devtools/shared/worker`.
+   *
+   * Tasks can be send their responses via a return value, either a primitive
+   * or a promise.
+   *
+   * createTask(self, "average", function (data) {
+   *   return data.reduce((sum, val) => sum + val, 0) / data.length;
+   * });
+   *
+   * createTask(self, "average", function (data) {
+   *   return new Promise((resolve, reject) => {
+   *     resolve(data.reduce((sum, val) => sum + val, 0) / data.length);
+   *   });
+   * });
+   *
+   *
+   * Errors:
+   *
+   * Returning an Error value, or if the returned promise is rejected, this
+   * propagates to the DevToolsWorker as a rejected promise. If an error is
+   * thrown in a synchronous function, that error is also propagated.
+   */
+
+  /**
+   * Takes a worker's `self` object, a task name, and a function to
+   * be called when that task is called. The task is called with the
+   * passed in data as the first argument
+   *
+   * @param {object} self
+   * @param {string} name
+   * @param {function} fn
+   */
+  function createTask(self, name, fn) {
+    // Store a hash of task name to function on the Worker
+    if (!self._tasks) {
+      self._tasks = {};
+    }
+
+    // Create the onmessage handler if not yet created.
+    if (!self.onmessage) {
+      self.onmessage = createHandler(self);
+    }
+
+    // Store the task on the worker.
+    self._tasks[name] = fn;
+  }
+
+  /**
+   * Creates the `self.onmessage` handler for a Worker.
+   *
+   * @param {object} self
+   * @return {function}
+   */
+  function createHandler(self) {
+    return function (e) {
+      const { id, task, data } = e.data;
+      const taskFn = self._tasks[task];
+
+      if (!taskFn) {
+        self.postMessage({ id, error: `Task "${task}" not found in worker.` });
+        return;
+      }
+
+      try {
+        handleResponse(taskFn(data));
+      } catch (ex) {
+        handleError(ex);
+      }
+
+      function handleResponse(response) {
+        // If a promise
+        if (response && typeof response.then === "function") {
+          response.then(
+            val => self.postMessage({ id, response: val }),
+            handleError
+          );
+        } else if (response instanceof Error) {
+          // If an error object
+          handleError(response);
+        } else {
+          // If anything else
+          self.postMessage({ id, response });
+        }
+      }
+
+      function handleError(error = "Error") {
+        try {
+          // First, try and structured clone the error across directly.
+          self.postMessage({ id, error });
+        } catch (x) {
+          // We could not clone whatever error value was given. Do our best to
+          // stringify it.
+          let errorString = `Error while performing task "${task}": `;
+
+          try {
+            errorString += error.toString();
+          } catch (ex) {
+            errorString += "<could not stringify error>";
+          }
+
+          if ("stack" in error) {
+            try {
+              errorString += "\n" + error.stack;
+            } catch (err) {
+              // Do nothing
+            }
+          }
+
+          self.postMessage({ id, error: errorString });
+        }
+      }
+    };
+  }
+
+  return { createTask };
+});