chrome/renderer/resources/extensions/gcm_custom_bindings.js

// Copyright 2013 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Custom binding for the GCM API.

const forEach = require('utils').forEach;

apiBridge.registerCustomHook(function(bindingsAPI) {
  const apiFunctions = bindingsAPI.apiFunctions;
  const gcm = bindingsAPI.compiledApi;

  apiFunctions.setUpdateArgumentsPostValidate(
      'send', function(message, callback) {
        // Validate message.data.
        let payloadSize = 0;
        forEach(message.data, function(property, value) {
          if (property.length === 0) {
            throw new Error('One of data keys is empty.');
          }

          const lowerCasedProperty = property.toLowerCase();
          // Issue an error for forbidden prefixes of property names.
          if (lowerCasedProperty.startsWith('goog.') ||
              lowerCasedProperty.startsWith('google') ||
              property.startsWith('collapse_key')) {
            throw new Error('Invalid data key: ' + property);
          }

          payloadSize += property.length + value.length;
        });

        if (payloadSize > gcm.MAX_MESSAGE_SIZE) {
          throw new Error(
              'Payload exceeded allowed size limit. Payload size is: ' +
              payloadSize);
        }

        if (payloadSize === 0) {
          throw new Error('No data to send.');
        }

        return arguments;
      });
});