Add custom bindings for chrome.printerProvider API

The bindings are used to implement callbacks for the API events.
The event arguments as sent from C++ are massaged before dispatching them
the event listener to remove the requestId argument provided by
printerProvider implementation and add a callback that calls
chrome.printerProviderInternal API function (with requestId and the value
provided by the extension). The internal API is supposed to handle the
callback (still to be implemented).

BUG=408772
TEST=None (will be added in subsequent cls, with the C++ side API
implementations)

Review URL: https://codereview.chromium.org/845403008

Cr-Commit-Position: refs/heads/master@{#312022}

1 files changed, 83 insertions, 0 deletions

diff --git a/extensions/renderer/resources/printer_provider_custom_bindings.js b/extensions/renderer/resources/printer_provider_custom_bindings.js
new file mode 100644
index 0000000..9bf9fa2
--- /dev/null
+++ b/extensions/renderer/resources/printer_provider_custom_bindings.js
@@ -0,0 +1,83 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+var binding = require('binding').Binding.create('printerProvider');
+var printerProviderInternal = require('binding').Binding.create(
+    'printerProviderInternal').generate();
+var eventBindings = require('event_bindings');
+
+var printerProviderSchema =
+    requireNative('schema_registry').GetSchema('printerProvider')
+var utils = require('utils');
+var validate = require('schemaUtils').validate;
+
+// Custom bindings for chrome.printerProvider API.
+// The bindings are used to implement callbacks for the API events. Internally
+// each event is passed requestId argument used to identify the callback
+// associated with the event. This argument is massaged out from the event
+// arguments before dispatching the event to consumers. A callback is appended
+// to the event arguments. The callback wraps an appropriate
+// chrome.printerProviderInternal API function that is used to report the event
+// result from the extension. The function is passed requestId and values
+// provided by the extension. It validates that the values provided by the
+// extension match chrome.printerProvider event callback schemas. It also
+// ensures that a callback is run at most once. In case there is an exception
+// during event dispatching, the chrome.printerProviderInternal function
+// is called with a default error value.
+//
+
+// Handles a chrome.printerProvider event as described in the file comment.
+// |eventName|: The event name.
+// |resultreporter|: The function that should be called to report event result.
+//                   One of chrome.printerProviderInternal API functions.
+function handleEvent(eventName, resultReporter) {
+  eventBindings.registerArgumentMassager(
+      'printerProvider.' + eventName,
+      function(args, dispatch) {
+        var responded = false;
+
+        // Validates that the result passed by the extension to the event
+        // callback matches the callback schema. Throws an exception in case of
+        // an error.
+        var validateResult = function(result) {
+          var eventSchema =
+              utils.lookup(printerProviderSchema.events, 'name', eventName);
+          var callbackSchema =
+              utils.lookup(eventSchema.parameters, 'type', 'function');
+
+          validate([result], callbackSchema.parameters);
+        };
+
+        // Function provided to the extension as the event callback argument.
+        // It makes sure that the event result hasn't previously been returned
+        // and that the provided result matches the callback schema. In case of
+        // an error it throws an exception.
+        var reportResult = function(result) {
+          if (responded) {
+            throw new Error(
+                'Event callback must not be called more than once.');
+          }
+
+          var finalResult = null;
+          try {
+            validateResult(result);  // throws on failure
+            finalResult = result;
+          } finally {
+            responded = true;
+            resultReporter(args[0] /* requestId */, finalResult);
+          }
+        };
+
+        dispatch(args.slice(1).concat(reportResult));
+      });
+}
+
+handleEvent('onGetPrintersRequested', printerProviderInternal.reportPrinters);
+
+handleEvent('onGetCapabilityRequested',
+            printerProviderInternal.reportPrinterCapability);
+
+handleEvent('onPrintRequested', printerProviderInternal.reportPrintResult);
+
+exports.binding = binding.generate();