[Extensions Binding] Allow for registering custom hooks

extensions/renderer/api_binding_hooks.h

+// Copyright 2016 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.
+
+#ifndef EXTENSIONS_RENDERER_API_BINDING_HOOKS_H_
+#define EXTENSIONS_RENDERER_API_BINDING_HOOKS_H_
+
+#include <map>
+#include <memory>
+#include <string>
+
+#include "base/callback.h"
+#include "base/macros.h"
+#include "extensions/renderer/api_binding_types.h"
+#include "v8/include/v8.h"
+
+namespace gin {
+class Arguments;
+}
+
+namespace extensions {
+
+// A class to register custom hooks for given API calls that need different
+// handling. An instance exists for a single API, but can be used across
+// multiple contexts (but only on the same thread).
+// TODO(devlin): We have both C++ and JS custom bindings, but this only allows
+// for registration of C++ handlers. Add JS support.
+class APIBindingHooks {
+ public:
+  // The callback to handle an API method. We pass in the expected signature
+  // (so the caller can verify arguments, optionally after modifying/"massaging"
+  // them) and the passed arguments. The handler is responsible for returning,
+  // which depending on the API could mean either returning synchronously
+  // through gin::Arguments::Return or asynchronously through a passed callback.
+  // TODO(devlin): As we continue expanding the hooks interface, we should allow
+  // handlers to register a request so that they don't have to maintain a
+  // reference to the callback themselves.
+  using HandleRequestHook =
+      base::Callback<void(const binding::APISignature*, gin::Arguments*)>;
+
+  APIBindingHooks();
+  ~APIBindingHooks();
+
+  // Register a custom binding to handle requests.
+  void RegisterHandleRequest(const std::string& method_name,
+                             const HandleRequestHook& hook);
+
+  // Returns the custom hook for the given method, or a null callback if none
+  // exists.
+  HandleRequestHook GetHandleRequest(const std::string& method_name);
+
+ private:
+  // Whether we've tried to use any hooks associated with this object.
+  bool hooks_used_ = false;
+
+  // All registered request handlers.
+  std::map<std::string, HandleRequestHook> request_hooks_;
+
+  DISALLOW_COPY_AND_ASSIGN(APIBindingHooks);
+};
+
+}  // namespace extensions
+
+#endif  // EXTENSIONS_RENDERER_API_BINDING_HOOKS_H_