[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:
+  using HandleRequestHook =

[jbroman, 2016/12/09 15:53:08]

Since I was confused, it might be helpful to describe exactly what the callback
is expected to do to handle the request. I gather it's expected to take
arguments from the gin::Arguments and then call gin::Arguments::Return? If so,
does that imply that the C++ ones are synchronous? Or if they are asynchronous,
how does that work?

[Devlin, 2016/12/09 16:35:06]

Unfortunately, there isn't a full standard for this.  Some APIs are synchronous,
in which case they could use gin::Arguments::Return.  Others allow for
asynchronocity (pass in a callback), but actually execute synchronously.  I've
added a comment that tries to shed a bit of light here, but unfortunately,
there's isn't necessarily a standard case. I've also added a TODO to make sure
that we have a way for handlers to register a request so that the bindings
system handles the callback lifetime maintenance, rather than the handler
holding onto a reference directly.

+      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:
+  // 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_