Network service: Implement URLLoader chaining for interceptors

content/browser/loader/url_loader_request_handler.h

+// Copyright 2017 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 CONTENT_BROWSER_LOADER_URL_LOADER_REQUEST_HANDLER_H_
+#define CONTENT_BROWSER_LOADER_URL_LOADER_REQUEST_HANDLER_H_
+
+#include "base/callback_forward.h"
+#include "base/macros.h"
+#include "content/common/url_loader_factory.mojom.h"
+
+namespace content {
+
+class ResourceContext;
+struct ResourceRequest;
+
+using LoaderFactoryCallback =
+    base::OnceCallback<void(mojom::URLLoaderFactory*)>;
+
+// An instance of this class is a per-request object and kept around during
+// the lifetime of a request (including multiple redirect legs) on IO thread.
+class URLLoaderRequestHandler {
+ public:
+  URLLoaderRequestHandler() = default;
+  virtual ~URLLoaderRequestHandler() = default;
+
+  // Calls |callback| with non-null factory if this handler can handle
+  // the request, calls it with nullptr otherwise.
+  // Note that the implementor is not supposed to set up and return
+  // URLLoaderFactory until it finds out that the handler is really going
+  // to handle the request. (For example ServiceWorker's request handler
+  // would not call the callback until it gets response from SW, and it
+  // may still call the callback with nullptr if it turns out that it needs
+  // to fallback to the network.)

[michaeln, 2017/05/26 17:42:27]

Can we specify that the returned URLLoaderFactory need only support a single
call to CreateLoaderAndStart(), so it would be valid for subsequent calls to
CreateLoaderAndStart() or any calls to the SyncLoad() to CHECK(false).

class OnceURLLoaderFactory would probably be overkill, but you get the idea

[kinuko, 2017/05/29 06:12:24]

Done.

+  virtual void MaybeCreateLoaderFactory(const ResourceRequest& resource_request,
+                                        ResourceContext* resource_context,
+                                        LoaderFactoryCallback callback) = 0;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_LOADER_URL_LOADER_REQUEST_HANDLER_H_