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 CONTENT_EXPORT 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.
+  // Some implementation notes:
+  // 1) The returned pointer needs to be valid only until a single
+  // CreateLoaderAndStart call is made, and it is okay to do CHECK(false) for
+  // any subsequent calls.
+  // 2) 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 need to
+  // 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.)
+  virtual void MaybeCreateLoaderFactory(const ResourceRequest& resource_request,
+                                        ResourceContext* resource_context,
+                                        LoaderFactoryCallback callback) = 0;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_LOADER_URL_LOADER_REQUEST_HANDLER_H_