Initial PlzNavigate RDH-side logic.

content/browser/loader/navigation_url_loader.h

+// Copyright 2014 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_NAVIGATION_URL_LOADER_H_
+#define CONTENT_BROWSER_LOADER_NAVIGATION_URL_LOADER_H_
+
+#include "base/basictypes.h"
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "content/common/content_export.h"
+
+namespace net {
+struct RedirectInfo;
+}
+
+namespace content {
+
+class BrowserContext;
+class NavigationURLLoaderFactory;
+class StreamHandle;
+class ResourceRequestBody;
+struct NavigationRequestInfo;
+struct ResourceResponse;
+
+// PlzNavigate: The navigation logic's UI thread entry point into the resource
+// loading stack. It exposes an interface to control the request prior to
+// receiving the response. If the NavigationURLLoader is destroyed before
+// OnResponseStarted is called, the request is aborted.
+class CONTENT_EXPORT NavigationURLLoader {
+ public:
+  class Delegate {
+   public:
+    virtual ~Delegate() {}
+
+    // Called when the request is redirected. Call FollowRedirect to continue

[nasko, 2014/09/24 21:15:34]

What happens if FollowRedirect is not called? What is the Delegate supposed to
do if it wants to cancel the request?

[davidben, 2014/10/03 16:27:52]

If FollowRedirect isn't called, the request just sits there paused. To cancel
the request, destroy the loader. (Can also add an explicit Cancel method if
that's preferable. Seemed we're going to be holding on to a scoped_ptr anyway,
so we can just trash the loader.)

+    // processing the request. Apart from the reference count on |response|,
+    // they must not be modified on the UI thread.

[nasko, 2014/09/24 21:15:34]

nit: What is "they"?

[davidben, 2014/10/03 16:27:52]

Removed the comment. It makes a copy of the ResourceResponse now (which we'll be
able to elide with https://crbug.com/416050).

+    virtual void OnRequestRedirected(const net::RedirectInfo& redirect_info,
+                                     ResourceResponse* response) = 0;
+
+    // Called when the request receives its response. No further calls will be
+    // made to the delegate. The response body is returned as a stream in
+    // |body|.
+    virtual void OnResponseStarted(ResourceResponse* response,
+                                   scoped_ptr<StreamHandle> body) = 0;
+

[nasko, 2014/09/24 21:15:34]

Do we need to notify the delegate if the request resulted in a download? Or is
it magically handled behind the scenes somehow?

[davidben, 2014/10/03 16:27:52]

If it results in a download, we'll get OnRequestFailed(ERR_ABORTED), so we'll
need to treat that error code special as we do now. (Don't show an error page.)

After all this, I'd actually like to move that out of the loader and into the
navigation logic. So something like...

func OnResponseStarted(response, body) {
    if ShouldDownload(response) {
       DoDownloadThing(response, body)
    } else if ShouldInterceptAsStream(response) {
       DoStreamThing(response, body)
    } else if response.mime_type == "application/x-x509-user-cert" {
       DoUserCertThing(response, body)
    } else {
       // Web content
       rfh := PickAppropriateRenderer(response)
       rfh.CommitNavigation(response, body)
    }
}

(I.e. all these download-like mechanisms don't intercept a request but they're
just part of the dispatch logic in deciding what to do with the load. Except,
you know, looking very different and not in a suspiciously Go-ish psuedocode.)

+    // Called if the request fails before receving a response. |net_error| is a
+    // network error code for the failure.
+    virtual void OnRequestFailed(int net_error) = 0;

[mmenke, 2014/09/23 17:22:45]

 private:
  DISALLOW_COPY_AND_ASSIGN?

Suppose it's not really needed for abstract classes, but seems simplest to just
always include it.

[davidben, 2014/10/03 16:27:52]

Done, but it requires adding a default ctor somewhere.

+  };
+
+  // Creates a NavigationURLLoader. The caller is responsible for ensuring that
+  // |delegate| outlives the loader. |request_body| must not be accessed on the
+  // UI thread after this point.
+  //
+  // TODO(davidben): When navigation is disentangled from the loader, the
+  // request parameters should not come in as a navigation-specific
+  // structure. Information like has_user_gesture and
+  // should_replace_current_entry shouldn't be needed at this layer.
+  static NavigationURLLoader* Create(BrowserContext* browser_context,
+                                     int64 frame_tree_node_id,
+                                     const NavigationRequestInfo& request_info,
+                                     ResourceRequestBody* request_body,
+                                     Delegate* delegate);
+
+  // For testing purposes; sets the factory for use in testing.
+  static void SetFactoryForTesting(NavigationURLLoaderFactory* factory);
+
+  virtual ~NavigationURLLoader() {}
+
+  // Called in response to OnRequestRedirected to continue processing the
+  // request.
+  virtual void FollowRedirect() = 0;

[mmenke, 2014/09/23 17:22:45]

 private:
  DISALLOW_COPY_AND_ASSIGN?

[davidben, 2014/10/03 16:27:52]

Done, but it requires adding a default ctor somewhere.

+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_LOADER_NAVIGATION_URL_LOADER_H_