Differential updates for components.

chrome/browser/component_updater/component_patcher.h

+// Copyright (c) 2013 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 CHROME_BROWSER_COMPONENT_UPDATER_COMPONENT_PATCHER_H_
+#define CHROME_BROWSER_COMPONENT_UPDATER_COMPONENT_PATCHER_H_
+
+#include "base/basictypes.h"
+#include "base/compiler_specific.h"
+#include "chrome/browser/component_updater/component_unpacker.h"
+
+namespace base {
+class FilePath;
+}
+
+class ComponentInstaller;
+
+// The type of a patch file.
+enum PatchType {

[erikwright (departed), 2013/06/17 17:24:28]

This enum in the global namespace seems dangerous and collision prone.

I'd recommend making it a class member (maybe it belongs in ComponentPatcher?).

Furthermore, I would consider whether a component_updater namespace should be
used for everything in this directory. Or at least the non-component-specific
bits.

[Sorin Jianu, 2013/06/17 22:21:09]

Done. We will introduce a namespace in a future CL.

+  kPatchTypeUnknown,
+  kPatchTypeCourgette,
+  kPatchTypeBsdiff,

[sra1, 2013/06/15 00:56:17]

One thing to consider:

Since Courgette ends with doing BSDiff(old+predicted,new), another way to get
BSDiff is to pass through to Courgette a list or other indication of formats it
is allowed to recognize.  If the list is empty, 'predicted' will be empty
(generated by a bsdiff between two empty sequences).

The overhead will be the Courgette header and a couple of additional BSDiff
headers, i.e. about 100 bytes.

[waffles, 2013/06/17 23:51:07]

That makes sense; but I think we prefer to keep it this way, at least for now;
being able to fall back on bsdiff without invoking courgette codepaths might be
useful for reliability reasons, and the smaller header is a bonus. Since we have
the --genbsdiff flag already, I think it makes sense to use it.

+};
+
+// Applies a delta patch to a file. Specifically, creates a file at

[robertshield, 2013/06/17 17:47:00]

From reading the implementation, it looks like a delta patch is a bundle that
includes a commands.json file that describes the operation to be performed. It
would be great to have a somewhat longer overview comment describing at a high
level how this stuff works.

[waffles, 2013/06/17 23:51:07]

Done; the comment for DifferentialUpdatePatch has been improved.

+// |output_file| using |input_file| patched according to the algorithm
+// specified by |patch_type| using |patch_file|. Sets the value of error to
+// the error code of the failing patch operation, if there is such a failure.
+class ComponentPatcher {
+ public:
+  ComponentPatcher() {}
+  virtual ComponentUnpacker::Error Patch(PatchType patch_type,
+                                         const base::FilePath& input_file,
+                                         const base::FilePath& patch_file,
+                                         const base::FilePath& output_file,
+                                         int* error) = 0;
+  virtual ~ComponentPatcher() {}
+};
+
+class ComponentPatcherCrossPlatform : public ComponentPatcher {
+ public:
+  ComponentPatcherCrossPlatform();
+  virtual ComponentUnpacker::Error Patch(PatchType patch_type,
+                                         const base::FilePath& input_file,
+                                         const base::FilePath& patch_file,
+                                         const base::FilePath& output_file,
+                                         int* error) OVERRIDE;
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ComponentPatcherCrossPlatform);
+};
+
+// Recreates the content of a full CRX by taking the unpacked files of a
+// differential component update in |input_dir| and patching the installed
+// component files.
+// The resulting files are written into the |unpack_dir| directory.
+ComponentUnpacker::Error DifferentialUpdatePatch(
+    const base::FilePath& input_dir,
+    const base::FilePath& unpack_dir,
+    ComponentPatcher* component_patcher,
+    ComponentInstaller* installer,
+    int* error);
+
+#endif  // CHROME_BROWSER_COMPONENT_UPDATER_COMPONENT_PATCHER_H_