[Offline] Adding archiver interface

components/offline_pages/offline_page_archiver.h

+// Copyright 2015 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 COMPONENTS_OFFLINE_PAGES_OFFLINE_PAGE_ARCHIVER_H_
+#define COMPONENTS_OFFLINE_PAGES_OFFLINE_PAGE_ARCHIVER_H_
+
+#include "base/files/file_path.h"
+#include "url/gurl.h"
+
+namespace offline_pages {
+
+// Interface of a class responsible for creation of the archive for offline use.
+//
+// Archiver will be implemented by embedder and may have additional methods that
+// are not interesting from the perspective of OfflinePageModel. Example of such
+// extra information or capability is a way to enumerate available WebContents
+// to find the one that needs to be used to create archive (or to map it to the
+// URL passed in CreateArchive in some other way).
+//
+// Archiver will be responsible for naming the file that is being saved (it has
+// URL, title and the whole page content at its disposal). For that it should be
+// also configured with the path where the archives are stored.
+//
+// Archiver should be able to archive multiple pages in parallel, as these are
+// asynchronous calls carried out by some other component.
+//
+// If archiver gets two consecutive requests to archive the same page (may be
+// run in parallel) it can generate 2 different names for files and save the
+// same page separately, as if these were 2 completely unrelated pages. It is up
+// to the caller (e.g. OfflinePageModel) to make sure that situation like that
+// does not happen.
+//
+// If the page is not completely loaded, it is up to the implementation of the
+// archiver whether to respond with ERROR_CONTENT_UNAVAILBLE, wait longer to
+// actually snapshot a complete page, or snapshot whatever is available at that
+// point in time (what the user sees).
+//
+// TODO(fgorski): Add ability to delete archive.
+// TODO(fgorski): Add ability to check that archive exists.
+// TODO(fgorski): Add ability to refresh an existing archive in one step.
+// TODO(fgorski): Add ability to identify all of the archives in the directory,
+// to enable to model to reconcile the archives.
+class OfflinePageArchiver {
+ public:
+  // Represents an in progress request to archive a page.
+  class Request {
+   public:
+    virtual ~Request() {}
+
+    // Cancels an in progress request to archive a page.
+    virtual void Cancel() = 0;
+    virtual const GURL& url() const = 0;
+  };
+
+  // Errors that will be reported when archive creation fails.
+  enum ArchiverResult {
+    SUCCESSFULLY_CREATED,       // Archive created successfully.
+    ERROR_UNKNOWN,              // Don't know what went wrong.
+    ERROR_DEVICE_FULL,          // Cannot save the archive - device is full.
+    ERROR_CANCELLED,            // Caller cancelled the request.
+    ERROR_CONTENT_UNAVAILABLE,  // Content to archive is not available.
+  };
+
+  // Interface of the clients that requests to archive pages.
+  class Client {
+   public:
+    virtual ~Client() {}
+
+    // Callback called by the archiver when archiver creation is complete.
+    // |result| will indicate SUCCESSFULLY_CREATED upon success, or a specific
+    // error, when it failed.
+    virtual void OnCreateArchiveDone(Request* request,
+                                     ArchiverResult result,
+                                     const base::FilePath& file_path) = 0;
+  };
+
+  virtual ~OfflinePageArchiver() {}
+
+  // Starts creating the archive. Will pass result by calling methods on the
+  // passed in client. Caller owns the returned request object.
+  // If request is deleted during the archiving, the callback will not be
+  // invoked. The archive might however be created.
+  virtual scoped_ptr<Request> CreateArchive(const GURL& url,
+                                            Client* client) = 0;
+};
+
+}  // namespace offline_pages
+
+#endif  // COMPONENTS_OFFLINE_PAGES_OFFLINE_PAGE_ARCHIVER_H_