Add AttachmentDownloader interface, change signature of AttachmentStore::Read

- AttachmentDownloader interface is similar to AttachmentUploader interface.
  No implementation yet.
- AttachmentStore::Read guarantee should be stronger. It should attempt
  to read all attachments and return list of attachment ids that can't
  be loaded locally. Those need to be downloaded from server.

R=maniscalco@chromium.org
BUG=376073

Review URL: https://codereview.chromium.org/293143002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@272585 0039d316-1c4b-4281-b951-d872f2087c98

6 files changed, 71 insertions, 12 deletions

diff --git a/sync/api/attachments/attachment_downloader.cc b/sync/api/attachments/attachment_downloader.cc
new file mode 100644
index 0000000..a0108f7
--- /dev/null
+++ b/sync/api/attachments/attachment_downloader.cc
@@ -0,0 +1,12 @@
+// 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.
+
+#include "sync/api/attachments/attachment_downloader.h"
+
+namespace syncer {
+
+AttachmentDownloader::~AttachmentDownloader() {
+}
+
+}  // namespace syncer
diff --git a/sync/api/attachments/attachment_downloader.h b/sync/api/attachments/attachment_downloader.h
new file mode 100644
index 0000000..0473899
--- /dev/null
+++ b/sync/api/attachments/attachment_downloader.h
@@ -0,0 +1,41 @@
+// 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 SYNC_API_ATTACHMENTS_ATTACHMENT_DOWNLOADER_H_
+#define SYNC_API_ATTACHMENTS_ATTACHMENT_DOWNLOADER_H_
+
+#include "base/callback.h"
+#include "base/memory/scoped_ptr.h"
+#include "sync/api/attachments/attachment.h"
+#include "sync/base/sync_export.h"
+
+namespace syncer {
+
+// AttachmentDownloader is responsible for downloading attachments from server.
+class SYNC_EXPORT AttachmentDownloader {
+ public:
+  // The result of a DownloadAttachment operation.
+  enum DownloadResult {
+    DOWNLOAD_SUCCESS,            // No error, attachment was downloaded
+                                 // successfully.
+    DOWNLOAD_UNSPECIFIED_ERROR,  // An unspecified error occurred.
+  };
+
+  typedef base::Callback<void(const DownloadResult&, scoped_ptr<Attachment>)>
+      DownloadCallback;
+
+  virtual ~AttachmentDownloader();
+
+  // Download attachment referred by |attachment_id| and invoke |callback| when
+  // done.
+  //
+  // |callback| will receive a DownloadResult code and an Attachment object. If
+  // DownloadResult is not DOWNLOAD_SUCCESS then attachment pointer is NULL.
+  virtual void DownloadAttachment(const AttachmentId& attachment_id,
+                                  const DownloadCallback& callback) = 0;
+};
+
+}  // namespace syncer
+
+#endif  // SYNC_API_ATTACHMENTS_ATTACHMENT_DOWNLOADER_H_
diff --git a/sync/api/attachments/attachment_service_impl.cc b/sync/api/attachments/attachment_service_impl.cc
index a77d052..af2dea7 100644
--- a/sync/api/attachments/attachment_service_impl.cc
+++ b/sync/api/attachments/attachment_service_impl.cc
@@ -95,9 +95,11 @@ void AttachmentServiceImpl::OnSyncDataUpdate(
   // attachments from local storage (bug 356351).
 }
 
-void AttachmentServiceImpl::ReadDone(const GetOrDownloadCallback& callback,
-                                     const AttachmentStore::Result& result,
-                                     scoped_ptr<AttachmentMap> attachments) {
+void AttachmentServiceImpl::ReadDone(
+    const GetOrDownloadCallback& callback,
+    const AttachmentStore::Result& result,
+    scoped_ptr<AttachmentMap> attachments,
+    scoped_ptr<AttachmentIdList> unavailable_attachment_ids) {
   AttachmentService::GetOrDownloadResult get_result =
       AttachmentService::GET_UNSPECIFIED_ERROR;
   if (result == AttachmentStore::SUCCESS) {
diff --git a/sync/api/attachments/attachment_service_impl.h b/sync/api/attachments/attachment_service_impl.h
index aa99110..dbb1b53 100644
--- a/sync/api/attachments/attachment_service_impl.h
+++ b/sync/api/attachments/attachment_service_impl.h
@@ -45,7 +45,8 @@ class SYNC_EXPORT AttachmentServiceImpl : public AttachmentService,
  private:
   void ReadDone(const GetOrDownloadCallback& callback,
                 const AttachmentStore::Result& result,
-                scoped_ptr<AttachmentMap> attachments);
+                scoped_ptr<AttachmentMap> attachments,
+                scoped_ptr<AttachmentIdList> unavailable_attachment_ids);
   void DropDone(const DropCallback& callback,
                 const AttachmentStore::Result& result);
   void WriteDone(const StoreCallback& callback,
diff --git a/sync/api/attachments/attachment_store.h b/sync/api/attachments/attachment_store.h
index d86cd1b..b8834e0 100644
--- a/sync/api/attachments/attachment_store.h
+++ b/sync/api/attachments/attachment_store.h
@@ -38,17 +38,21 @@ class SYNC_EXPORT AttachmentStore {
     UNSPECIFIED_ERROR,  // An unspecified error occurred for one or more items.
   };
 
-  typedef base::Callback<void(const Result&, scoped_ptr<AttachmentMap>)>
-      ReadCallback;
+  typedef base::Callback<void(const Result&,
+                              scoped_ptr<AttachmentMap>,
+                              scoped_ptr<AttachmentIdList>)> ReadCallback;
   typedef base::Callback<void(const Result&)> WriteCallback;
   typedef base::Callback<void(const Result&)> DropCallback;
 
   // Asynchronously reads the attachments identified by |ids|.
   //
-  // |callback| will be invoked when finished. If any of the attachments do not
-  // exist or could not be read, |callback|'s Result will be UNSPECIFIED_ERROR
-  // and |callback| may receive a partial result. That is, AttachmentMap may be
-  // empty or may contain the attachments that were read successfully.
+  // |callback| will be invoked when finished. AttachmentStore will attempt to
+  // read all attachments specified in ids. If any of the attachments do not
+  // exist or could not be read, |callback|'s Result will be UNSPECIFIED_ERROR.
+  // Callback's AttachmentMap will contain all attachments that were
+  // successfully read, AttachmentIdList will contain attachment ids of
+  // attachments that are unavailable in attachment store, these need to be
+  // downloaded from server.
   //
   // Reads on individual attachments are treated atomically; |callback| will not
   // read only part of an attachment.
diff --git a/sync/api/attachments/attachment_uploader.h b/sync/api/attachments/attachment_uploader.h
index 325a9e7..12fe1a3 100644
--- a/sync/api/attachments/attachment_uploader.h
+++ b/sync/api/attachments/attachment_uploader.h
@@ -8,7 +8,6 @@
 #include "base/basictypes.h"
 #include "base/callback.h"
 #include "base/memory/scoped_ptr.h"
-#include "base/memory/weak_ptr.h"
 #include "sync/api/attachments/attachment.h"
 #include "sync/base/sync_export.h"
 
@@ -36,7 +35,7 @@ class SYNC_EXPORT AttachmentUploader {
   // or otherwise).
   //
   // |callback| will receive an UploadResult code and an updated AttachmentId
-  // |containing the server address of the newly uploaded attachment.
+  // containing the server address of the newly uploaded attachment.
   virtual void UploadAttachment(const Attachment& attachment,
                                 const UploadCallback& callback) = 0;
 };