Initial CL for Downloads resumption.

content/browser/download/base_file.cc

 // Copyright (c) 2012 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 "content/browser/download/base_file.h"
 
 #include "base/bind.h"
 #include "base/file_util.h"
 #include "base/format_macros.h"
 #include "base/logging.h"
@@ skipping 278 matching lines @@
     // writing at the end of the file.
     int64 seek_result = file_stream_->SeekSync(net::FROM_END, 0);
     if (seek_result < 0) {
       ClearStream();
       return LogNetError("Seek", static_cast<net::Error>(seek_result));
     }
   } else {
     file_stream_->SetBoundNetLogSource(bound_net_log_);
   }
 
+  int64 file_size = file_stream_->SeekSync(net::FROM_END, 0);
+  if (file_size > bytes_so_far_) {
+    // The file is larger than we expected.
+    // This is OK, as long as we don't use the extra.
+    // Truncate the file.
+    int64 truncate_result = file_stream_->Truncate(bytes_so_far_);
+    if (truncate_result < 0)
+      return LogNetError("Truncate", static_cast<net::Error>(truncate_result));
+
+    // If if wasn't an error, it should have truncated to the size
+    // specified.
+    DCHECK_EQ(bytes_so_far_, truncate_result);
+  } else if (file_size < bytes_so_far_) {
+    // The file is shorter than we expected.  Our hashes won't be valid.
+    return LogInterruptReason("Unable to seek to last written point", 0,
+                              DOWNLOAD_INTERRUPT_REASON_FILE_TOO_SHORT);
+  }
+
   return DOWNLOAD_INTERRUPT_REASON_NONE;
 }
 
 void BaseFile::Close() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
 
   bound_net_log_.AddEvent(net::NetLog::TYPE_DOWNLOAD_FILE_CLOSED);
 
   if (file_stream_.get()) {
 #if defined(OS_CHROMEOS)
@@ skipping 42 matching lines @@
     const char* operation,
     int os_error,
     DownloadInterruptReason reason) {
   bound_net_log_.AddEvent(
       net::NetLog::TYPE_DOWNLOAD_FILE_ERROR,
       base::Bind(&FileInterruptedNetLogCallback, operation, os_error, reason));
   return reason;
 }
 
 }  // namespace content