Truncate the download file name if it exceeds the filesystem limit.

base/file_util_win.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 "base/file_util.h"
 
 #include <windows.h>
 #include <psapi.h>
 #include <shellapi.h>
 #include <shlobj.h>
 #include <time.h>
 
+#include <algorithm>
 #include <limits>
 #include <string>
 
 #include "base/file_path.h"
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
 #include "base/process_util.h"
 #include "base/string_util.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/threading/thread_restrictions.h"
@@ skipping 920 matching lines @@
   bool success = false;
   HANDLE cp = GetCurrentProcess();
   if (::GetMappedFileNameW(cp, file_view, mapped_file_path, kMaxPathLength)) {
     *nt_path = FilePath(mapped_file_path);
     success = true;
   }
   ::UnmapViewOfFile(file_view);
   return success;
 }
 
+int GetMaximumPathComponentLength(const FilePath& path) {
+  base::ThreadRestrictions::AssertIOAllowed();
+
+  wchar_t volume_path[MAX_PATH];
+  if (!GetVolumePathNameW(path.NormalizePathSeparators().value().c_str(),
+                          volume_path,
+                          arraysize(volume_path))) {
+    return -1;
+  }
+
+  DWORD max_length = 0;
+  if (!GetVolumeInformationW(volume_path, NULL, 0, NULL, &max_length, NULL,
+                             NULL, 0)) {
+    return -1;
+  }
+
+  // Length of |path| with path separator appended.
+  size_t prefix = path.StripTrailingSeparators().value().size() + 1;
+  // The whole path string must be shorter than MAX_PATH. That is, it must be
+  // prefix + component_length < MAX_PATH (or equivalently, <= MAX_PATH - 1).
+  int whole_path_limit = std::max(0, MAX_PATH - 1 - static_cast<int>(prefix));
+  return std::min(whole_path_limit, static_cast<int>(max_length));
+}
+
 }  // namespace file_util