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

base/file_util_win.cc

Index: base/file_util_win.cc
diff --git a/base/file_util_win.cc b/base/file_util_win.cc
index 65fd6ebb43c3ff09bd82790678cfe2ac06ad50c7..42d8b5bbecbdd7c7735a2624ad1b700e5031b40f 100644
--- a/base/file_util_win.cc
+++ b/base/file_util_win.cc
@@ -8,8 +8,10 @@
 #include <psapi.h>
 #include <shellapi.h>
 #include <shlobj.h>
+#include <shlwapi.h>
 #include <time.h>
 
+#include <algorithm>
 #include <limits>
 #include <string>
 
@@ -948,4 +950,29 @@ bool NormalizeToNativeFilePath(const FilePath& path, FilePath* nt_path) {
   return success;
 }
 
+int GetMaximumPathComponentLength(const FilePath& path) {
+  base::ThreadRestrictions::AssertIOAllowed();
+  FilePath full_path(path);
+  if (!full_path.IsAbsolute() && !file_util::AbsolutePath(&full_path))
+    return -1;
+
+  // GetVolumeInformationW takes a root path ended with a backslash.
+  std::vector<FilePath::CharType> root(full_path.value().begin(),
+                                       full_path.value().end());
+  root.resize(root.size() + 2);  // +2 for trailing \0 and backslash.
+  PathStripToRootW(&root[0]);

[Mark Mentovai, 2013/02/14 13:40:58]

Looking at
http://msdn.microsoft.com/en-us/library/windows/desktop/bb773757(v=vs.85).aspx ,
it recommends PathCchStripToRoot because that function also has a size argument.

Looking at
http://msdn.microsoft.com/en-us/library/windows/desktop/hh707096(v=vs.85).aspx ,
I see that PathCchStripToRoot also works on UNC paths, and it says that
PathStripToRoot does not.

Do we care about UNC paths?

[asanka, 2013/02/14 16:06:53]

Unfortunately PathCchStripToRoot() appears to be only available on Windows 8 and
Windows Server 2012 and later.

Good point about the string size. The documentation for PathStripToRoot() states
that the buffer is expected to be of MAX_PATH length in characters and be NUL
terminated.

I think we should make sure that the buffer length requirements of
PathStripToRoot() be respected. I.e. make sure that the length of |path| doesn't
exceed MAX_PATH and size of |root| is MAX_PATH even if |path| is shorter than
MAX_PATH.

Also normalize path separators before calling this function
(FilePath::NormalizePathSeparators()). PathStripToRoot() doesn't seem to deal
with forward slashes even though some other Windows APIs do.
We do care about UNC paths. :-(

Have you looked at using GetVolumePathName() instead of Path{CCh,}StripToRoot()?

+  PathAddBackslashW(&root[0]);

[Mark Mentovai, 2013/02/14 13:40:58]

Same with PathCchAddBackslash. See
http://msdn.microsoft.com/en-us/library/windows/desktop/bb773561(v=vs.85).aspx
and
http://msdn.microsoft.com/en-us/library/windows/desktop/hh707078(v=vs.85).aspx .

+
+  DWORD max_length = 0;
+  if (!GetVolumeInformationW(&root[0], NULL, 0, NULL, &max_length, NULL, NULL,
+                             0)) {
+    return -1;
+  }
+
+  // path.Append(name) cannot exceed MAX_PATH.
+  int whole_path_limit =
+      std::max(0, MAX_PATH - static_cast<int>(path.value().size()) - 1);
+  return std::min(whole_path_limit, static_cast<int>(max_length));
+}
+
 }  // namespace file_util