Use GUID to generate unique temp file names and retire GetTempFileName

base/files/file_util_win.cc

Index: base/files/file_util_win.cc
diff --git a/base/files/file_util_win.cc b/base/files/file_util_win.cc
index 65dc5ce1e2fe7495624cc6d8c16b954395eb11ac..0e7b748aa61c731cabde41cf26247bfdc4fe91b8 100644
--- a/base/files/file_util_win.cc
+++ b/base/files/file_util_win.cc
@@ -40,6 +40,31 @@ namespace {
 const DWORD kFileShareAll =
     FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE;
 
+// An array consists of digits and alphabet. It is used to generate random
+// prefix of a temp file name which is passed to GetTempFileName Windows API.
+constexpr base::FilePath::CharType kAlphaNumberCharSet[] =

[grt (UTC plus 2), 2017/04/04 12:00:43]

nit: move these constants into the function as static constexpr values.

[chengx, 2017/04/05 05:39:51]

This constant has been removed in the new patch set.

+    FILE_PATH_LITERAL("0123456789abcdefghijklmnopqrstuvwxyz");
+
+// The length of the temp file name prefix, which is used by GetTempFileName
+// Windows API.
+// GetTempFileName uses up to the first three characters of the input prefix
+// string as the prefix of the file name. Therefore, this constant is set to 3.
+// https://msdn.microsoft.com/en-us/library/windows/desktop/aa364991(v=vs.85).aspx
+constexpr int kPrefixLength = 3;
+
+// Get a random prefix with length kPrefixLength of the temp file name.
+// The characters are obtained from kAlphaNumberCharSet.
+FilePath::StringType GetRandomPrefix() {
+  FilePath::StringType temp_file_name_prefix(kPrefixLength, 0);
+
+  for (size_t i = 0; i < kPrefixLength; i++) {

[grt (UTC plus 2), 2017/04/04 12:00:43]

nit: prefer pre-increment; see style guide.

[chengx, 2017/04/05 05:39:51]

This for-loop has been removed in the new patch set.

+    temp_file_name_prefix[i] = kAlphaNumberCharSet[base::RandGenerator(
+        arraysize(kAlphaNumberCharSet) - 1)];
+  }
+
+  return temp_file_name_prefix;
+}
+
 // Deletes all files and directories in a path.
 // Returns false on the first failure it encounters.
 bool DeleteFileRecursive(const FilePath& path,
@@ -342,7 +367,10 @@ bool CreateTemporaryFileInDir(const FilePath& dir, FilePath* temp_file) {
 
   wchar_t temp_name[MAX_PATH + 1];
 
-  if (!GetTempFileName(dir.value().c_str(), L"", 0, temp_name)) {
+  // Supplying a random prefix to GetTempFileName can significantly boost the
+  // chance of successfully creating a new unique name with one shot.
+  if (!GetTempFileName(dir.value().c_str(), GetRandomPrefix().c_str(), 0,
+                       temp_name)) {
     DPLOG(WARNING) << "Failed to get temporary file name in "
                    << UTF16ToUTF8(dir.value());
     return false;