Android handler: Fix name collision.

shell/android/android_handler.cc

 // 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 "shell/android/android_handler.h"
 
+#include <fcntl.h>
+
 #include "base/android/jni_android.h"
 #include "base/android/jni_string.h"
 #include "base/files/file_path.h"
 #include "base/logging.h"
 #include "base/message_loop/message_loop.h"
+#include "base/rand_util.h"
 #include "base/run_loop.h"
 #include "base/scoped_native_library.h"
+#include "base/strings/string_number_conversions.h"
 #include "base/trace_event/trace_event.h"
 #include "jni/AndroidHandler_jni.h"
 #include "mojo/common/data_pipe_utils.h"
 #include "mojo/public/c/system/main.h"
 #include "mojo/public/cpp/application/application_impl.h"
 #include "shell/android/run_android_application_function.h"
 #include "shell/native_application_support.h"
 
 using base::android::AttachCurrentThread;
 using base::android::ScopedJavaLocalRef;
@@ skipping 123 matching lines @@
           *extracted_dir = base::FilePath(
               std::string(reinterpret_cast<char*>(&extracted_path.front()),
                           extracted_path.size()));
           *cache_dir = base::FilePath(std::string(
               reinterpret_cast<char*>(&cache_path.front()), cache_path.size()));
         }
         callback.Run();
       });
 }
 
+jstring CreateTemporaryFile(JNIEnv* env,
+                            jclass jcaller,
+                            jstring j_directory,
+                            jstring j_basename,
+                            jstring j_extension) {
+  std::string basename(ConvertJavaStringToUTF8(env, j_basename));
+  std::string extension(ConvertJavaStringToUTF8(env, j_extension));
+  base::FilePath directory(ConvertJavaStringToUTF8(env, j_directory));
+
+  for (;;) {
+    std::string random = base::RandBytesAsString(16);
+    std::string filename =
+        basename + base::HexEncode(random.data(), random.size()) + extension;
+    base::FilePath temporary_file = directory.Append(filename);
+    int fd = open(temporary_file.value().c_str(), O_CREAT | O_EXCL, 0600);

[blundell, 2015/05/13 09:16:43]

Are you doing this construction in C++ rather than Java so that you can do this
atomic check that the file doesn't already exist?

[qsr, 2015/05/13 09:32:05]

Nope, I do this in C++ because:
1) I now do not trust the random generator
2) There is no easy way to convert bytes to hexadecimal values

+    if (fd != -1) {
+      close(fd);
+      return ConvertUTF8ToJavaString(env, temporary_file.value()).Release();
+    }
+  }
+}
+
 bool RegisterAndroidHandlerJni(JNIEnv* env) {
   return RegisterNativesImpl(env);
 }
 
 }  // namespace shell