1 files changed, 56 insertions, 0 deletions
diff --git a/Firestore/core/src/firebase/firestore/util/autoid.cc b/Firestore/core/src/firebase/firestore/util/autoid.cc
new file mode 100644
index 0000000..10a2cde
--- /dev/null
+++ b/Firestore/core/src/firebase/firestore/util/autoid.cc
@@ -0,0 +1,56 @@
+/*
+ * Copyright 2017 Google
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "Firestore/core/src/firebase/firestore/util/autoid.h"
+
+#include <random>
+#include <string>
+
+#include "Firestore/core/src/firebase/firestore/util/secure_random.h"
+
+namespace firebase {
+namespace firestore {
+namespace util {
+
+namespace {
+
+const int kAutoIdLength = 20;
+const char kAutoIdAlphabet[] =
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
+
+SecureRandom shared_random;
+
+}  // namespace
+
+std::string CreateAutoId() {
+  std::string auto_id;
+  auto_id.reserve(kAutoIdLength);
+
+  // -2 here because:
+  //   * sizeof(kAutoIdAlphabet) includes the trailing null terminator
+  //   * uniform_int_distribution is inclusive on both sizes
+  std::uniform_int_distribution<int> letters(0, sizeof(kAutoIdAlphabet) - 2);
+
+  for (int i = 0; i < kAutoIdLength; i++) {
+    int rand_index = letters(shared_random);
+    auto_id.append(1, kAutoIdAlphabet[rand_index]);
+  }
+  return auto_id;
+}
+
+}  // namespace util
+}  // namespace firestore
+}  // namespace firebase