4 files changed, 139 insertions, 0 deletions
diff --git a/Firestore/src/support/CMakeLists.txt b/Firestore/src/support/CMakeLists.txt
new file mode 100644
index 0000000..8110c6f
--- /dev/null
+++ b/Firestore/src/support/CMakeLists.txt
@@ -0,0 +1,18 @@
+# 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.
+
+add_library(
+  firestore_support
+  secure_random_arc4random.cc
+)
diff --git a/Firestore/src/support/port.h b/Firestore/src/support/port.h
new file mode 100644
index 0000000..6af898a
--- /dev/null
+++ b/Firestore/src/support/port.h
@@ -0,0 +1,33 @@
+/*
+ * 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.
+ */
+
+#ifndef FIRESTORE_SRC_SUPPORT_PORT_H_
+#define FIRESTORE_SRC_SUPPORT_PORT_H_
+
+#if defined(__APPLE__)
+// On Apple platforms we support building via Cocoapods without CMake. When
+// building this way we can't test the presence of features so predefine all
+// the platform-support feature macros to their expected values.
+
+// All supported Apple platforms have arc4random(3).
+#define HAVE_ARC4RANDOM 1
+
+#else
+
+#error "Unknown platform."
+#endif  // defined(__APPLE__)
+
+#endif  // FIRESTORE_SRC_SUPPORT_PORT_H_
diff --git a/Firestore/src/support/secure_random.h b/Firestore/src/support/secure_random.h
new file mode 100644
index 0000000..92a3eaf
--- /dev/null
+++ b/Firestore/src/support/secure_random.h
@@ -0,0 +1,55 @@
+/*
+ * 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.
+ */
+
+#ifndef FIRESTORE_SRC_SUPPORT_SECURE_RANDOM_H_
+#define FIRESTORE_SRC_SUPPORT_SECURE_RANDOM_H_
+
+#include <stdint.h>
+
+#include <limits>
+
+namespace firestore {
+
+// A "secure" pseudorandom number generator, suitable for generating
+// unguessable identifiers. This exists because
+//
+//   * std::mt19937 is blazing fast but its outputs can be guessed once enough
+//     previous outputs have been observed.
+//   * std::random_device isn't guaranteed to come from a secure PRNG or be
+//     fast.
+//
+// The implementation satisfies the C++11 UniformRandomBitGenerator concept and
+// delegates to an implementation that generates high quality random values
+// quickly with periodic reseeding.
+class SecureRandom {
+ public:
+  // C++11 UniformRandomBitGenerator interface
+  using result_type = uint32_t;
+
+  static constexpr result_type min() {
+    return std::numeric_limits<result_type>::min();
+  }
+
+  static constexpr result_type max() {
+    return std::numeric_limits<result_type>::max();
+  }
+
+  result_type operator()();
+};
+
+}  // namespace firestore
+
+#endif  // FIRESTORE_SRC_SUPPORT_SECURE_RANDOM_H_
diff --git a/Firestore/src/support/secure_random_arc4random.cc b/Firestore/src/support/secure_random_arc4random.cc
new file mode 100644
index 0000000..4cd7f9d
--- /dev/null
+++ b/Firestore/src/support/secure_random_arc4random.cc
@@ -0,0 +1,33 @@
+/*
+ * 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/src/support/secure_random.h"
+
+#include "Firestore/src/support/port.h"
+
+#if HAVE_ARC4RANDOM
+
+#include <stdlib.h>
+
+namespace firestore {
+
+SecureRandom::result_type SecureRandom::operator()() {
+  return arc4random();
+}
+
+}  // namespace firestore
+
+#endif  // HAVE_ARC4RANDOM