Add more Rand helper methods

PiperOrigin-RevId: 491409479

internal/crypto/random.cc

@@ -16,6 +16,8 @@
 
 #include <stddef.h>
 
+#include <string>
+
 #include <openssl/rand.h>
 
 namespace crypto {
@@ -28,4 +30,11 @@ void RandBytes(absl::Span<uint8_t> bytes) {
   RandBytes(bytes.data(), bytes.size());
 }
 
+std::string RandBytes(size_t length) {
+  std::string result(length, 0);
+  RandBytes(const_cast<std::string::value_type *>(result.data()),
+            result.size());
+  return result;
+}
+
 }  // namespace crypto

internal/crypto/random.h

@@ -17,6 +17,8 @@
 
 #include <stddef.h>
 
+#include <string>
+
 #include "absl/types/span.h"
 #include "internal/crypto/crypto_export.h"
 
@@ -29,6 +31,19 @@ CRYPTO_EXPORT void RandBytes(void *bytes, size_t length);
 
 // Fills |bytes| with cryptographically-secure random bits.
 CRYPTO_EXPORT void RandBytes(absl::Span<uint8_t> bytes);
+
+// Returns |length| random bytes.
+CRYPTO_EXPORT std::string RandBytes(size_t length);
+
+// Creates an object of type T initialized with random data.
+// This template should be used for simple data types: int, char, etc.
+template <typename T>
+T RandData() {
+  T data;
+  RandBytes(&data, sizeof(data));
+  return data;
+}
+
 }  // namespace crypto
 
 #endif  // THIRD_PARTY_NEARBY_INTERNAL_CRYPTO_RANDOM_H_

internal/crypto/random_unittest.cc

@@ -23,6 +23,9 @@
 
 // Basic functionality tests. Does NOT test the security of the random data.
 
+namespace crypto {
+namespace {
+
 // Ensures we don't have all trivial data, i.e. that the data is indeed random.
 // Currently, that means the bytes cannot be all the same (e.g. all zeros).
 bool IsTrivial(const std::string& bytes) {
@@ -36,6 +39,28 @@ bool IsTrivial(const std::string& bytes) {
 
 TEST(RandBytes, RandBytes) {
   std::string bytes(16, '\0');
-  crypto::RandBytes(nearbybase::WriteInto(&bytes, bytes.size()), bytes.size());
+  RandBytes(nearbybase::WriteInto(&bytes, bytes.size()), bytes.size());
   EXPECT_TRUE(!IsTrivial(bytes));
 }
+
+TEST(RandBytes, RandomString) {
+  constexpr size_t kSize = 30;
+
+  std::string bytes = RandBytes(kSize);
+
+  EXPECT_EQ(bytes.size(), kSize);
+  EXPECT_TRUE(!IsTrivial(bytes));
+}
+
+TEST(RandBytes, RandData) {
+  uint64_t x = RandData<uint64_t>();
+  uint64_t y = RandData<uint64_t>();
+
+  // Once in a billion years, consecutively generated random numbers will be
+  // the same and the test will fail.
+  EXPECT_NE(x, y);
+  EXPECT_NE(x >> 32, x & 0xFFFFFFFF);
+}
+
+}  // namespace
+}  // namespace crypto