Use alphanumeric characters for PresenceDevice endpoint id generation

PiperOrigin-RevId: 540321021

presence/BUILD

@@ -86,11 +86,10 @@ cc_library(
         "scan_request_builder.h",
     ],
     deps = [
-        "//internal/crypto",
         "//internal/interop:device",
+        "//internal/platform:base",
         "//internal/platform:connection_info",
         "//internal/platform:logging",
-        "//internal/platform:types",
         "//internal/platform/implementation:types",
         "//internal/proto:credential_cc_proto",
         "//internal/proto:metadata_cc_proto",

presence/presence_device.cc

@@ -17,20 +17,27 @@
 #include <string>
 #include <vector>
 
-#include "internal/platform/implementation/crypto.h"
 #include "internal/interop/device.h"
 #include "internal/platform/ble_connection_info.h"
 #include "internal/platform/implementation/system_clock.h"
+#include "internal/platform/prng.h"
 #include "presence/device_motion.h"
 
 namespace nearby {
 namespace presence {
 
 namespace {
+constexpr char kEndpointIdChars[] = {
+    'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L',
+    'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
+    'Y', 'Z', '1', '2', '3', '4', '5', '6', '7', '8', '9', '0'};
+
 std::string GenerateRandomEndpointId() {
   std::string result(kEndpointIdLength, 0);
-  crypto::RandBytes(const_cast<std::string::value_type*>(result.data()),
-                    result.size());
+  nearby::Prng prng;
+  for (int i = 0; i < kEndpointIdLength; i++) {
+    result[i] = kEndpointIdChars[prng.NextUint32() % sizeof(kEndpointIdChars)];
+  }
   return result;
 }
 }  // namespace

presence/presence_device_test.cc

@@ -117,6 +117,13 @@ TEST(PresenceDeviceTest, TestEndpointIdIsCorrectLength) {
   EXPECT_EQ(device.GetEndpointId().length(), kEndpointIdLength);
 }
 
+TEST(PresenceDeviceTest, TestEndpointIdIsRandom) {
+  Metadata metadata = CreateTestMetadata();
+  PresenceDevice device = PresenceDevice({kDefaultMotionType}, metadata);
+  EXPECT_EQ(device.GetEndpointId().length(), kEndpointIdLength);
+  EXPECT_NE(device.GetEndpointId(), std::string(kEndpointIdLength, 0));
+}
+
 }  // namespace
 }  // namespace presence
 }  // namespace nearby