Add GenerateAppId, to generate a random 64-bit app ID encoded in base64.

PiperOrigin-RevId: 248593579

Author: jonsimantov

app/instance_id/instance_id_desktop_impl.cc

@@ -18,8 +18,10 @@
 
 #include "app/instance_id/iid_data_generated.h"
 #include "app/src/app_identifier.h"
+#include "app/src/base64.h"
 #include "app/src/cleanup_notifier.h"
 #include "app/src/time.h"
+#include "app/src/uuid.h"
 #include "flatbuffers/flexbuffers.h"
 
 namespace firebase {
@@ -190,9 +192,9 @@ bool InstanceIdDesktopImpl::SaveToStorage() {
 
   std::vector<flatbuffers::Offset<Token>> token_offsets;
   for (auto it = tokens_.begin(); it != tokens_.end(); ++it) {
-    token_offsets.push_back(CreateTokenDirect(
-        builder, it->first.c_str() /* scope */,
-        it->second.c_str() /* token */));
+    token_offsets.push_back(CreateTokenDirect(builder,
+                                              it->first.c_str() /* scope */,
+                                              it->second.c_str() /* token */));
   }
   auto iid_data_table = CreateInstanceIdDesktopDataDirect(
       builder, instance_id_.c_str(), checkin_data_.device_id.c_str(),
@@ -301,6 +303,11 @@ bool InstanceIdDesktopImpl::InitialOrRefreshCheckin() {
     LoadFromStorage();
   }
 
+  // If we don't have an instance_id_ yet, generate one now.
+  if (instance_id_.empty()) {
+    instance_id_ = GenerateAppId();
+  }
+
   // If we've already checked in.
   if (checkin_data_.last_checkin_time_ms > 0) {
     FIREBASE_ASSERT(!checkin_data_.device_id.empty() &&
@@ -433,6 +440,29 @@ bool InstanceIdDesktopImpl::InitialOrRefreshCheckin() {
   return true;
 }
 
+std::string InstanceIdDesktopImpl::GenerateAppId() {
+  firebase::internal::Uuid uuid;
+  uuid.Generate();
+  // Collapse into 8 bytes, forcing the top 4 bits to be 0x70.
+  uint8_t buffer[8];
+  buffer[0] = ((uuid.data[0] ^ uuid.data[8]) & 0x0f) | 0x70;
+  buffer[1] = uuid.data[1] ^ uuid.data[9];
+  buffer[2] = uuid.data[2] ^ uuid.data[10];
+  buffer[3] = uuid.data[3] ^ uuid.data[11];
+  buffer[4] = uuid.data[4] ^ uuid.data[12];
+  buffer[5] = uuid.data[5] ^ uuid.data[13];
+  buffer[6] = uuid.data[6] ^ uuid.data[14];
+  buffer[7] = uuid.data[7] ^ uuid.data[15];
+
+  std::string input(reinterpret_cast<char*>(buffer), sizeof(buffer));
+  std::string output;
+
+  if (firebase::internal::Base64Encode(input, &output)) {
+    return output;
+  }
+  return "";  // Error encoding.
+}
+
 }  // namespace internal
 }  // namespace instance_id
 }  // namespace firebase

app/instance_id/instance_id_desktop_impl.h

@@ -199,13 +199,17 @@ class InstanceIdDesktopImpl {
   // Delete the instance ID from local secure storage. Blocking.
   bool DeleteFromStorage();
 
-  // Used to wait for async storage functions to finish.
-  Semaphore storage_semaphore_;
-
   // Fetch the current device ID and security token or check-in to retrieve
   // a new device ID and security token.
   bool InitialOrRefreshCheckin();
 
+  // Generate a new appid. This is 4 bits of 0x7 followed by 60 bits of
+  // randomness, then base64-encoded until golden brown.
+  std::string GenerateAppId();
+
+  // Used to wait for async storage functions to finish.
+  Semaphore storage_semaphore_;
+
   // Future manager of this object
   FutureManager future_manager_;