Allow passing serialized FuzzTest configuration in env.

When the env field is set, Centipede will not query the configuration using the runner callback.

Eventually, we will merge the Configuration fields used in Centipede as proper env fields, and eliminate the configuration callback.

PiperOrigin-RevId: 722681102

centipede/centipede_interface.cc

@@ -729,7 +729,10 @@ int CentipedeMain(const Environment &env,
   // We don't update the corpus database for standalone binaries (i.e., when
   // `env.has_input_wildcards` is true).
   if (!env.binary.empty() && !env.has_input_wildcards) {
-    const absl::StatusOr<std::string> serialized_target_config = [&] {
+    const auto serialized_target_config = [&]() -> absl::StatusOr<std::string> {
+      if (!env.fuzztest_configuration.empty()) {
+        return env.fuzztest_configuration;
+      }
       ScopedCentipedeCallbacks scoped_callbacks(callbacks_factory, env);
       return scoped_callbacks.callbacks()->GetSerializedTargetConfig();
     }();

centipede/environment.h

@@ -130,6 +130,9 @@ struct Environment {
   // If set, operate on the corpus database for a single test specified by
   // FuzzTest instead of all the tests.
   bool fuzztest_single_test_mode = false;
+  // If set, deserializes the configuration from the value instead of querying
+  // the configuration via runner callbacks.
+  std::string fuzztest_configuration;
 
   // Command line-related fields -----------------------------------------------
 

fuzztest/internal/centipede_adaptor.cc

@@ -209,6 +209,15 @@ centipede::Environment CreateCentipedeEnvironmentFromConfiguration(
       run_mode == RunMode::kUnitTest) {
     total_time_limit = kUnitTestDefaultDuration;
   }
+  {
+    Configuration single_test_configuration = configuration;
+    single_test_configuration.fuzz_tests_in_current_shard = {
+        std::string{test_name}};
+    single_test_configuration.time_limit = total_time_limit;
+    single_test_configuration.time_budget_type = TimeBudgetType::kTotal;
+    env.fuzztest_configuration = single_test_configuration.Serialize();
+  }
+
   absl::StrAppend(&env.binary,
                   " --" FUZZTEST_FLAG_PREFIX
                   "internal_override_total_time_limit=",