[fuzzing] Allow server fuzzer to take multiple connection requests at the same time (#35645)

Closes #35645

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/35645 from ctiller:shush-multipass e63e1e5ddb
PiperOrigin-RevId: 600998039

test/core/end2end/fuzzers/client_fuzzer.cc

@@ -58,7 +58,7 @@ class ClientFuzzer final : public BasicFuzzer {
       : BasicFuzzer(msg.event_engine_actions()) {
     ExecCtx exec_ctx;
     UpdateMinimumRunTime(
-        ScheduleReads(msg.network_input(), mock_endpoint_, engine()));
+        ScheduleReads(msg.network_input()[0], mock_endpoint_, engine()));
     ChannelArgs args =
         CoreConfiguration::Get()
             .channel_args_preconditioning()
@@ -101,6 +101,7 @@ DEFINE_PROTO_FUZZER(const fuzzer_input::Msg& msg) {
   if (squelch && !grpc_core::GetEnv("GRPC_TRACE_FUZZER").has_value()) {
     gpr_set_log_function(dont_log);
   }
+  if (msg.network_input().size() != 1) return;
   grpc_core::ApplyFuzzConfigVars(msg.config_vars());
   grpc_core::TestOnlyReloadExperimentsFromConfigVariables();
   grpc_core::testing::ClientFuzzer(msg).Run(msg.api_actions());

test/core/end2end/fuzzers/fuzzer_input.proto

@@ -205,7 +205,7 @@ message NetworkInput {
 }
 
 message Msg {
-    NetworkInput network_input = 1;
+    repeated NetworkInput network_input = 1;
     repeated api_fuzzer.Action api_actions = 2;
     fuzzing_event_engine.Actions event_engine_actions = 3;
     grpc.testing.FuzzConfigVars config_vars = 4;

test/core/end2end/fuzzers/server_fuzzer.cc

@@ -51,9 +51,10 @@ class ServerFuzzer final : public BasicFuzzer {
     grpc_server_add_http2_port(server_, "0.0.0.0:1234", creds);
     grpc_server_credentials_release(creds);
     grpc_server_start(server_);
-    UpdateMinimumRunTime(
-        ScheduleConnection(msg.network_input(), engine(),
-                           FuzzingEnvironment{resource_quota()}, 1234));
+    for (const auto& input : msg.network_input()) {
+      UpdateMinimumRunTime(ScheduleConnection(
+          input, engine(), FuzzingEnvironment{resource_quota()}, 1234));
+    }
   }
 
   ~ServerFuzzer() { GPR_ASSERT(server_ == nullptr); }