[fuzzing] Add ability to listen to ports to api-fuzzer (#35273)

Unsure when this got dropped!

Closes #35273

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/35273 from ctiller:server-port be94e30a06
PiperOrigin-RevId: 589919718

test/core/end2end/fuzzers/api_fuzzer.cc

@@ -369,6 +369,18 @@ static grpc_channel_credentials* ReadChannelCreds(
   }
 }
 
+static grpc_server_credentials* ReadServerCreds(
+    const api_fuzzer::ServerCreds& creds) {
+  switch (creds.type_case()) {
+    case api_fuzzer::ServerCreds::TYPE_NOT_SET:
+      return nullptr;
+    case api_fuzzer::ServerCreds::kInsecureCreds:
+      return grpc_insecure_server_credentials_create();
+    case api_fuzzer::ServerCreds::kNull:
+      return nullptr;
+  }
+}
+
 namespace grpc_core {
 namespace testing {
 
@@ -428,6 +440,12 @@ ApiFuzzer::Result ApiFuzzer::CreateServer(
     server_ = grpc_server_create(args.ToC().get(), nullptr);
     GPR_ASSERT(server_ != nullptr);
     grpc_server_register_completion_queue(server_, cq(), nullptr);
+    for (const auto& http2_port : create_server.http2_ports()) {
+      auto* creds = ReadServerCreds(http2_port.server_creds());
+      auto addr = absl::StrCat("localhost:", http2_port.port());
+      grpc_server_add_http2_port(server_, addr.c_str(), creds);
+      grpc_server_credentials_release(creds);
+    }
     grpc_server_start(server_);
     ResetServerState();
   } else {

test/core/end2end/fuzzers/api_fuzzer.proto

@@ -78,6 +78,13 @@ message ChannelCreds {
     }
 }
 
+message ServerCreds {
+    oneof type {
+        Empty insecure_creds = 1;
+        Empty null = 2;
+    }    
+}
+
 message Metadatum {
     StringSlice key = 1;
     ByteSlice value = 2;
@@ -89,8 +96,14 @@ message CreateChannel {
     ChannelCreds channel_creds = 3;
 }
 
+message Http2ServerPort {
+    int32 port = 1;
+    ServerCreds server_creds = 2;
+}
+
 message CreateServer {
     grpc.testing.FuzzingChannelArgs channel_args = 1;
+    repeated Http2ServerPort http2_ports = 2;
 }
 
 message CreateCall {