diff --git a/.github/workflows/linux_llvm_cov.yml b/.github/workflows/linux_llvm_cov.yml
index 43fac1e..bd08480 100644
--- a/.github/workflows/linux_llvm_cov.yml
+++ b/.github/workflows/linux_llvm_cov.yml
@@ -34,7 +34,7 @@ jobs:
           cd tests
           ./test_rest_rpc
           llvm-profdata merge -sparse test_rest_rpc-*.profraw -o test_rest_rpc.profdata
-          llvm-cov show ./test_rest_rpc -instr-profile=test_rest_rpc.profdata -format=html -output-dir=../.coverage_llvm_cov -ignore-filename-regex="examples|thirdparty|tests" -show-instantiations=false
+          llvm-cov show ./test_rest_rpc -instr-profile=test_rest_rpc.profdata -format=html -output-dir=../.coverage_llvm_cov -ignore-filename-regex="string_view.hpp|nonstd_any.hpp|examples|thirdparty|tests" -show-instantiations=false
           echo "Done!"
 
       - name: Upload Coverage Results
@@ -49,7 +49,7 @@ jobs:
           echo "Code Coverage Report" > tmp.log
           echo "for detail, [goto summary](https://github.com/${{ github.repository_owner }}/${{ github.event.repository.name }}/actions/runs/${{github.run_id}}) download Artifacts `llvm-cov`" >> tmp.log
           echo "\`\`\`" >> tmp.log
-          llvm-cov report ./test_rest_rpc -instr-profile=test_rest_rpc.profdata -ignore-filename-regex="examples|thirdparty|tests" -show-region-summary=false >> tmp.log
+          llvm-cov report ./test_rest_rpc -instr-profile=test_rest_rpc.profdata -ignore-filename-regex="string_view.hpp|nonstd_any.hpp|examples|thirdparty|tests" -show-region-summary=false >> tmp.log
           echo "\`\`\`" >> tmp.log
 
       - name: Create Comment
diff --git a/include/rest_rpc/rpc_server.h b/include/rest_rpc/rpc_server.h
index 11fcfa0..ee60da9 100644
--- a/include/rest_rpc/rpc_server.h
+++ b/include/rest_rpc/rpc_server.h
@@ -63,6 +63,11 @@ public:
     router_.register_handler<is_pub>(name, f, self);
   }
 
+  void
+  set_error_callback(std::function<void(asio::error_code, string_view)> f) {
+    err_cb_ = std::move(f);
+  }
+
   void set_conn_timeout_callback(std::function<void(int64_t)> callback) {
     conn_timeout_callback_ = std::move(callback);
   }
@@ -169,7 +174,11 @@ private:
       }
     }
   }
-
+  void error_callback(const asio::error_code &ec, string_view msg) {
+    if (err_cb_) {
+      err_cb_(ec, msg);
+    }
+  }
   template <typename T>
   void publish(std::string key, std::string token, T data) {
     {
@@ -182,13 +191,19 @@ private:
         get_shared_data<T>(std::move(data));
     std::unique_lock<std::mutex> lock(sub_mtx_);
     auto range = sub_map_.equal_range(key + token);
-    for (auto it = range.first; it != range.second; ++it) {
-      auto conn = it->second.lock();
-      if (conn == nullptr || conn->has_closed()) {
-        continue;
-      }
+    if (range.first != range.second) {
+      for (auto it = range.first; it != range.second; ++it) {
+        auto conn = it->second.lock();
+        if (conn == nullptr || conn->has_closed()) {
+          continue;
+        }
 
-      conn->publish(key + token, *shared_data);
+        conn->publish(key + token, *shared_data);
+      }
+    } else {
+      error_callback(
+          asio::error::make_error_code(asio::error::invalid_argument),
+          "The subscriber of the key: " + key + " does not exist.");
     }
   }
 
@@ -255,6 +270,7 @@ private:
 
   asio::signal_set signals_;
 
+  std::function<void(asio::error_code, string_view)> err_cb_;
   std::function<void(int64_t)> conn_timeout_callback_;
   std::function<void(std::shared_ptr<connection>, std::string)>
       on_net_err_callback_ = nullptr;
diff --git a/tests/test_rest_rpc.cpp b/tests/test_rest_rpc.cpp
index f3048a5..91cf95e 100644
--- a/tests/test_rest_rpc.cpp
+++ b/tests/test_rest_rpc.cpp
@@ -13,6 +13,7 @@ struct dummy {
 };
 
 std::string echo(rpc_conn conn, const std::string &src) { return src; }
+std::string echo_empty(rpc_conn conn, const std::string &src) { return ""; }
 
 struct person {
   int id;
@@ -37,10 +38,35 @@ void hello(rpc_conn conn, const std::string &str) {
   std::cout << "hello " << str << std::endl;
 }
 
+// if you want to response later, you can use async model, you can control when
+// to response
+void delay_echo(rpc_conn conn, const std::string &src) {
+  auto sp = conn.lock();
+  sp->set_delay(true);
+  auto req_id = sp->request_id(); // note: you need keep the request id at that
+  // time, and pass it into the async thread
+  std::thread thd([conn, req_id, src] {
+    std::this_thread::sleep_for(std::chrono::seconds(1));
+    auto conn_sp = conn.lock();
+    if (conn_sp) {
+      conn_sp->pack_and_response(req_id, std::move(src));
+    }
+  });
+  thd.detach();
+}
+
+struct empty_obj {
+  MSGPACK_DEFINE()
+};
+
+empty_obj get_empty_obj(rpc_conn conn) { return {}; }
+
 TEST_CASE("test_client_reconnect") {
   rpc_client client;
   client.enable_auto_reconnect(); // automatic reconnect
   client.enable_auto_heartbeat(); // automatic heartbeat
+  client.set_connect_timeout(1000);
+  client.set_reconnect_count(10);
   client.set_error_callback([](asio::error_code ec) {
     std::cout << "line: " << __LINE__ << ", msg: " << ec.message() << std::endl;
   });
@@ -141,6 +167,28 @@ TEST_CASE("test_client_sync_call_return_void") {
   client.call<>("echo");
 }
 
+TEST_CASE("test_client_async_call_empty_obj") {
+  rpc_server server(9000, std::thread::hardware_concurrency());
+  server.register_handler("get_empty_obj", get_empty_obj);
+  server.async_run();
+  std::this_thread::sleep_for(std::chrono::milliseconds(200));
+
+  rpc_client client("127.0.0.1", 9000);
+  bool r = client.connect();
+  CHECK(r);
+
+  client.set_error_callback(
+      [](asio::error_code ec) { std::cout << ec.message() << std::endl; });
+
+  auto f = client.async_call<FUTURE>("get_empty_obj");
+  if (f.wait_for(std::chrono::milliseconds(50)) ==
+      std::future_status::timeout) {
+    std::cout << "timeout" << std::endl;
+  } else {
+    auto p = f.get().as<empty_obj>();
+  }
+}
+
 TEST_CASE("test_client_async_call") {
   rpc_server server(9000, std::thread::hardware_concurrency());
   server.register_handler("get_person", get_person);
@@ -180,6 +228,7 @@ TEST_CASE("test_client_async_call_not_connect") {
 TEST_CASE("test_client_async_call_with_timeout") {
   rpc_server server(9000, std::thread::hardware_concurrency());
   server.register_handler("echo", echo);
+  server.register_handler("get_person", get_person);
   server.async_run();
   std::this_thread::sleep_for(std::chrono::milliseconds(200));
 
@@ -191,15 +240,41 @@ TEST_CASE("test_client_async_call_with_timeout") {
   client.async_call<0>(
       "echo",
       [](const asio::error_code &ec, string_view data) {
-        std::cout << "error code " << ec << ", err msg: " << data << '\n';
+        if (ec)
+          std::cout << "error code: " << ec << ", err msg: " << data << '\n';
       },
       test);
   client.async_call<>(
       "echo",
-      [](const asio::error_code &ec, string_view data) {
-        std::cout << "error code " << ec << ", err msg: " << data << '\n';
+      [&client](const asio::error_code &ec, string_view data) {
+        std::cout << "req id : " << client.reqest_id() << '\n';
+        if (ec)
+          std::cout << "error code: " << ec << ", err msg: " << data << '\n';
       },
       test);
+  client.async_call<>(
+      "get_person",
+      [&client](const asio::error_code &ec, string_view data) {
+        if (ec) {
+          std::cout << "error code: " << ec << ", err msg: " << data << '\n';
+          return;
+        }
+        auto p = as<person>(data);
+        CHECK_EQ(p.id, 1);
+        CHECK_EQ(p.age, 20);
+        CHECK_EQ(p.name, "tom");
+      },
+      test);
+  auto f = client.async_call<FUTURE>("get_person");
+  if (f.wait_for(std::chrono::milliseconds(500)) ==
+      std::future_status::timeout) {
+    std::cout << "timeout" << std::endl;
+  } else {
+    auto p = f.get().as<person>();
+    CHECK_EQ(p.id, 1);
+    CHECK_EQ(p.age, 20);
+    CHECK_EQ(p.name, "tom");
+  }
 }
 
 TEST_CASE("test_client_subscribe") {
@@ -232,6 +307,45 @@ TEST_CASE("test_client_subscribe") {
   thd.join();
 }
 
+TEST_CASE("test_client_subscribe_not_exist_key") {
+  rpc_server server(9000, std::thread::hardware_concurrency());
+  server.register_handler("publish",
+                          [&server](rpc_conn conn, std::string key,
+                                    std::string token, std::string val) {
+                            server.publish(std::move(key), std::move(val));
+                          });
+  bool stop = false;
+  server.set_error_callback([&stop](asio::error_code ec, string_view msg) {
+    std::cout << "line: " << __LINE__ << ", msg: " << ec.message() << " -- "
+              << msg << std::endl;
+    CHECK_EQ(ec, asio::error::invalid_argument);
+    stop = true;
+  });
+  server.set_conn_timeout_callback([](int64_t conn_id) {
+    std::cout << "connect id : " << conn_id << " timeout \n";
+  });
+  std::thread thd([&server, &stop] {
+    while (!stop) {
+      server.publish("key", "hello subscriber");
+      std::this_thread::sleep_for(std::chrono::milliseconds(500));
+    }
+  });
+  server.async_run();
+  std::this_thread::sleep_for(std::chrono::milliseconds(200));
+  rpc_client client;
+  bool r = client.connect("127.0.0.1", 9000);
+  CHECK(r);
+  client.set_error_callback([&stop](asio::error_code ec) {
+    std::cout << "line: " << __LINE__ << ", msg: " << ec.value() << " -- "
+              << ec.message() << std::endl;
+  });
+  client.subscribe("key1", [&stop](string_view data) {
+    CHECK(data != "hello subscriber");
+    stop = true;
+  });
+  thd.join();
+}
+
 TEST_CASE("test_server_publish_encode_msg") {
   rpc_server server(9000, std::thread::hardware_concurrency());
   server.register_handler("publish",
@@ -294,6 +408,40 @@ TEST_CASE("test_client_subscribe_by_token") {
   thd.join();
 }
 
+TEST_CASE("test_client_publish_and_subscribe_by_token") {
+  rpc_server server(9000, std::thread::hardware_concurrency());
+  server.register_handler("publish_by_token", [&server](rpc_conn conn,
+                                                        std::string key,
+                                                        std::string token,
+                                                        std::string val) {
+    server.publish_by_token(std::move(key), std::move(token), std::move(val));
+  });
+  bool stop = false;
+  std::thread thd([&server, &stop] {
+    while (!stop) {
+      auto list = server.get_token_list();
+      for (auto &token : list) {
+        server.publish_by_token("key", token, "hello token subscriber");
+      }
+      std::this_thread::sleep_for(std::chrono::milliseconds(50));
+    }
+  });
+  server.async_run();
+  std::this_thread::sleep_for(std::chrono::milliseconds(200));
+  std::string client_token =
+      "048a796c8a3c6a6b7bd1223bf2c8cee05232e927b521984ba417cb2fca6df9d1";
+  rpc_client client;
+  bool r = client.connect("127.0.0.1", 9000);
+  CHECK(r);
+  client.publish_by_token("key", client_token, "hello token subscriber");
+  client.subscribe("key", client_token, [&stop](string_view data) {
+    std::cout << data << "\n";
+    CHECK_EQ(data, "hello token subscriber");
+    stop = true;
+  });
+  thd.join();
+}
+
 TEST_CASE("test_server_callback") {
   rpc_server server(9000, std::thread::hardware_concurrency());
   dummy d;
@@ -325,4 +473,16 @@ TEST_CASE("test_server_user_data") {
   bool r = client.connect();
   CHECK(r);
   client.call<>("server_user_data");
+}
+TEST_CASE("test_server_delay_response") {
+  rpc_server server(9000, std::thread::hardware_concurrency());
+  server.register_handler("delay_echo", delay_echo);
+  server.async_run();
+  std::this_thread::sleep_for(std::chrono::milliseconds(200));
+
+  rpc_client client("127.0.0.1", 9000);
+  bool r = client.connect();
+  CHECK(r);
+  auto result = client.call<std::string>("delay_echo", "test_delay_echo");
+  CHECK_EQ(result, "test_delay_echo");
 }
\ No newline at end of file