Fix bugs; Add doc comments

src/tcp.cpp

@@ -39,7 +39,6 @@ inline sockaddr_in get_local_address(uint16_t port) {
 }
 
 
-
 } // namespace
 
 
@@ -74,14 +73,14 @@ std::expected<void, int> NonBlockingServer::start_listening(uint16_t port) {
                sizeof(serverAddress)) != 0) {
         spdlog::error("tcp::NonBlockingServer: bind() failed with errno={}",
                       errno);
-        close(m_serverSocket);
+        close_server_socket();
         return std::unexpected{errno};
     };
 
     if (::listen(m_serverSocket, 1) != 0) {
         spdlog::error("tcp::NonBlockingServer: listen() failed with errno={}",
                       errno);
-        close(m_serverSocket);
+        close_server_socket();
         return std::unexpected{errno};
     }
 
@@ -181,6 +180,7 @@ NonBlockingServer::create_server_socket() {
     if (m_serverSocket < 1) {
         spdlog::error("tcp::NonBlockingServer: socket() failed with errno={}",
                       errno);
+        close_server_socket();
         return std::unexpected{errno};
     }
 
@@ -291,6 +291,15 @@ void NonBlockingClient::disconnect() {
     close_socket();
 }
 
+///
+/// @brief Get last known connection status
+/// @return - expected(EINPROGRESS) if connection is still being attempted
+///         - expected(EISCONN) if already connected
+///         - expected(error code) if an error occurred during connection (e.g.,
+///           ECONNREFUSED)
+///         - unexpected(errno) if an error occurred while checking connection
+///           status
+///
 [[nodiscard]] std::expected<int, int>
 NonBlockingClient::get_last_connection_status() {
     if (!m_startedNewConAttempt) return m_lastKnownConStatus;
@@ -369,6 +378,7 @@ NonBlockingClient::recv(std::span<std::byte> buffer) {
     if (m_socket < 1) {
         spdlog::error("tcp::NonBlockingClient: socket() failed with errno={}",
                       errno);
+        close_socket();
         return std::unexpected{errno};
     }
 
@@ -409,6 +419,11 @@ void NonBlockingClient::close_socket() {
     m_pfdIn.fd  = -1;
 }
 
+
+///
+/// @return true if there is new output event, i.e., the connect() operation has
+/// completed (successfully or not)
+///
 [[nodiscard]] std::expected<bool, int>
 NonBlockingClient::socket_has_new_output_event() {
     int ret = poll(&m_pfdOut, 1, 0);