Hardwarefehler an Client zurückmelden

configs/server.json

@@ -3,6 +3,9 @@
         "address": "0.0.0.0",
         "port": 5000
     },
+
+    "hardware_error_response": "ERROR - HARDWARE NOT AVAILABLE",
+
     "devices": [
         {
             "id": "radio",

internal/client/integration_test.go

@@ -29,6 +29,16 @@ import (
 	"git.lang-dieter.de/rs2322tcp/internal/server"
 )
 
+///////////////////////////////////////////////////////////////////////////////
+// Test configuration
+///////////////////////////////////////////////////////////////////////////////
+
+const testHardwareErrorResponse = "TEST ERROR RESPONSE"
+
+///////////////////////////////////////////////////////////////////////////////
+// Virtual serial pair
+///////////////////////////////////////////////////////////////////////////////
+
 func startVirtualSerialPair(t *testing.T) (string, string, func()) {
 	t.Helper()
 
@@ -79,6 +89,10 @@ func startVirtualSerialPair(t *testing.T) (string, string, func()) {
 	}
 }
 
+///////////////////////////////////////////////////////////////////////////////
+// Read helper
+///////////////////////////////////////////////////////////////////////////////
+
 func readExactWithTimeout(
 	t *testing.T,
 	reader io.Reader,
@@ -105,6 +119,10 @@ func readExactWithTimeout(
 	}
 }
 
+///////////////////////////////////////////////////////////////////////////////
+// Integration test
+///////////////////////////////////////////////////////////////////////////////
+
 func TestClientServerSerialIntegration(t *testing.T) {
 	serialA, serialB, cleanup := startVirtualSerialPair(t)
 	defer cleanup()
@@ -130,6 +148,7 @@ func TestClientServerSerialIntegration(t *testing.T) {
 			Address: "127.0.0.1",
 			Port:    controlPort,
 		},
+		HardwareErrorResponse: testHardwareErrorResponse,
 		Devices: []config.DeviceConfig{
 			{
 				ID:         "radio",

internal/client/runtime_integration_test.go

@@ -82,6 +82,7 @@ func TestClientRuntimeSerialIntegration(t *testing.T) {
 			Address: "127.0.0.1",
 			Port:    controlPort,
 		},
+		HardwareErrorResponse: testHardwareErrorResponse,
 		Devices: []config.DeviceConfig{
 			{
 				ID:         "radio",

internal/config/config.go

@@ -23,8 +23,9 @@ import (
 
 // ServerConfig contains the complete server configuration.
 type ServerConfig struct {
-	Listen  ListenConfig   `json:"listen"`
-	Devices []DeviceConfig `json:"devices"`
+	Listen                ListenConfig   `json:"listen"`
+	HardwareErrorResponse string         `json:"hardware_error_response"`
+	Devices               []DeviceConfig `json:"devices"`
 }
 
 // ListenConfig contains the network listener configuration.
@@ -88,6 +89,9 @@ const (
 	// DefaultVirtualPortLast is the last virtual USB serial port number
 	// used when no virtual port range is specified.
 	DefaultVirtualPortLast = 199
+
+	// Fehlermeldung wenn Hardware nicht erreichbar ist
+	DefaultHardwareErrorResponse = "ERROR - HARDWARE NOT AVAILABLE"
 )
 
 // DefaultVirtualPortRange returns the default virtual port range.
@@ -110,6 +114,10 @@ func LoadServer(filename string) (*ServerConfig, error) {
 		return nil, err
 	}
 
+	if cfg.HardwareErrorResponse == "" {
+		cfg.HardwareErrorResponse = DefaultHardwareErrorResponse
+	}
+
 	if err := cfg.Validate(); err != nil {
 		return nil, err
 	}

internal/config/config_test.go

@@ -50,6 +50,14 @@ func TestLoadServer(t *testing.T) {
 		t.Fatalf("LoadServer() failed: %v", err)
 	}
 
+	if cfg.HardwareErrorResponse != config.DefaultHardwareErrorResponse {
+		t.Errorf(
+			"HardwareErrorResponse = %q, want %q",
+			cfg.HardwareErrorResponse,
+			config.DefaultHardwareErrorResponse,
+		)
+	}
+
 	if cfg.Listen.Address != "0.0.0.0" {
 		t.Errorf("Listen.Address = %q, want %q",
 			cfg.Listen.Address, "0.0.0.0")

internal/serial/serial.go

@@ -16,6 +16,7 @@ package serial
 import (
 	"fmt"
 	"io"
+	"sync"
 
 	bugserial "go.bug.st/serial"
 
@@ -28,6 +29,7 @@ import (
 
 // Connection represents an opened serial connection.
 type Connection struct {
+	mu   sync.Mutex
 	port bugserial.Port
 }
 
@@ -126,20 +128,36 @@ func createMode(device config.DeviceConfig) (*bugserial.Mode, error) {
 
 // Read reads data from the serial connection.
 func (c *Connection) Read(p []byte) (int, error) {
-	if c == nil || c.port == nil {
+	if c == nil {
 		return 0, io.ErrClosedPipe
 	}
 
-	return c.port.Read(p)
+	c.mu.Lock()
+	port := c.port
+	c.mu.Unlock()
+
+	if port == nil {
+		return 0, io.ErrClosedPipe
+	}
+
+	return port.Read(p)
 }
 
 // Write writes data to the serial connection.
 func (c *Connection) Write(p []byte) (int, error) {
-	if c == nil || c.port == nil {
+	if c == nil {
 		return 0, io.ErrClosedPipe
 	}
 
-	return c.port.Write(p)
+	c.mu.Lock()
+	port := c.port
+	c.mu.Unlock()
+
+	if port == nil {
+		return 0, io.ErrClosedPipe
+	}
+
+	return port.Write(p)
 }
 
 ///////////////////////////////////////////////////////////////////////////////
@@ -148,12 +166,21 @@ func (c *Connection) Write(p []byte) (int, error) {
 
 // Close closes the serial connection.
 func (c *Connection) Close() error {
-	if c == nil || c.port == nil {
+	if c == nil {
 		return nil
 	}
 
-	err := c.port.Close()
+	c.mu.Lock()
+
+	if c.port == nil {
+		c.mu.Unlock()
+		return nil
+	}
+
+	port := c.port
 	c.port = nil
 
-	return err
+	c.mu.Unlock()
+
+	return port.Close()
 }

internal/server/control.go

@@ -336,6 +336,7 @@ func (s *ControlServer) runDataListener(
 		dataConnection, err := NewDataConnection(
 			tcpConn,
 			serialConn,
+			s.config.HardwareErrorResponse,
 		)
 		if err != nil {
 			log.Printf(

internal/server/control_test.go

@@ -40,6 +40,7 @@ func testServerConfig() *config.ServerConfig {
 			Address: "127.0.0.1",
 			Port:    5000,
 		},
+		HardwareErrorResponse: testHardwareErrorResponse,
 		Devices: []config.DeviceConfig{
 			{
 				ID:         "radio",
@@ -451,6 +452,7 @@ func TestControlServerDataConnection(t *testing.T) {
 			Address: "127.0.0.1",
 			Port:    5000,
 		},
+		HardwareErrorResponse: testHardwareErrorResponse,
 		Devices: []config.DeviceConfig{
 			{
 				ID:         "radio",

internal/server/data_connection.go

@@ -1,7 +1,7 @@
 /*
  * ============================================================================
  * Projekt.....: rs2322tcp
- * Datei.......: data_connection.go
+ * Datei.......: internal/server/data_connection.go
  * Copyright (C) 2026 Dieter Lang
  *
  * SPDX-License-Identifier: GPL-3.0-or-later
@@ -31,12 +31,17 @@ import (
 //	TCP  ->  Serial
 //	TCP  <-  Serial
 //
+// If writing TCP data to the serial device fails, the configured hardware
+// error response is sent back over the TCP connection before the connection
+// is terminated.
+//
 // The serial side is represented by an io.ReadWriteCloser so that this
 // server component does not depend directly on the concrete serial
 // implementation.
 type DataConnection struct {
-	tcp    net.Conn
-	serial io.ReadWriteCloser
+	tcp                   net.Conn
+	serial                io.ReadWriteCloser
+	hardwareErrorResponse string
 
 	closeOnce sync.Once
 	closeErr  error
@@ -50,6 +55,7 @@ type DataConnection struct {
 func NewDataConnection(
 	tcp net.Conn,
 	serial io.ReadWriteCloser,
+	hardwareErrorResponse string,
 ) (*DataConnection, error) {
 	if tcp == nil {
 		return nil, fmt.Errorf("TCP connection is nil")
@@ -59,9 +65,14 @@ func NewDataConnection(
 		return nil, fmt.Errorf("serial connection is nil")
 	}
 
+	if hardwareErrorResponse == "" {
+		return nil, fmt.Errorf("hardware error response is empty")
+	}
+
 	return &DataConnection{
-		tcp:    tcp,
-		serial: serial,
+		tcp:                   tcp,
+		serial:                serial,
+		hardwareErrorResponse: hardwareErrorResponse,
 	}, nil
 }
 
@@ -87,6 +98,54 @@ func (c *DataConnection) SerialConn() io.ReadWriteCloser {
 	return c.serial
 }
 
+///////////////////////////////////////////////////////////////////////////////
+// Data transfer
+///////////////////////////////////////////////////////////////////////////////
+
+// copyTCPToSerial transfers data from the TCP connection to the serial
+// device.
+//
+// If writing to the serial device fails, the configured hardware error
+// response is sent back to the TCP client before the transfer terminates.
+func (c *DataConnection) copyTCPToSerial() error {
+	if c == nil {
+		return fmt.Errorf("data connection is nil")
+	}
+
+	buffer := make([]byte, 32*1024)
+
+	for {
+		n, err := c.tcp.Read(buffer)
+
+		if n > 0 {
+			if _, writeErr := c.serial.Write(buffer[:n]); writeErr != nil {
+				_, _ = io.WriteString(
+					c.tcp,
+					c.hardwareErrorResponse,
+				)
+
+				return writeErr
+			}
+		}
+
+		if err != nil {
+			return err
+		}
+	}
+}
+
+// copySerialToTCP transfers data from the serial device to the TCP
+// connection.
+func (c *DataConnection) copySerialToTCP() error {
+	if c == nil {
+		return fmt.Errorf("data connection is nil")
+	}
+
+	_, err := io.Copy(c.tcp, c.serial)
+
+	return err
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 // Run
 ///////////////////////////////////////////////////////////////////////////////
@@ -96,6 +155,10 @@ func (c *DataConnection) SerialConn() io.ReadWriteCloser {
 // Run blocks until one of the two transfer directions terminates.
 // The other direction is then stopped and both connections are closed.
 //
+// If writing data from TCP to the serial device fails, the configured
+// hardware error response is sent to the TCP client before the connection
+// is closed.
+//
 // The first non-EOF transfer error is returned.
 func (c *DataConnection) Run() error {
 	if c == nil {
@@ -111,15 +174,13 @@ func (c *DataConnection) Run() error {
 	go func() {
 		defer wg.Done()
 
-		_, err := io.Copy(c.serial, c.tcp)
-		errCh <- err
+		errCh <- c.copyTCPToSerial()
 	}()
 
 	go func() {
 		defer wg.Done()
 
-		_, err := io.Copy(c.tcp, c.serial)
-		errCh <- err
+		errCh <- c.copySerialToTCP()
 	}()
 
 	err := <-errCh

internal/server/data_connection_test.go

@@ -14,6 +14,7 @@ package server_test
 
 import (
 	"bytes"
+	"errors"
 	"io"
 	"net"
 	"sync"
@@ -31,6 +32,8 @@ type testSerialConnection struct {
 	reader *bytes.Reader
 	writer bytes.Buffer
 
+	writeErr error
+
 	mu     sync.Mutex
 	closed bool
 
@@ -45,6 +48,14 @@ func newTestSerialConnection(data []byte) *testSerialConnection {
 	}
 }
 
+func newFailingTestSerialConnection(writeErr error) *testSerialConnection {
+	return &testSerialConnection{
+		reader:   bytes.NewReader(nil),
+		writeErr: writeErr,
+		closeCh:  make(chan struct{}),
+	}
+}
+
 func (s *testSerialConnection) Read(p []byte) (int, error) {
 	s.mu.Lock()
 
@@ -76,6 +87,10 @@ func (s *testSerialConnection) Write(p []byte) (int, error) {
 		return 0, io.ErrClosedPipe
 	}
 
+	if s.writeErr != nil {
+		return 0, s.writeErr
+	}
+
 	return s.writer.Write(p)
 }
 
@@ -116,6 +131,7 @@ func TestNewDataConnection(t *testing.T) {
 	connection, err := server.NewDataConnection(
 		tcpServer,
 		serial,
+		testHardwareErrorResponse,
 	)
 	if err != nil {
 		t.Fatalf("NewDataConnection() failed: %v", err)
@@ -136,6 +152,7 @@ func TestNewDataConnectionRejectsNilTCP(t *testing.T) {
 	connection, err := server.NewDataConnection(
 		nil,
 		serial,
+		testHardwareErrorResponse,
 	)
 
 	if err == nil {
@@ -155,6 +172,7 @@ func TestNewDataConnectionRejectsNilSerial(t *testing.T) {
 	connection, err := server.NewDataConnection(
 		tcpServer,
 		nil,
+		testHardwareErrorResponse,
 	)
 
 	if err == nil {
@@ -179,6 +197,7 @@ func TestDataConnectionTCPToSerial(t *testing.T) {
 	connection, err := server.NewDataConnection(
 		tcpServer,
 		serial,
+		testHardwareErrorResponse,
 	)
 	if err != nil {
 		t.Fatalf("NewDataConnection() failed: %v", err)
@@ -223,6 +242,60 @@ func TestDataConnectionTCPToSerial(t *testing.T) {
 	}
 }
 
+///////////////////////////////////////////////////////////////////////////////
+// TCP -> Serial error
+///////////////////////////////////////////////////////////////////////////////
+
+func TestDataConnectionTCPToSerialWriteError(t *testing.T) {
+	tcpServer, tcpClient := net.Pipe()
+	defer tcpClient.Close()
+
+	writeErr := errors.New("hardware write failed")
+
+	serial := newFailingTestSerialConnection(writeErr)
+
+	connection, err := server.NewDataConnection(
+		tcpServer,
+		serial,
+		testHardwareErrorResponse,
+	)
+	if err != nil {
+		t.Fatalf("NewDataConnection() failed: %v", err)
+	}
+
+	done := make(chan error, 1)
+
+	go func() {
+		done <- connection.Run()
+	}()
+
+	testData := []byte("hello unavailable hardware")
+
+	if _, err := tcpClient.Write(testData); err != nil {
+		t.Fatalf("TCP Write() failed: %v", err)
+	}
+
+	errorResponse := make([]byte, len(testHardwareErrorResponse))
+
+	if _, err := io.ReadFull(tcpClient, errorResponse); err != nil {
+		t.Fatalf("TCP Read() failed: %v", err)
+	}
+
+	if string(errorResponse) != testHardwareErrorResponse {
+		t.Fatalf(
+			"error response = %q, want %q",
+			string(errorResponse),
+			testHardwareErrorResponse,
+		)
+	}
+
+	select {
+	case <-done:
+	case <-time.After(time.Second):
+		t.Fatal("DataConnection.Run() did not terminate")
+	}
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 // Serial -> TCP
 ///////////////////////////////////////////////////////////////////////////////
@@ -238,6 +311,7 @@ func TestDataConnectionSerialToTCP(t *testing.T) {
 	connection, err := server.NewDataConnection(
 		tcpServer,
 		serial,
+		testHardwareErrorResponse,
 	)
 	if err != nil {
 		t.Fatalf("NewDataConnection() failed: %v", err)
@@ -285,6 +359,7 @@ func TestDataConnectionClose(t *testing.T) {
 	connection, err := server.NewDataConnection(
 		tcpServer,
 		serial,
+		testHardwareErrorResponse,
 	)
 	if err != nil {
 		t.Fatalf("NewDataConnection() failed: %v", err)

internal/server/data_handler.go

@@ -38,8 +38,9 @@ type SerialFactory func() (io.ReadWriteCloser, error)
 // DataHandler accepts TCP data connections and connects them to a serial
 // device.
 type DataHandler struct {
-	listener      *DataListener
-	serialFactory SerialFactory
+	listener              *DataListener
+	serialFactory         SerialFactory
+	hardwareErrorResponse string
 }
 
 ///////////////////////////////////////////////////////////////////////////////
@@ -53,6 +54,7 @@ type DataHandler struct {
 func NewDataHandler(
 	listener *DataListener,
 	serialFactory SerialFactory,
+	hardwareErrorResponse string,
 ) (*DataHandler, error) {
 	if listener == nil {
 		return nil, fmt.Errorf("data listener is nil")
@@ -62,9 +64,14 @@ func NewDataHandler(
 		return nil, fmt.Errorf("serial factory is nil")
 	}
 
+	if hardwareErrorResponse == "" {
+		return nil, fmt.Errorf("hardware error response is empty")
+	}
+
 	return &DataHandler{
-		listener:      listener,
-		serialFactory: serialFactory,
+		listener:              listener,
+		serialFactory:         serialFactory,
+		hardwareErrorResponse: hardwareErrorResponse,
 	}, nil
 }
 
@@ -114,6 +121,7 @@ func (h *DataHandler) handleConnection(tcpConn net.Conn) {
 	dataConnection, err := NewDataConnection(
 		tcpConn,
 		serialConn,
+		h.hardwareErrorResponse,
 	)
 	if err != nil {
 		log.Printf("create data connection: %v", err)

internal/server/data_handler_test.go

@@ -24,6 +24,12 @@ import (
 	"git.lang-dieter.de/rs2322tcp/internal/server"
 )
 
+///////////////////////////////////////////////////////////////////////////////
+// Test constants
+///////////////////////////////////////////////////////////////////////////////
+
+const testHardwareErrorResponse = "TEST ERROR RESPONSE"
+
 ///////////////////////////////////////////////////////////////////////////////
 // Test serial connection
 ///////////////////////////////////////////////////////////////////////////////
@@ -119,6 +125,7 @@ func TestNewDataHandler(t *testing.T) {
 		func() (io.ReadWriteCloser, error) {
 			return serial, nil
 		},
+		testHardwareErrorResponse,
 	)
 	if err != nil {
 		t.Fatalf("NewDataHandler() failed: %v", err)
@@ -135,6 +142,7 @@ func TestNewDataHandlerRejectsNilListener(t *testing.T) {
 		func() (io.ReadWriteCloser, error) {
 			return newHandlerTestSerial(nil), nil
 		},
+		testHardwareErrorResponse,
 	)
 
 	if err == nil {
@@ -156,6 +164,7 @@ func TestNewDataHandlerRejectsNilFactory(t *testing.T) {
 	handler, err := server.NewDataHandler(
 		listener,
 		nil,
+		testHardwareErrorResponse,
 	)
 
 	if err == nil {
@@ -185,6 +194,7 @@ func TestDataHandlerTCPToSerial(t *testing.T) {
 		func() (io.ReadWriteCloser, error) {
 			return serial, nil
 		},
+		testHardwareErrorResponse,
 	)
 	if err != nil {
 		t.Fatalf("NewDataHandler() failed: %v", err)
@@ -255,6 +265,7 @@ func TestDataHandlerSerialToTCP(t *testing.T) {
 		func() (io.ReadWriteCloser, error) {
 			return serial, nil
 		},
+		testHardwareErrorResponse,
 	)
 	if err != nil {
 		t.Fatalf("NewDataHandler() failed: %v", err)
@@ -311,6 +322,7 @@ func TestDataHandlerSerialFactoryError(t *testing.T) {
 		func() (io.ReadWriteCloser, error) {
 			return nil, io.ErrClosedPipe
 		},
+		testHardwareErrorResponse,
 	)
 	if err != nil {
 		t.Fatalf("NewDataHandler() failed: %v", err)