Implement client control and data connections

CHANGELOG.md

@@ -20,6 +20,13 @@ Alle wesentlichen Änderungen am Projekt werden in dieser Datei dokumentiert.
 - Integrationstest mit virtuellen seriellen Schnittstellen über `socat`
 - Tests für TCP → RS232 und RS232 → TCP
 - Tests für Session-Reconnect und Ressourcenverwaltung
+- Client-Control-Verbindung unter `internal/client`
+- Clientseitige Verarbeitung von `HELLO`
+- Clientseitige Abfrage der konfigurierten Geräte über `GET_DEVICES`
+- Clientseitige Verarbeitung der vom Server gelieferten Geräteinformationen einschließlich dynamischem Data-Port
+- Clientseitiger Aufbau der TCP-Data-Verbindung
+- Integrationstest für die vollständige Client-/Server-Kommunikation
+- End-to-End-Test der TCP-/RS232-Datenübertragung in beide Richtungen
 
 ### Changed
 
@@ -36,33 +43,55 @@ Alle wesentlichen Änderungen am Projekt werden in dieser Datei dokumentiert.
 - `go test ./...` erfolgreich
 - `go test -race ./...` erfolgreich
 - Race Condition im `DataListener` erkannt und behoben
+- Client-/Server-Integrationstest erfolgreich
+- Race-Test des Client-/Server-Integrationstests erfolgreich
 
 ### Status
 
-Die grundlegende Server-seitige TCP-/RS232-Datenübertragung ist implementiert und durch automatisierte Tests abgesichert.
+Die grundlegende TCP-/RS232-Datenübertragung ist serverseitig implementiert und der Client kann inzwischen die Control-Verbindung sowie die zugehörige Data-Verbindung aufbauen.
 
-Der Datenpfad ist derzeit:
+Der aktuelle Datenpfad ist:
 
 ```text
-TCP-Control-Verbindung
+Client
-        │
+   │
-        ▼
+   ├── TCP-Control-Verbindung
-     Session
+   │        │
-        │
+   │        ▼
-        ▼
+   │     Session
- dynamischer Data-Port
+   │        │
-        │
+   │        ▼
-        ▼
+   │   GET_DEVICES
- TCP-Data-Verbindung
+   │        │
-        │
+   │        ▼
-        ▼
+   │   Geräteinformationen
- internal/serial
+   │        │
-        │
+   │        ▼
-        ▼
+   │  dynamischer Data-Port
-   RS232-Gerät
+   │        │
+   └── TCP-Data-Verbindung
+            │
+            ▼
+        DataListener
+            │
+            ▼
+       DataConnection
+            │
+            ▼
+       internal/serial
+            │
+            ▼
+         RS232-Gerät
 ```
 
-Die Client-seitige Bereitstellung einer virtuellen seriellen Schnittstelle ist noch nicht implementiert.
+Die Datenübertragung wurde bereits in beide Richtungen erfolgreich getestet:
+
+```text
+TCP → RS232
+RS232 → TCP
+```
+
+Die clientseitige Bereitstellung einer virtuellen seriellen Schnittstelle für die vorhandene Hersteller-Software ist noch nicht implementiert.
 
 ---
 

README.md

@@ -40,28 +40,40 @@ rs2322tcp-client                             │
                                Funkgerät              Rotor
 ```
 
-## Aktueller Server-Datenpfad
+## Aktueller Datenpfad
 
-Die serverseitige TCP-/RS232-Verbindung ist inzwischen implementiert:
+Die serverseitige TCP-/RS232-Verbindung sowie die grundlegende Client-Control- und Client-Data-Kommunikation sind inzwischen implementiert:
 
 ```text
-TCP-Control
+Client
-     │
+   │
-     ▼
+   ├── TCP-Control
-  Session
+   │      │
-     │
+   │      ▼
-     ├── Gerät 1 ──► dynamischer Data-Port
+   │    Session
-     │                    │
+   │      │
-     │                    ▼
+   │      ▼
-     │               TCP Data
+   │   GET_DEVICES
-     │                    │
+   │      │
-     │                    ▼
+   │      ▼
-     │              Serial Layer
+   │   Geräteinformationen
-     │                    │
+   │      │
-     │                    ▼
+   │      ▼
-     │                 RS232
+   │   dynamischer Data-Port
-     │
+   │
-     └── Gerät 2 ──► dynamischer Data-Port
+   └── TCP-Data
+          │
+          ▼
+      DataListener
+          │
+          ▼
+      DataConnection
+          │
+          ▼
+      Serial Layer
+          │
+          ▼
+        RS232
 ```
 
 Die serielle Schnittstelle wird erst geöffnet, wenn ein Client tatsächlich eine Data-Verbindung zum entsprechenden dynamischen TCP-Port aufbaut.
@@ -75,6 +87,8 @@ TCP ───────────────► RS232
 TCP ◄────────────── RS232
 ```
 
+Der komplette Client-/Server-Datenpfad wird inzwischen durch einen Integrationstest mit virtuellen seriellen Schnittstellen geprüft.
+
 ## Client
 
 Der Client soll gleichberechtigt unter folgenden Betriebssystemen eingesetzt werden können:
@@ -84,7 +98,15 @@ Der Client soll gleichberechtigt unter folgenden Betriebssystemen eingesetzt wer
 
 Die plattformspezifische Bereitstellung der virtuellen seriellen Schnittstelle wird vom gemeinsamen Client-Kern getrennt.
 
-Die Client-seitige virtuelle serielle Schnittstelle ist derzeit noch nicht implementiert.
+Der gemeinsame Client-Kern kann inzwischen:
+
+- die Control-Verbindung zum Server aufbauen
+- den Control-Handshake durchführen
+- die konfigurierten Geräte vom Server abfragen
+- den vom Server gelieferten dynamischen Data-Port verwenden
+- die TCP-Data-Verbindung zum Server aufbauen
+
+Die clientseitige virtuelle serielle Schnittstelle ist derzeit noch nicht implementiert.
 
 ## Server
 
@@ -172,6 +194,8 @@ TCP → RS232
 RS232 → TCP
 ```
 
+Zusätzlich wird die vollständige Client-/Server-Kommunikation über den echten `ControlServer`-Lifecycle (`Listen()` / `Serve()`) getestet.
+
 ## Projektstruktur
 
 ```text
@@ -232,18 +256,23 @@ Release-Versionen werden über Git-Tags gekennzeichnet.
 
 Das Projekt befindet sich weiterhin in der frühen Entwicklungsphase.
 
-Die ursprüngliche Projektgrundlage aus Version `0.0.1` wurde inzwischen um eine funktionierende serverseitige TCP-/RS232-Datenübertragung erweitert.
+Die ursprüngliche Projektgrundlage aus Version `0.0.1` wurde inzwischen um eine funktionierende serverseitige TCP-/RS232-Datenübertragung und die grundlegende Client-Control-/Data-Kommunikation erweitert.
 
 Implementiert und getestet sind derzeit:
 
 - Server-Control-Verbindung
+- Client-Control-Verbindung
+- `HELLO`-Handshake
+- `GET_DEVICES`
 - Session-Verwaltung
 - dynamische Data-Ports
+- Clientseitiger Aufbau der Data-Verbindung
 - DataConnection
 - bidirektionale TCP-/RS232-Datenübertragung
 - Serial-Abstraktion
 - Konfiguration der seriellen Parameter
 - virtuelle serielle Integrationstests
+- Client-/Server-End-to-End-Integrationstest
 - nebenläufigkeitssichere Data-Listener
 - Race-Detection
 

internal/client/control.go

@@ -0,0 +1,172 @@
+/*
+ * ============================================================================
+ * Projekt.....: rs2322tcp
+ * Datei.......: control.go
+ * Copyright (C) 2026 Dieter Lang
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ * Beschreibung:
+ * Client-seitige Control-Verbindung zum rs2322tcp-Server.
+ * Baut die TCP-Control-Verbindung auf, führt den Protokoll-Handshake durch
+ * und liest die vom Server bereitgestellten Geräteinformationen.
+ * ============================================================================
+ */
+package client
+
+import (
+	"bufio"
+	"fmt"
+	"net"
+
+	"git.lang-dieter.de/rs2322tcp/internal/transport"
+)
+
+///////////////////////////////////////////////////////////////////////////////
+// Client
+///////////////////////////////////////////////////////////////////////////////
+
+// Client represents a connection to an rs2322tcp server.
+type Client struct {
+	conn   net.Conn
+	reader *bufio.Reader
+}
+
+///////////////////////////////////////////////////////////////////////////////
+// Constructor
+///////////////////////////////////////////////////////////////////////////////
+
+// New creates a new client and connects to the specified server address.
+//
+// The address must be in the form "host:port".
+func New(address string) (*Client, error) {
+	if address == "" {
+		return nil, fmt.Errorf("server address is empty")
+	}
+
+	conn, err := net.Dial("tcp", address)
+	if err != nil {
+		return nil, fmt.Errorf(
+			"connect to server %q: %w",
+			address,
+			err,
+		)
+	}
+
+	client := &Client{
+		conn:   conn,
+		reader: bufio.NewReader(conn),
+	}
+
+	if err := client.hello(); err != nil {
+		_ = conn.Close()
+
+		return nil, err
+	}
+
+	return client, nil
+}
+
+///////////////////////////////////////////////////////////////////////////////
+// Properties
+///////////////////////////////////////////////////////////////////////////////
+
+// Conn returns the underlying control connection.
+//
+// It returns nil if the client is nil or has already been closed.
+func (c *Client) Conn() net.Conn {
+	if c == nil {
+		return nil
+	}
+
+	return c.conn
+}
+
+///////////////////////////////////////////////////////////////////////////////
+// Handshake
+///////////////////////////////////////////////////////////////////////////////
+
+func (c *Client) hello() error {
+	if c == nil || c.conn == nil {
+		return fmt.Errorf("client is not connected")
+	}
+
+	if err := transport.WriteMessage(
+		c.conn,
+		transport.NewHello(),
+	); err != nil {
+		return fmt.Errorf("send hello: %w", err)
+	}
+
+	var response transport.HelloResponseMessage
+
+	if err := transport.ReadMessage(
+		c.reader,
+		&response,
+	); err != nil {
+		return fmt.Errorf("read hello response: %w", err)
+	}
+
+	if response.Type != transport.MessageHelloResponse {
+		return fmt.Errorf(
+			"unexpected hello response: %q",
+			response.Type,
+		)
+	}
+
+	return nil
+}
+
+///////////////////////////////////////////////////////////////////////////////
+// Devices
+///////////////////////////////////////////////////////////////////////////////
+
+// GetDevices requests the configured remote devices from the server.
+//
+// The returned list contains the session-specific dynamic TCP data ports.
+func (c *Client) GetDevices() ([]transport.RemoteDeviceInfo, error) {
+	if c == nil || c.conn == nil {
+		return nil, fmt.Errorf("client is not connected")
+	}
+
+	if err := transport.WriteMessage(
+		c.conn,
+		transport.NewGetDevices(),
+	); err != nil {
+		return nil, fmt.Errorf("send get-devices request: %w", err)
+	}
+
+	var response transport.DeviceListMessage
+
+	if err := transport.ReadMessage(
+		c.reader,
+		&response,
+	); err != nil {
+		return nil, fmt.Errorf("read device list: %w", err)
+	}
+
+	if response.Type != transport.MessageDeviceList {
+		return nil, fmt.Errorf(
+			"unexpected device list response: %q",
+			response.Type,
+		)
+	}
+
+	return response.Devices, nil
+}
+
+///////////////////////////////////////////////////////////////////////////////
+// Close
+///////////////////////////////////////////////////////////////////////////////
+
+// Close closes the client control connection.
+func (c *Client) Close() error {
+	if c == nil || c.conn == nil {
+		return nil
+	}
+
+	err := c.conn.Close()
+	c.conn = nil
+
+	return err
+}

internal/client/control_test.go

@@ -0,0 +1,168 @@
+package client_test
+
+import (
+	"bufio"
+	"net"
+	"testing"
+
+	"git.lang-dieter.de/rs2322tcp/internal/client"
+	"git.lang-dieter.de/rs2322tcp/internal/transport"
+)
+
+func startTestServer(t *testing.T, handler func(net.Conn)) string {
+	t.Helper()
+
+	listener, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("listen failed: %v", err)
+	}
+
+	t.Cleanup(func() {
+		_ = listener.Close()
+	})
+
+	go func() {
+		conn, err := listener.Accept()
+		if err != nil {
+			return
+		}
+
+		handler(conn)
+	}()
+
+	return listener.Addr().String()
+}
+
+func TestClientHello(t *testing.T) {
+	address := startTestServer(t, func(conn net.Conn) {
+		defer conn.Close()
+
+		reader := bufio.NewReader(conn)
+
+		var hello transport.HelloMessage
+
+		if err := transport.ReadMessage(reader, &hello); err != nil {
+			return
+		}
+
+		if hello.Type != transport.MessageHello {
+			return
+		}
+
+		_ = transport.WriteMessage(
+			conn,
+			transport.NewHelloResponse(),
+		)
+	})
+
+	c, err := client.New(address)
+	if err != nil {
+		t.Fatalf("client.New() failed: %v", err)
+	}
+	defer c.Close()
+}
+
+func TestClientGetDevices(t *testing.T) {
+	address := startTestServer(t, func(conn net.Conn) {
+		defer conn.Close()
+
+		reader := bufio.NewReader(conn)
+
+		// HELLO
+		var hello transport.HelloMessage
+
+		if err := transport.ReadMessage(reader, &hello); err != nil {
+			return
+		}
+
+		if hello.Type != transport.MessageHello {
+			return
+		}
+
+		if err := transport.WriteMessage(
+			conn,
+			transport.NewHelloResponse(),
+		); err != nil {
+			return
+		}
+
+		// GET_DEVICES
+		var request transport.GetDevicesMessage
+
+		if err := transport.ReadMessage(reader, &request); err != nil {
+			return
+		}
+
+		if request.Type != transport.MessageGetDevices {
+			return
+		}
+
+		response := transport.NewDeviceList([]transport.RemoteDeviceInfo{
+			{
+				ID:       "radio",
+				Name:     "Funkgerät",
+				DataPort: 4711,
+				BaudRate: 9600,
+				DataBits: 8,
+				Parity:   "none",
+				StopBits: 1,
+			},
+			{
+				ID:       "rotor",
+				Name:     "Antennenrotor",
+				DataPort: 4712,
+				BaudRate: 4800,
+				DataBits: 8,
+				Parity:   "none",
+				StopBits: 1,
+			},
+		})
+
+		_ = transport.WriteMessage(conn, response)
+	})
+
+	c, err := client.New(address)
+	if err != nil {
+		t.Fatalf("client.New() failed: %v", err)
+	}
+	defer c.Close()
+
+	devices, err := c.GetDevices()
+	if err != nil {
+		t.Fatalf("GetDevices() failed: %v", err)
+	}
+
+	if len(devices) != 2 {
+		t.Fatalf("len(devices) = %d, want 2", len(devices))
+	}
+
+	if devices[0].ID != "radio" {
+		t.Errorf(
+			"devices[0].ID = %q, want %q",
+			devices[0].ID,
+			"radio",
+		)
+	}
+
+	if devices[0].DataPort != 4711 {
+		t.Errorf(
+			"devices[0].DataPort = %d, want 4711",
+			devices[0].DataPort,
+		)
+	}
+
+	if devices[1].ID != "rotor" {
+		t.Errorf(
+			"devices[1].ID = %q, want %q",
+			devices[1].ID,
+			"rotor",
+		)
+	}
+
+	if devices[1].DataPort != 4712 {
+		t.Errorf(
+			"devices[1].DataPort = %d, want 4712",
+			devices[1].DataPort,
+		)
+	}
+}

internal/client/data.go

@@ -0,0 +1,62 @@
+package client
+
+import (
+	"fmt"
+	"net"
+
+	"git.lang-dieter.de/rs2322tcp/internal/transport"
+)
+
+///////////////////////////////////////////////////////////////////////////////
+// Data connection
+///////////////////////////////////////////////////////////////////////////////
+
+// OpenDataConnection opens the TCP data connection for the specified
+// remote device.
+//
+// The DataPort is supplied by the server as part of the device information.
+func (c *Client) OpenDataConnection(
+	device transport.RemoteDeviceInfo,
+) (net.Conn, error) {
+	if c == nil || c.conn == nil {
+		return nil, fmt.Errorf("client is not connected")
+	}
+
+	if device.DataPort == 0 {
+		return nil, fmt.Errorf(
+			"device %q has no data port",
+			device.ID,
+		)
+	}
+
+	serverAddr := c.conn.RemoteAddr()
+	if serverAddr == nil {
+		return nil, fmt.Errorf("control connection has no remote address")
+	}
+
+	host, _, err := net.SplitHostPort(serverAddr.String())
+	if err != nil {
+		return nil, fmt.Errorf(
+			"invalid control server address %q: %w",
+			serverAddr.String(),
+			err,
+		)
+	}
+
+	dataAddr := net.JoinHostPort(
+		host,
+		fmt.Sprintf("%d", device.DataPort),
+	)
+
+	conn, err := net.Dial("tcp", dataAddr)
+	if err != nil {
+		return nil, fmt.Errorf(
+			"connect data port %d for device %q: %w",
+			device.DataPort,
+			device.ID,
+			err,
+		)
+	}
+
+	return conn, nil
+}

internal/client/data_test.go

@@ -0,0 +1,120 @@
+package client_test
+
+import (
+	"bufio"
+	"net"
+	"testing"
+
+	"git.lang-dieter.de/rs2322tcp/internal/client"
+	"git.lang-dieter.de/rs2322tcp/internal/transport"
+)
+
+func TestClientOpenDataConnection(t *testing.T) {
+	dataListener, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("data listener failed: %v", err)
+	}
+	defer dataListener.Close()
+
+	dataPort := dataListener.Addr().(*net.TCPAddr).Port
+
+	controlListener, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("control listener failed: %v", err)
+	}
+	defer controlListener.Close()
+
+	serverDone := make(chan error, 1)
+
+	go func() {
+		conn, err := controlListener.Accept()
+		if err != nil {
+			serverDone <- err
+			return
+		}
+		defer conn.Close()
+
+		reader := bufio.NewReader(conn)
+
+		var hello transport.HelloMessage
+
+		if err := transport.ReadMessage(reader, &hello); err != nil {
+			serverDone <- err
+			return
+		}
+
+		if hello.Type != transport.MessageHello {
+			serverDone <- &testError{
+				message: "unexpected hello message type",
+			}
+			return
+		}
+
+		if err := transport.WriteMessage(
+			conn,
+			transport.NewHelloResponse(),
+		); err != nil {
+			serverDone <- err
+			return
+		}
+
+		serverDone <- nil
+	}()
+
+	clientConn, err := client.New(controlListener.Addr().String())
+	if err != nil {
+		t.Fatalf("client.New() failed: %v", err)
+	}
+	defer clientConn.Close()
+
+	device := transport.RemoteDeviceInfo{
+		ID:       "radio",
+		Name:     "Funkgerät",
+		DataPort: dataPort,
+	}
+
+	dataConn, err := clientConn.OpenDataConnection(device)
+	if err != nil {
+		t.Fatalf("OpenDataConnection() failed: %v", err)
+	}
+	defer dataConn.Close()
+
+	serverDataConn, err := dataListener.Accept()
+	if err != nil {
+		t.Fatalf("data listener Accept() failed: %v", err)
+	}
+	defer serverDataConn.Close()
+
+	if err := <-serverDone; err != nil {
+		t.Fatalf("control server failed: %v", err)
+	}
+
+	// Verify that the data connection is actually usable.
+	message := []byte("test")
+
+	if _, err := dataConn.Write(message); err != nil {
+		t.Fatalf("data connection Write() failed: %v", err)
+	}
+
+	buffer := make([]byte, len(message))
+
+	if _, err := serverDataConn.Read(buffer); err != nil {
+		t.Fatalf("data connection Read() failed: %v", err)
+	}
+
+	if string(buffer) != string(message) {
+		t.Fatalf(
+			"received %q, want %q",
+			string(buffer),
+			string(message),
+		)
+	}
+}
+
+type testError struct {
+	message string
+}
+
+func (e *testError) Error() string {
+	return e.message
+}

internal/client/integration_test.go

@@ -0,0 +1,308 @@
+/*
+ * ============================================================================
+ * Projekt.....: rs2322tcp
+ * Datei.......: integration_test.go
+ * Copyright (C) 2026 Dieter Lang
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ * Beschreibung:
+ * Integrationstest für die Client-/Server-Kommunikation einschließlich
+ * serieller Datenübertragung über virtuelle serielle Schnittstellen.
+ * ============================================================================
+ */
+
+package client_test
+
+import (
+	"fmt"
+	"io"
+	"net"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"git.lang-dieter.de/rs2322tcp/internal/client"
+	"git.lang-dieter.de/rs2322tcp/internal/config"
+	"git.lang-dieter.de/rs2322tcp/internal/server"
+)
+
+func startVirtualSerialPair(t *testing.T) (string, string, func()) {
+	t.Helper()
+
+	if _, err := exec.LookPath("socat"); err != nil {
+		t.Skip("socat not installed")
+	}
+
+	dir := t.TempDir()
+
+	portA := filepath.Join(dir, "ttyA")
+	portB := filepath.Join(dir, "ttyB")
+
+	cmd := exec.Command(
+		"socat",
+		"-d",
+		"-d",
+		fmt.Sprintf("pty,raw,echo=0,link=%s", portA),
+		fmt.Sprintf("pty,raw,echo=0,link=%s", portB),
+	)
+
+	if err := cmd.Start(); err != nil {
+		t.Fatalf("start socat: %v", err)
+	}
+
+	cleanup := func() {
+		if cmd.Process != nil {
+			_ = cmd.Process.Kill()
+			_ = cmd.Wait()
+		}
+	}
+
+	deadline := time.Now().Add(2 * time.Second)
+
+	for {
+		_, errA := os.Stat(portA)
+		_, errB := os.Stat(portB)
+
+		if errA == nil && errB == nil {
+			return portA, portB, cleanup
+		}
+
+		if time.Now().After(deadline) {
+			cleanup()
+			t.Fatal("timeout waiting for virtual serial ports")
+		}
+
+		time.Sleep(10 * time.Millisecond)
+	}
+}
+
+func readExactWithTimeout(
+	t *testing.T,
+	reader io.Reader,
+	buffer []byte,
+	timeout time.Duration,
+) {
+	t.Helper()
+
+	done := make(chan error, 1)
+
+	go func() {
+		_, err := io.ReadFull(reader, buffer)
+		done <- err
+	}()
+
+	select {
+	case err := <-done:
+		if err != nil {
+			t.Fatalf("read failed: %v", err)
+		}
+
+	case <-time.After(timeout):
+		t.Fatalf("read timeout after %s", timeout)
+	}
+}
+
+func TestClientServerSerialIntegration(t *testing.T) {
+	serialA, serialB, cleanup := startVirtualSerialPair(t)
+	defer cleanup()
+
+	////////////////////////////////////////////////////////////////////////////
+	// Server
+	////////////////////////////////////////////////////////////////////////////
+
+	controlProbe, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("find free control port: %v", err)
+	}
+
+	controlAddr := controlProbe.Addr().(*net.TCPAddr)
+	controlPort := controlAddr.Port
+
+	if err := controlProbe.Close(); err != nil {
+		t.Fatalf("close control probe: %v", err)
+	}
+
+	cfg := &config.ServerConfig{
+		Listen: config.ListenConfig{
+			Address: "127.0.0.1",
+			Port:    controlPort,
+		},
+		Devices: []config.DeviceConfig{
+			{
+				ID:         "radio",
+				Name:       "Funkgerät",
+				SerialPort: serialA,
+				BaudRate:   9600,
+				DataBits:   8,
+				Parity:     "none",
+				StopBits:   1,
+			},
+		},
+	}
+
+	srv, err := server.NewControlServer(cfg)
+	if err != nil {
+		t.Fatalf("NewControlServer() failed: %v", err)
+	}
+
+	////////////////////////////////////////////////////////////////////////////
+	// Control server
+	////////////////////////////////////////////////////////////////////////////
+
+	if err := srv.Listen(); err != nil {
+		t.Fatalf("server Listen() failed: %v", err)
+	}
+
+	serveDone := make(chan error, 1)
+
+	go func() {
+		serveDone <- srv.Serve()
+	}()
+
+	address := srv.Addr().String()
+
+	////////////////////////////////////////////////////////////////////////////
+	// Client
+	////////////////////////////////////////////////////////////////////////////
+
+	c, err := client.New(address)
+	if err != nil {
+		t.Fatalf("client.New() failed: %v", err)
+	}
+	defer c.Close()
+
+	devices, err := c.GetDevices()
+	if err != nil {
+		t.Fatalf("GetDevices() failed: %v", err)
+	}
+
+	if len(devices) != 1 {
+		t.Fatalf(
+			"len(devices) = %d, want 1",
+			len(devices),
+		)
+	}
+
+	device := devices[0]
+
+	if device.ID != "radio" {
+		t.Fatalf(
+			"device ID = %q, want %q",
+			device.ID,
+			"radio",
+		)
+	}
+
+	if device.DataPort == 0 {
+		t.Fatal("server returned data port 0")
+	}
+
+	////////////////////////////////////////////////////////////////////////////
+	// Open data connection
+	////////////////////////////////////////////////////////////////////////////
+
+	dataConn, err := c.OpenDataConnection(device)
+	if err != nil {
+		t.Fatalf("OpenDataConnection() failed: %v", err)
+	}
+	defer dataConn.Close()
+
+	////////////////////////////////////////////////////////////////////////////
+	// Open serial peer
+	////////////////////////////////////////////////////////////////////////////
+
+	serialPeer, err := os.OpenFile(
+		serialB,
+		os.O_RDWR,
+		0,
+	)
+	if err != nil {
+		t.Fatalf("open serial peer: %v", err)
+	}
+	defer serialPeer.Close()
+
+	////////////////////////////////////////////////////////////////////////////
+	// Client -> TCP -> Server -> Serial
+	////////////////////////////////////////////////////////////////////////////
+
+	clientMessage := []byte("hello from client")
+
+	if _, err := dataConn.Write(clientMessage); err != nil {
+		t.Fatalf("client data Write() failed: %v", err)
+	}
+
+	serialReceived := make([]byte, len(clientMessage))
+
+	readExactWithTimeout(
+		t,
+		serialPeer,
+		serialReceived,
+		2*time.Second,
+	)
+
+	if string(serialReceived) != string(clientMessage) {
+		t.Fatalf(
+			"serial received %q, want %q",
+			string(serialReceived),
+			string(clientMessage),
+		)
+	}
+
+	////////////////////////////////////////////////////////////////////////////
+	// Serial -> Server -> TCP -> Client
+	////////////////////////////////////////////////////////////////////////////
+
+	serialMessage := []byte("hello from serial")
+
+	if _, err := serialPeer.Write(serialMessage); err != nil {
+		t.Fatalf("serial Write() failed: %v", err)
+	}
+
+	clientReceived := make([]byte, len(serialMessage))
+
+	readExactWithTimeout(
+		t,
+		dataConn,
+		clientReceived,
+		2*time.Second,
+	)
+
+	if string(clientReceived) != string(serialMessage) {
+		t.Fatalf(
+			"client received %q, want %q",
+			string(clientReceived),
+			string(serialMessage),
+		)
+	}
+
+	////////////////////////////////////////////////////////////////////////////
+	// Cleanup
+	////////////////////////////////////////////////////////////////////////////
+
+	if err := dataConn.Close(); err != nil {
+		t.Fatalf("close data connection: %v", err)
+	}
+
+	if err := c.Close(); err != nil {
+		t.Fatalf("close client: %v", err)
+	}
+
+	// Give the server goroutines a moment to perform their cleanup.
+	time.Sleep(20 * time.Millisecond)
+
+	if err := srv.Close(); err != nil {
+		t.Fatalf("close server: %v", err)
+	}
+
+	select {
+	case err := <-serveDone:
+		if err != nil {
+			t.Fatalf("server Serve() failed: %v", err)
+		}
+	case <-time.After(2 * time.Second):
+		t.Fatal("timeout waiting for server Serve() to stop")
+	}
+}