first init

examples/tls_client.go

@@ -0,0 +1,92 @@
+package main
+
+import (
+	"crypto/tls"
+	"crypto/x509"
+	"fmt"
+	"os"
+
+	"github.com/simonvetter/modbus"
+)
+
+/*
+ * Modbus client with TLS example.
+ *
+ * This file is intended to be a demo of the modbus client in TCP+TLS
+ * mode. It shows how to load certificates from files and how to
+ * configure the client to use them.
+ */
+
+func main() {
+	var client         *modbus.ModbusClient
+	var err            error
+	var clientKeyPair  tls.Certificate
+	var serverCertPool *x509.CertPool
+	var regs           []uint16
+
+	// load the client certificate and its associated private key, which
+	// are used to authenticate the client to the server
+	clientKeyPair, err = tls.LoadX509KeyPair(
+		"certs/client.cert.pem", "certs/client.key.pem")
+	if err != nil {
+		fmt.Printf("failed to load client key pair: %v\n", err)
+		os.Exit(1)
+	}
+
+	// load either the server certificate or the certificate of the CA
+	// (Certificate Authority) which signed the server certificate
+	serverCertPool, err = modbus.LoadCertPool("certs/server.cert.pem")
+	if err != nil {
+		fmt.Printf("failed to load server certificate/CA: %v\n", err)
+		os.Exit(1)
+	}
+
+	// create a client targetting host secure-plc on port 802 using
+	// modbus TCP over TLS (MBAPS)
+	client, err = modbus.NewClient(&modbus.ClientConfiguration{
+		// tcp+tls is the moniker for MBAPS (modbus/tcp encapsulated in
+		// TLS),
+		// 802/tcp is the IANA-registered port for MBAPS.
+		URL:           "tcp+tls://secure-plc:802",
+		// set the client-side cert and key
+		TLSClientCert: &clientKeyPair,
+		// set the server/CA certificate
+		TLSRootCAs:    serverCertPool,
+	})
+	if err != nil {
+		fmt.Printf("failed to create modbus client: %v\n", err)
+		os.Exit(1)
+	}
+
+	// now that the client is created and configured, attempt to connect
+	err = client.Open()
+	if err != nil {
+		fmt.Printf("failed to connect: %v\n", err)
+		os.Exit(2)
+	}
+
+	// read two 16-bit holding registers at address 0x4000
+	regs, err = client.ReadRegisters(0x4000, 2, modbus.HOLDING_REGISTER)
+	if err != nil {
+		fmt.Printf("failed to read registers 0x4000 and 0x4001: %v\n", err)
+	} else {
+		fmt.Printf("register 0x4000: 0x%04x\n", regs[0])
+		fmt.Printf("register 0x4001: 0x%04x\n", regs[1])
+	}
+
+	// set register 0x4002 to 500
+	err = client.WriteRegister(0x4002, 500)
+	if err != nil {
+		fmt.Printf("failed to write to register 0x4002: %v\n", err)
+	} else {
+		fmt.Printf("set register 0x4002 to 500\n")
+	}
+
+	// close the connection
+	err = client.Close()
+	if err != nil {
+		fmt.Printf("failed to close connection: %v\n", err)
+	}
+
+	os.Exit(0)
+}