From 176201866273bf7f8cf9b1f5c2b172a53a6b258a Mon Sep 17 00:00:00 2001
From: FM-FE <goo.fm.fe@gmail.com>
Date: Fri, 27 Jun 2025 10:14:04 +0800
Subject: [PATCH] feat: add support for slave start TCP connect as client

---
 README.md    | 12 ++++++++++++
 tcpclient.go |  7 +++++++
 2 files changed, 19 insertions(+)

diff --git a/README.md b/README.md
index e952636..a555070 100644
--- a/README.md
+++ b/README.md
@@ -50,6 +50,18 @@ handler.Logger = log.New(os.Stdout, "test: ", log.LstdFlags)
 err := handler.Connect()
 defer handler.Close()
 
+client := modbus.NewClient(handler)
+results, err := client.ReadDiscreteInputs(15, 2)
+results, err = client.WriteMultipleRegisters(1, 2, []byte{0, 3, 0, 4})
+results, err = client.WriteMultipleCoils(5, 10, []byte{4, 3})
+
+// Modbus TCP slave start TCP connect as client
+listener, err := net.Listen("tcp", "MasterIP:Port")
+conn, err := listener.Accept()
+handler := modbus.NewTCPClientHandler("")
+handler.UseConnect(conn) // listen conn from slave
+defer handler.Close()
+
 client := modbus.NewClient(handler)
 results, err := client.ReadDiscreteInputs(15, 2)
 results, err = client.WriteMultipleRegisters(1, 2, []byte{0, 3, 0, 4})
diff --git a/tcpclient.go b/tcpclient.go
index 4e53c73..447d375 100644
--- a/tcpclient.go
+++ b/tcpclient.go
@@ -217,6 +217,13 @@ func (mb *tcpTransporter) connect() error {
 	return nil
 }
 
+func (mb *tcpTransporter) UseConnect(conn net.Conn) error {
+	if mb.conn == nil {
+		mb.conn = conn
+	}
+	return nil
+}
+
 func (mb *tcpTransporter) startCloseTimer() {
 	if mb.IdleTimeout <= 0 {
 		return