Add RunTransactions() approach to application design

example4/example4.go

@@ -0,0 +1,83 @@
+// This file is part of https://github.com/racingmars/go3270/
+// Copyright 2025 by Matthew R. Wilson, licensed under the MIT license. See
+// LICENSE in the project root for license information.
+
+// This example demonstrates using the RunTransactions() approach to
+// structuring a go3270 application.
+
+package main
+
+import (
+	"fmt"
+	"net"
+	"sync"
+
+	"github.com/racingmars/go3270"
+)
+
+type global struct {
+	usercount int // number of connected users
+	countlock sync.Mutex
+}
+
+// session is the structure which holds global state for a user session of our
+// application. The various Transactions will be methods on this struct.
+type session struct {
+	db   DB
+	user User
+
+	// We can also share global state between users
+	g *global
+}
+
+func main() {
+	// "Connect" to our database (for this example, it's just a mock in-memory
+	// database).
+	dbconn := Connect()
+
+	gblstate := new(global)
+
+	ln, err := net.Listen("tcp", ":3270")
+	if err != nil {
+		panic(err)
+	}
+	fmt.Println("LISTENING ON PORT 3270 FOR CONNECTIONS")
+	fmt.Println("Press Ctrl-C to end server.")
+	for {
+		conn, err := ln.Accept()
+		if err != nil {
+			panic(err)
+		}
+		go handle(conn, dbconn, gblstate)
+	}
+}
+
+// handle is the handler for individual user connections.
+func handle(conn net.Conn, db DB, gblstate *global) {
+	defer conn.Close()
+
+	// Create the state for this client's connection
+	state := session{
+		db: db,
+		g:  gblstate,
+	}
+
+	// Add to the global user counter
+	gblstate.countlock.Lock()
+	gblstate.usercount++
+	gblstate.countlock.Unlock()
+
+	// When the session ends, reduce the user count
+	defer func() {
+		gblstate.countlock.Lock()
+		gblstate.usercount--
+		gblstate.countlock.Unlock()
+	}()
+
+	// Always begin new connection by negotiating the telnet options
+	go3270.NegotiateTelnet(conn)
+	err := go3270.RunTransactions(conn, state.login, nil)
+	if err != nil {
+		fmt.Println(err)
+	}
+}