Add RunTransactions() approach to application design

transactions.go

@@ -0,0 +1,44 @@
+// 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.
+
+package go3270
+
+import "net"
+
+// Tx is a function that serves as one transaction in a go3270 application.
+// The Tx function is called with the network connection to the client, and a
+// "data" value provided by the previous transaction. Tx functions return the
+// next transaction to run (or nil to indicate the RunTransactions() function
+// should terminate), the data to pass into the next transaction, and any
+// error. If the error is non-nil, the RunTransactions() function will
+// terminate and return the err. A non-nil error is _not_ passed between
+// transactions, it terminates transaction processing.
+type Tx func(conn net.Conn, data any) (next Tx, newdata any, err error)
+
+// RunTransactions begins running transaction functions, starting with the
+// initial transaction, until a transaction eventually returns nil for the
+// next transaction, or until a transaction function returns a non-nil error
+// value. data (which may be nil, if the initial transaction does not require
+// data) is passed in as the data to the initial transaction.
+func RunTransactions(conn net.Conn, initial Tx, data any) error {
+	var next Tx
+	var err error
+
+	next = initial
+
+	// We run transactions until there isn't a next transaction to run, or
+	// an error.
+	for {
+		next, data, err = next(conn, data)
+		if err != nil {
+			// Error means we bail out and return the error to the caller.
+			return err
+		}
+
+		if next == nil {
+			// nil next transaction means we're done.
+			return nil
+		}
+	}
+}