Alternate screen size support.

This is a relatively big new feature, which introduces small breaking changes
to the API:

 * NegotiateTelnet() now returns (DevInfo, error) instead of just error.  The
   function signature for the Tx type now has one additional DevInfo parameter.
 * RunTransactions() requires one additional parameter, the DevInfo (which is
   allowed to be nil).

Otherwise, existing behavior continues to work as-is and everything still
defaults to operating on the default 24x80 terminal size.

See example5 for a larger-terminal-aware application.

Pending some time to make sure no new bugs cropped up in this release and that
the alternate screen size support works in the wild, I anticipate this will
become the v1.0.0 release of go3270.

example4/example4.go

@@ -75,8 +75,13 @@ func handle(conn net.Conn, db DB, gblstate *global) {
 	}()
 
 	// Always begin new connection by negotiating the telnet options
-	go3270.NegotiateTelnet(conn)
-	err := go3270.RunTransactions(conn, state.login, nil)
+	devinfo, err := go3270.NegotiateTelnet(conn)
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+
+	err = go3270.RunTransactions(conn, devinfo, state.login, nil)
 	if err != nil {
 		fmt.Println(err)
 	}

example4/help.go

@@ -48,7 +48,8 @@ var helpScreen = go3270.Screen{
 // generator function for it is a stand-alone function and not a method on the
 // session.
 func help(returnTransaction go3270.Tx) go3270.Tx {
-	return func(conn net.Conn, data any) (go3270.Tx, any, error) {
+	return func(conn net.Conn, _ go3270.DevInfo, data any) (
+		go3270.Tx, any, error) {
 		_, err := go3270.HandleScreen(
 			helpScreen,                  // the screen to display
 			nil,                         // (no) rules to enforce

example4/login.go

@@ -58,7 +58,8 @@ var loginScreenRules = go3270.Rules{
 
 // login transaction accepts a string value in data if the login screen
 // should be initialized with an error message.
-func (sess *session) login(conn net.Conn, data any) (go3270.Tx, any, error) {
+func (sess *session) login(conn net.Conn, _ go3270.DevInfo,
+	data any) (go3270.Tx, any, error) {
 
 	fieldValues := make(map[string]string)
 
@@ -169,7 +170,8 @@ type newuserData struct {
 	errmsg   string
 }
 
-func (sess *session) newuser(conn net.Conn, data any) (go3270.Tx, any, error) {
+func (sess *session) newuser(conn net.Conn, _ go3270.DevInfo, data any) (
+	go3270.Tx, any, error) {
 
 	fieldValues := make(map[string]string)
 

example4/mainmenu.go

@@ -79,7 +79,8 @@ type mainmenuData struct {
 
 // mainmenu transaction accepts a mainmenuData struct as the data if the
 // option field or error message should be populated.
-func (sess *session) mainmenu(conn net.Conn, data any) (go3270.Tx, any, error) {
+func (sess *session) mainmenu(conn net.Conn, _ go3270.DevInfo, data any) (
+	go3270.Tx, any, error) {
 
 	fieldValues := make(map[string]string)
 
@@ -182,8 +183,8 @@ var exampleScreen = go3270.Screen{
 // exampleFeature is a transaction that will act as a placeholder for real
 // application functionality. It accepts a string in the data which will
 // be displayed on the panel.
-func (sess *session) exampleFeature(conn net.Conn, data any) (go3270.Tx,
-	any, error) {
+func (sess *session) exampleFeature(conn net.Conn, _ go3270.DevInfo,
+	data any) (go3270.Tx, any, error) {
 
 	fieldValues := make(map[string]string)