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.
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Matthew R. Wilson committed
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// This file is part of https://github.com/racingmars/go3270/
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// Copyright 2025 by Matthew R. Wilson, licensed under the MIT license. See
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// LICENSE in the project root for license information.
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package main
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import (
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"fmt"
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"net"
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"strconv"
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"github.com/racingmars/go3270"
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)
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var biglayout = go3270.Screen{
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// Column will be calculated at runtime for the following field:
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{Row: 0, Intense: true, Content: "3270 Screen Size Example"},
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{Row: 2, Col: 0,
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Content: "This screen is using the full size that your terminal supports."},
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{Row: 4, Col: 0, Content: "Terminal Type . . ."},
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{Row: 4, Col: 21, Name: "termtype", Intense: true},
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{Row: 5, Col: 0, Content: "Rows . . . . . . . ."},
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{Row: 5, Col: 21, Name: "rows", Intense: true},
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{Row: 6, Col: 0, Content: "Columns . . . . . ."},
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{Row: 6, Col: 21, Name: "cols", Intense: true},
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{Row: 8, Col: 0, Content: "To visit a default sized screen, press"},
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{Row: 8, Col: 39, Content: "PF1", Color: go3270.Yellow, Intense: true},
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{Row: 9, Col: 0, Content: "To exit and disconnect, press"},
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{Row: 9, Col: 30, Content: "PF3", Color: go3270.Yellow, Intense: true},
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// a blank field for error messages
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{Row: 11, Col: 0, Intense: true, Color: go3270.Red, Name: "errormsg"},
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}
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func bigscreen(conn net.Conn, devinfo go3270.DevInfo, data any) (
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go3270.Tx, any, error) {
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rows, cols := devinfo.AltDimensions()
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termtype := devinfo.TerminalType()
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// Make a local copy of the screen definition that we can append lines to.
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screen := make(go3270.Screen, len(biglayout))
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copy(screen, biglayout)
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// Center the title on any screen width
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screen[0].Col = (cols / 2) - (len(biglayout[0].Content) / 2)
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// We'll start writing "data lines" at row 13 up to the penultimate row on
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// the terminal
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for i := 13; i < rows-1; i++ {
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newfield := go3270.Field{Row: i, Col: 0,
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Content: fmt.Sprintf("This is data row %d.", i-12)}
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if i == rows-2 {
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newfield.Content += " (The last.)"
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}
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screen = append(screen, newfield)
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// And demonstrate that we can position to the full width, too.
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newfield = go3270.Field{Row: i, Col: cols - 5, Content: "<**>"}
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screen = append(screen, newfield)
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}
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// And an input field on the last row, to make sure field buffer address
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// decoding works on larger screens.
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newfield := go3270.Field{Row: rows - 1, Col: 0,
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Content: "Enter data here:", Color: go3270.Pink, Intense: true}
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screen = append(screen, newfield)
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newfield = go3270.Field{Row: rows - 1, Col: 17, Name: "inputdata",
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Write: true}
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screen = append(screen, newfield)
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newfield = go3270.Field{Row: rows - 1, Col: cols - 1} // "stop" field
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screen = append(screen, newfield)
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fieldValues := map[string]string{
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"termtype": termtype,
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"rows": strconv.Itoa(rows),
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"cols": strconv.Itoa(cols),
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}
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if data != nil {
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fieldValues["errormsg"] = fmt.Sprintf("You said: %s", data.(string))
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}
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resp, err := go3270.HandleScreenAlt(
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screen, // the screen to display
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nil, // (no) rules to enforce
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fieldValues, // pre-populated values in fields
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[]go3270.AID{ // keys we accept -- validating
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go3270.AIDEnter,
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},
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[]go3270.AID{ // keys we accept -- non-validating
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go3270.AIDPF1,
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go3270.AIDPF3,
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},
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"errormsg", // name of field to put error messages in
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rows-1, 18, // cursor coordinates
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conn, // network connection
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devinfo, // device info for alternate screen size support
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)
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if err != nil {
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return nil, nil, err
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}
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switch resp.AID {
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case go3270.AIDEnter:
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// Re-run current transaction, echoing back input
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return bigscreen, resp.Values["inputdata"], err
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case go3270.AIDPF1:
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// Go to default screen size transaction
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return normalscreen, nil, nil
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case go3270.AIDPF3:
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// Exit
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return nil, nil, nil
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default:
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// re-run current transaction
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return bigscreen, nil, nil
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}
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}
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@@ -0,0 +1,48 @@
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// This file is part of https://github.com/racingmars/go3270/
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// Copyright 2025 by Matthew R. Wilson, licensed under the MIT license. See
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// LICENSE in the project root for license information.
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// Example 5 demonstrates support for larger-than-default alternate screen
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// sizes in terminals that are larger than 24x80.
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package main
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import (
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"fmt"
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"net"
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"github.com/racingmars/go3270"
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)
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func main() {
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ln, err := net.Listen("tcp", ":3270")
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if err != nil {
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panic(err)
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}
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fmt.Println("LISTENING ON PORT 3270 FOR CONNECTIONS")
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fmt.Println("Press Ctrl-C to end server.")
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for {
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conn, err := ln.Accept()
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if err != nil {
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panic(err)
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}
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go handle(conn)
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}
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}
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// handle is the handler for individual user connections.
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func handle(conn net.Conn) {
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defer conn.Close()
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// Always begin new connection by negotiating the telnet options
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devinfo, err := go3270.NegotiateTelnet(conn)
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if err != nil {
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fmt.Println(err)
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return
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}
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err = go3270.RunTransactions(conn, devinfo, bigscreen, nil)
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if err != nil {
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fmt.Println(err)
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}
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}
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@@ -0,0 +1,103 @@
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// This file is part of https://github.com/racingmars/go3270/
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// Copyright 2025 by Matthew R. Wilson, licensed under the MIT license. See
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// LICENSE in the project root for license information.
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package main
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import (
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"fmt"
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"net"
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"strconv"
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"github.com/racingmars/go3270"
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)
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var normallayout = go3270.Screen{
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{Row: 0, Col: 28, Intense: true, Content: "3270 Screen Size Example"},
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{Row: 2, Col: 0,
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Content: "This screen is using the default size that all terminals support, 24x80."},
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{Row: 3, Col: 0,
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Content: "But I know the following information about your particular terminal:"},
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{Row: 4, Col: 0, Content: "Terminal Type . . ."},
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{Row: 4, Col: 21, Name: "termtype", Intense: true},
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{Row: 5, Col: 0, Content: "Rows . . . . . . . ."},
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{Row: 5, Col: 21, Name: "rows", Intense: true},
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{Row: 5, Col: 28, Content: "(but currently using 24)"},
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{Row: 6, Col: 0, Content: "Columns . . . . . ."},
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{Row: 6, Col: 21, Name: "cols", Intense: true},
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{Row: 6, Col: 28, Content: "(but currently using 80)"},
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{Row: 8, Col: 0, Content: "To visit a large sized screen, press"},
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{Row: 8, Col: 37, Content: "PF1", Color: go3270.Yellow, Intense: true},
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{Row: 9, Col: 0, Content: "To exit and disconnect, press"},
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{Row: 9, Col: 30, Content: "PF3", Color: go3270.Yellow, Intense: true},
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// a blank field for error messages
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{Row: 11, Col: 0, Intense: true, Color: go3270.Red, Name: "errormsg"},
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}
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func normalscreen(conn net.Conn, devinfo go3270.DevInfo, data any) (
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go3270.Tx, any, error) {
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rows, cols := devinfo.AltDimensions()
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termtype := devinfo.TerminalType()
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// Make a local copy of the screen definition that we can append lines to.
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screen := make(go3270.Screen, len(normallayout))
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copy(screen, normallayout)
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// We'll start writing "data lines" at row 13 up to 24
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for i := 13; i < 24; i++ {
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newfield := go3270.Field{Row: i, Col: 0,
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Content: fmt.Sprintf("This is data row %d.", i-12)}
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if i == 23 {
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newfield.Content += " (The last.)"
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}
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screen = append(screen, newfield)
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newfield = go3270.Field{Row: i, Col: 80 - 5, Content: "<**>"}
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screen = append(screen, newfield)
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}
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fieldValues := map[string]string{
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"termtype": termtype,
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"rows": strconv.Itoa(rows),
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"cols": strconv.Itoa(cols),
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}
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// We can call the old HandleScreen(), or we could have used the new
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// HandleScreenAlt() and provided a nil DevInfo.
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resp, err := go3270.HandleScreen(
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screen, // the screen to display
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nil, // (no) rules to enforce
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fieldValues, // pre-populated values in fields
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nil, // keys we accept -- validating
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[]go3270.AID{ // keys we accept -- non-validating
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go3270.AIDPF1,
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go3270.AIDPF3,
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},
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"errormsg", // name of field to put error messages in
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1, 1, // cursor coordinates
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conn, // network connection
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)
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if err != nil {
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return nil, nil, err
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}
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switch resp.AID {
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case go3270.AIDPF1:
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// Go to big screen size transaction
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return bigscreen, nil, nil
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case go3270.AIDPF3:
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// Exit
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return nil, nil, nil
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default:
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// re-run current transaction
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return normalscreen, nil, nil
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}
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}
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