Add RunTransactions() approach to application design
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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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// This example demonstrates using the RunTransactions() approach to
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// structuring a go3270 application.
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// This file contains the login and user registration transactions.
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package main
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import (
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"net"
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"github.com/racingmars/go3270"
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)
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const loginUsername = "username"
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const loginPassword = "password"
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const loginPasswordConf = "password confirmation"
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const loginName = "name"
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const loginErr = "errormsg"
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var loginScreen = go3270.Screen{
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{Row: 0, Col: 37, Intense: true, Content: "Logon"},
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{Row: 2, Col: 0,
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Content: "Welcome to the go3270 example application. Please log on."},
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// Username
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{Row: 4, Col: 0, Content: "Username . . .", Color: go3270.Green},
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{Row: 4, Col: 15, Name: loginUsername, Write: true,
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Highlighting: go3270.Underscore, Color: go3270.Turquoise},
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{Row: 4, Col: 24, Autoskip: true}, // field "stop" character
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// Password
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{Row: 5, Col: 0, Content: "Password . . .", Color: go3270.Green},
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{Row: 5, Col: 15, Name: loginPassword, Write: true, Hidden: true},
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{Row: 5, Col: 79}, // field "stop" character
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// Registration instructions
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{Row: 7, Col: 0, Content: "If you don't yet have an account, press"},
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{Row: 7, Col: 40, Content: "PF5", Color: go3270.White, Intense: true},
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{Row: 7, Col: 44, Content: "to register a new account."},
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// Error message
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{Row: 21, Col: 0, Name: loginErr, Color: go3270.Red, Intense: true},
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// Key legend
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{Row: 23, Col: 1, Content: "F1=Help"},
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{Row: 23, Col: 14, Content: "F3=Exit"},
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{Row: 23, Col: 27, Content: "F5=Register"},
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}
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var loginScreenRules = go3270.Rules{
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loginUsername: {Validator: go3270.NonBlank},
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loginPassword: {Validator: go3270.NonBlank, Reset: true},
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}
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// login transaction accepts a string value in data if the login screen
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// should be initialized with an error message.
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func (sess *session) login(conn net.Conn, data any) (go3270.Tx, any, error) {
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fieldValues := make(map[string]string)
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if data != nil {
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if errmsg, ok := data.(string); ok {
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fieldValues[loginErr] = errmsg
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}
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}
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resp, err := go3270.HandleScreen(
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loginScreen, // the screen to display
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loginScreenRules, // the rules to enforce
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fieldValues, // pre-populated values in fields
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[]go3270.AID{go3270.AIDEnter}, // 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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go3270.AIDPF5,
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go3270.AIDClear},
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loginErr, // name of field to put error messages in
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4, 16, // cursor coordinates
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conn)
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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.AIDClear:
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// re-run the transaction with empty values
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return sess.login, nil, nil
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case go3270.AIDPF1:
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// Display help transaction, then return to this transaction
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return help(sess.login), nil, nil
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case go3270.AIDPF3:
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// User wants to quit; return no next transaction
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return nil, nil, nil
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case go3270.AIDPF5:
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// Send user to registration transaction
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return sess.newuser, nil, nil
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}
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// If we didn't get one of the other allowed keys, try to log the user in.
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username := resp.Values[loginUsername]
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password := resp.Values[loginPassword]
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user, err := sess.db.GetUser(username)
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// NOTE: this is just an example application. Obviously in a real
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// application, password hashing would be in place.
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if err != nil || user.Password != password {
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// If we couldn't get the username from the DB, or if the password
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// doesn't match, re-run the login transaction with an error
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// message displayed.
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return sess.login, "Username or password not valid.", nil
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}
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// Login was successful. Update the session state to the logged-in user.
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sess.user = user
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return sess.mainmenu, nil, nil
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}
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var newuserScreen = go3270.Screen{
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{Row: 0, Col: 30, Intense: true, Content: "New User Registration"},
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{Row: 2, Col: 0,
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Content: "Please provide your user registration details."},
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// Username
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{Row: 4, Col: 0, Content: "Username . . .", Color: go3270.Green},
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{Row: 4, Col: 15, Name: loginUsername, Write: true,
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Highlighting: go3270.Underscore, Color: go3270.Turquoise},
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{Row: 4, Col: 24, Autoskip: true}, // field "stop" character
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// Password
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{Row: 5, Col: 0, Content: "Password . . .", Color: go3270.Green},
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{Row: 5, Col: 15, Name: loginPassword, Write: true, Hidden: true},
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{Row: 5, Col: 79, Autoskip: true}, // field "stop" character
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// Password
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{Row: 6, Col: 0, Content: "Confirm Pass .", Color: go3270.Green},
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{Row: 6, Col: 15, Name: loginPasswordConf, Write: true, Hidden: true},
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{Row: 6, Col: 79, Autoskip: true}, // field "stop" character
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// Name
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{Row: 7, Col: 0, Content: "Name . . . . .", Color: go3270.Green},
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{Row: 7, Col: 15, Name: loginName, Write: true,
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Highlighting: go3270.Underscore, Color: go3270.Turquoise},
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{Row: 7, Col: 46, Autoskip: true}, // field "stop" character
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// Error message
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{Row: 21, Col: 0, Name: loginErr, Color: go3270.Red, Intense: true},
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// Key legend
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{Row: 23, Col: 1, Content: "F1=Help"},
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{Row: 23, Col: 14, Content: "F3=Exit"},
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}
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var newuserScreenRules = go3270.Rules{
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loginUsername: {Validator: go3270.NonBlank},
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loginPassword: {Validator: go3270.NonBlank, Reset: true},
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loginPasswordConf: {Validator: go3270.NonBlank, Reset: true},
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}
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// newuserData is the data that can be passed into the newuser transaction
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type newuserData struct {
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username string
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name string
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errmsg string
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}
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func (sess *session) newuser(conn net.Conn, data any) (go3270.Tx, any, error) {
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fieldValues := make(map[string]string)
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if data != nil {
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if newdata, ok := data.(newuserData); ok {
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fieldValues[loginUsername] = newdata.username
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fieldValues[loginName] = newdata.name
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fieldValues[loginErr] = newdata.errmsg
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}
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}
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resp, err := go3270.HandleScreen(
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newuserScreen, // the screen to display
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newuserScreenRules, // the rules to enforce
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fieldValues, // pre-populated values in fields
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[]go3270.AID{go3270.AIDEnter}, // 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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go3270.AIDClear,
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},
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loginErr, // name of field to put error messages in
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4, 16, // cursor coordinates
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conn)
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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.AIDClear:
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// Re-run transaction with empty values
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return sess.newuser, nil, nil
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case go3270.AIDPF1:
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// Display help screen, returning to this transaction after
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return help(sess.newuser), nil, nil
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case go3270.AIDPF3:
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// User wants to cancel registration, go back to login screen.
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return sess.login, nil, nil
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}
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// Otherwise, we'll try creating the user.
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username := resp.Values[loginUsername]
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password := resp.Values[loginPassword]
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passwordConf := resp.Values[loginPasswordConf]
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name := resp.Values[loginName]
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if password != passwordConf {
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// Re-run the newuser transaction with an error message
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return sess.newuser, newuserData{
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username: username,
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name: name,
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errmsg: "Passwords do not match.",
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}, nil
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}
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user, err := sess.db.CreateUser(User{
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Username: username,
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Password: password,
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Name: name,
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})
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if err == ErrUserExists {
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// Re-run the newuser transaction with an error message
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return sess.newuser, newuserData{
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username: username,
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name: name,
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errmsg: "Username already exists; please choose a new one.",
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}, nil
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}
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if err != nil {
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return sess.newuser, newuserData{
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username: username,
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name: name,
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errmsg: "Unknown error creating new user.",
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}, nil
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}
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// Success! We'll stick the new user in the session state like login does
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// and go to the main menu.
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sess.user = user
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return sess.mainmenu, nil, nil
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}
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