71 lines
2.1 KiB
Go
71 lines
2.1 KiB
Go
// This file is part of https://github.com/racingmars/go3270/
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// Copyright 2020 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 go3270
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import (
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"net"
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"time"
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)
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const (
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binary = 0
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send = 1
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se = 240 // f0
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sb = 250 // fa
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will = 251 // fb
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wont = 252 // fc
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do = 253 // fd
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dont = 254 // fe
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iac = 255 // ff
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terminalType = 24 // 18
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eor = 25 // 19
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)
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// NegotiateTelnet will naively (e.g. not checking client responses) negotiate
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// the options necessary for tn3270 on a new telnet connection, conn.
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func NegotiateTelnet(conn net.Conn) error {
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conn.Write([]byte{iac, do, terminalType})
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conn.Write([]byte{iac, sb, terminalType, send, iac, se})
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conn.Write([]byte{iac, do, eor})
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conn.Write([]byte{iac, do, binary})
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conn.Write([]byte{iac, will, eor, iac, will, binary})
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flushConnection(conn, time.Second*5)
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return nil
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}
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// UnNegotiateTelnet will naively (e.g. not checking client responses) attempt
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// to restore the telnet options state to what it was before NegotiateTelnet()
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// was called.
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func UnNegotiateTelnet(conn net.Conn, timeout time.Duration) error {
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conn.Write([]byte{iac, wont, eor, iac, wont, binary})
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conn.Write([]byte{iac, dont, binary})
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conn.Write([]byte{iac, dont, eor})
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conn.Write([]byte{iac, dont, terminalType})
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flushConnection(conn, timeout)
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return nil
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}
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// flushConnection discards all bytes that it can read from conn, allowing up
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// to the duration timeout for the first byte to be read.
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func flushConnection(conn net.Conn, timeout time.Duration) error {
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defer conn.SetReadDeadline(time.Time{})
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buffer := make([]byte, 1024)
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for {
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conn.SetReadDeadline(time.Now().Add(timeout))
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n, err := conn.Read(buffer)
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if neterr, ok := err.(net.Error); ok && neterr.Timeout() {
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debugf("nothing to flush\n")
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return nil
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}
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if err != nil {
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debugf("error while flushing: %v\n", err)
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return err
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}
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debugf("%d bytes read while flushing connection\n", n)
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// for follow-up reads, reduce the timeout
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timeout = time.Second / 2
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}
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}
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