Swift

SSH Tunnel TCP Socket Options

Demonstrates tuning the underlying TCP socket with the SoRcvBuf, SoSndBuf, TcpNoDelay, OutboundBindIpAddress, and OutboundBindPort properties. These normally should be left at their defaults.

Background: These are low-level knobs for specific situations. Larger send/receive buffers can improve throughput on high-bandwidth, high-latency ("long fat") links; TcpNoDelay disables Nagle's algorithm to cut latency for small interactive packets at the cost of efficiency; and binding the outbound socket to a specific local address or port is occasionally required by firewall rules or multi-homed hosts. Change them only with a concrete reason, since the defaults are tuned for the common case.

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Swift


func chilkatTest() {
    var success: Bool = false

    //  Demonstrates tuning the underlying TCP socket with the SshTunnel properties SoRcvBuf, SoSndBuf,
    //  TcpNoDelay, OutboundBindIpAddress, and OutboundBindPort.
    //  
    //  These normally should be left at their defaults; adjust them only for specific performance or
    //  networking requirements.

    let tunnel = CkoSshTunnel()!

    //  Socket send/receive buffer sizes, in bytes.  Larger buffers can help throughput on
    //  high-latency links.
    tunnel.soRcvBuf = 4194304
    tunnel.soSndBuf = 262144

    //  Disable Nagle's algorithm to reduce latency for small, interactive packets.
    tunnel.tcpNoDelay = true

    //  Bind the outbound socket to a specific local address/port before connecting.  0 (the default)
    //  lets the OS choose the local port; an empty address lets the OS choose the interface.
    tunnel.outboundBindIpAddress = "192.168.1.50"
    tunnel.outboundBindPort = 0

    tunnel.destHostname = "db.internal.example.com"
    tunnel.destPort = 5432

    var sshPort: Int = 22
    success = tunnel.connect(hostname: "ssh.example.com", port: sshPort)
    if success == false {
        print("\(tunnel.lastErrorText!)")
        return
    }

    //  Normally you would not hard-code the password in source.  You should instead obtain it
    //  from an interactive prompt, environment variable, or a secrets vault.
    var password: String? = "mySshPassword"

    success = tunnel.authenticatePw(login: "mySshLogin", password: password)
    if success == false {
        print("\(tunnel.lastErrorText!)")
        return
    }

    var listenPort: Int = 1080
    success = tunnel.beginAccepting(listenPort: listenPort)
    if success == false {
        print("\(tunnel.lastErrorText!)")
        return
    }

    print("Tunnel established with custom socket options.")

    var waitForThreadExit: Bool = true
    success = tunnel.closeTunnel(waitForThreads: waitForThreadExit)
    if success == false {
        print("\(tunnel.lastErrorText!)")
        return
    }


}