Visual FoxPro

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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LOCAL lnSuccess
LOCAL loTunnel
LOCAL lnSshPort
LOCAL lcPassword
LOCAL lnListenPort
LOCAL lnWaitForThreadExit

lnSuccess = 0

*  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.

loTunnel = CreateObject('Chilkat.SshTunnel')

*  Socket send/receive buffer sizes, in bytes.  Larger buffers can help throughput on
*  high-latency links.
loTunnel.SoRcvBuf = 4194304
loTunnel.SoSndBuf = 262144

*  Disable Nagle's algorithm to reduce latency for small, interactive packets.
loTunnel.TcpNoDelay = 1

*  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.
loTunnel.OutboundBindIpAddress = "192.168.1.50"
loTunnel.OutboundBindPort = 0

loTunnel.DestHostname = "db.internal.example.com"
loTunnel.DestPort = 5432

lnSshPort = 22
lnSuccess = loTunnel.Connect("ssh.example.com",lnSshPort)
IF (lnSuccess = 0) THEN
    ? loTunnel.LastErrorText
    RELEASE loTunnel
    CANCEL
ENDIF

*  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.
lcPassword = "mySshPassword"

lnSuccess = loTunnel.AuthenticatePw("mySshLogin",lcPassword)
IF (lnSuccess = 0) THEN
    ? loTunnel.LastErrorText
    RELEASE loTunnel
    CANCEL
ENDIF

lnListenPort = 1080
lnSuccess = loTunnel.BeginAccepting(lnListenPort)
IF (lnSuccess = 0) THEN
    ? loTunnel.LastErrorText
    RELEASE loTunnel
    CANCEL
ENDIF

? "Tunnel established with custom socket options."

lnWaitForThreadExit = 1
lnSuccess = loTunnel.CloseTunnel(lnWaitForThreadExit)
IF (lnSuccess = 0) THEN
    ? loTunnel.LastErrorText
    RELEASE loTunnel
    CANCEL
ENDIF

RELEASE loTunnel