PowerBuilder

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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PowerBuilder

integer li_rc
integer li_Success
oleobject loo_Tunnel
integer li_SshPort
string ls_Password
integer li_ListenPort
integer li_WaitForThreadExit

li_Success = 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.

loo_Tunnel = create oleobject
li_rc = loo_Tunnel.ConnectToNewObject("Chilkat.SshTunnel")
if li_rc < 0 then
    destroy loo_Tunnel
    MessageBox("Error","Connecting to COM object failed")
    return
end if

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

//  Disable Nagle's algorithm to reduce latency for small, interactive packets.
loo_Tunnel.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.
loo_Tunnel.OutboundBindIpAddress = "192.168.1.50"
loo_Tunnel.OutboundBindPort = 0

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

li_SshPort = 22
li_Success = loo_Tunnel.Connect("ssh.example.com",li_SshPort)
if li_Success = 0 then
    Write-Debug loo_Tunnel.LastErrorText
    destroy loo_Tunnel
    return
end if

//  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.
ls_Password = "mySshPassword"

li_Success = loo_Tunnel.AuthenticatePw("mySshLogin",ls_Password)
if li_Success = 0 then
    Write-Debug loo_Tunnel.LastErrorText
    destroy loo_Tunnel
    return
end if

li_ListenPort = 1080
li_Success = loo_Tunnel.BeginAccepting(li_ListenPort)
if li_Success = 0 then
    Write-Debug loo_Tunnel.LastErrorText
    destroy loo_Tunnel
    return
end if

Write-Debug "Tunnel established with custom socket options."

li_WaitForThreadExit = 1
li_Success = loo_Tunnel.CloseTunnel(li_WaitForThreadExit)
if li_Success = 0 then
    Write-Debug loo_Tunnel.LastErrorText
    destroy loo_Tunnel
    return
end if



destroy loo_Tunnel