Tcl

Open a direct-tcpip Channel (SSH Port Forwarding)

Demonstrates the Chilkat Ssh.OpenDirectTcpIpChannel method, which opens a direct-tcpip channel through the SSH server to a target host and port. The first argument is the target hostname and the second is the target port. It returns the channel number, or -1 on failure.

Background: This is SSH local port forwarding at the API level: the channel carries ordinary TCP traffic to a service that may be reachable only from the SSH server's network — a database, an internal web app, a message broker. The key detail is that the server resolves the target name, not your machine, so it must resolve and be reachable there. Supplying a numeric IPv4 address avoids remote DNS resolution entirely.

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Tcl


load ./chilkat.dll

set success 0

#  Demonstrates the Ssh.OpenDirectTcpIpChannel method, which opens a direct-tcpip channel
#  through the SSH server to a target host and port.  The 1st argument is the target hostname
#  and the 2nd is the target port.  It returns the channel number, or -1 on failure.

set ssh [new_CkSsh]

set sshPort 22
set success [CkSsh_Connect $ssh "ssh.example.com" $sshPort]
if {$success == 0} then {
    puts [CkSsh_lastErrorText $ssh]
    delete_CkSsh $ssh
    exit
}

#  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.
set password "mySshPassword"

set success [CkSsh_AuthenticatePw $ssh "mySshLogin" $password]
if {$success == 0} then {
    puts [CkSsh_lastErrorText $ssh]
    delete_CkSsh $ssh
    exit
}

#  The target name is resolved by the SSH server, not by this computer, so it must be
#  reachable from the server's network.
set targetHostname "db.internal.example.com"
set targetPort 5432
set channelNum [CkSsh_OpenDirectTcpIpChannel $ssh $targetHostname $targetPort]
if {$channelNum < 0} then {
    puts [CkSsh_lastErrorText $ssh]
    delete_CkSsh $ssh
    exit
}

puts "Opened direct-tcpip channel: $channelNum"

#  The channel now carries ordinary TCP data to the target, tunneled over SSH.

CkSsh_Disconnect $ssh

delete_CkSsh $ssh