Tcl

TCP Socket through SSH Tunnel (Port Forwarding)

See more Socket/SSL/TLS Examples

Demonstrates using Chilkat Socket to communicate to a TCP service through an SSH tunnel. This example will connect to an NIST time server and (using the old Time Protocol (RFC 868)), will read the current GMT time.

Note: This is not necessarily a recommended means for getting the current date/time. The most commonly used time protocol is the Network Time Protocol (RFC-1305). The intent of this example is to show how TCP communications can occur through an SSH tunnel.

Tcl

load ./chilkat.dll

set success 0

# This example requires the Chilkat API to have been previously unlocked.
# See Global Unlock Sample for sample code.

set tunnel [new_CkSocket]

set sshHostname "sftp.example.com"
set sshPort 22

# Connect to an SSH server and establish the SSH tunnel:
set success [CkSocket_SshOpenTunnel $tunnel $sshHostname $sshPort]
if {$success == 0} then {
    puts [CkSocket_lastErrorText $tunnel]
    delete_CkSocket $tunnel
    exit
}

# Authenticate with the SSH server via a login/password
# or with a public key.
# This example demonstrates SSH password authentication.
set success [CkSocket_SshAuthenticatePw $tunnel "mySshLogin" "mySshPassword"]
if {$success == 0} then {
    puts [CkSocket_lastErrorText $tunnel]
    delete_CkSocket $tunnel
    exit
}

# OK, the SSH tunnel is setup.  Now open a channel within the tunnel.
# Once the channel is obtained, the Socket API may
# be used exactly the same as usual, except all communications
# are sent through the channel in the SSH tunnel.
# Any number of channels may be created from the same SSH tunnel.
# Multiple channels may coexist at the same time.

# Connect to an NIST time server and read the current date/time
set maxWaitMs 4000
set useTls 0
set channel [new_CkSocket]

set success [CkSocket_SshNewChannel $tunnel "time-c.nist.gov" 37 $useTls $maxWaitMs $channel]
if {$success == 0} then {
    puts [CkSocket_lastErrorText $tunnel]
    delete_CkSocket $tunnel
    delete_CkSocket $channel
    exit
}

# The time server will send a big-endian 32-bit integer representing
# the number of seconds since since 00:00 (midnight) 1 January 1900 GMT.
# The ReceiveInt32 method will receive a 4-byte integer, but returns
# 1 or 0 to indicate success.  If successful, the integer
# is obtained via the ReceivedInt property.
set bigEndian 1
set success [CkSocket_ReceiveInt32 $channel $bigEndian]
if {$success == 0} then {
    puts [CkSocket_lastErrorText $channel]
    delete_CkSocket $tunnel
    delete_CkSocket $channel
    exit
}

set dt [new_CkDateTime]

CkDateTime_SetFromNtpTime $dt [CkSocket_get_ReceivedInt $channel]

# Show the current local date/time
set bLocalTime 1
puts "Current local date/time: [CkDateTime_getAsRfc822 $dt $bLocalTime]"

# Close the SSH channel.
set success [CkSocket_Close $channel $maxWaitMs]
if {$success != 1} then {
    puts [CkSocket_lastErrorText $channel]
    delete_CkSocket $tunnel
    delete_CkSocket $channel
    delete_CkDateTime $dt
    exit
}

# It is possible to create a new channel from the existing SSH tunnel for the next connection:
# Any number of channels may be created from the same SSH tunnel.
# Multiple channels may coexist at the same time.
set success [CkSocket_SshNewChannel $tunnel "time-a.nist.gov" 37 $useTls $maxWaitMs $channel]
if {$success == 0} then {
    puts [CkSocket_lastErrorText $tunnel]
    delete_CkSocket $tunnel
    delete_CkSocket $channel
    delete_CkDateTime $dt
    exit
}

# Review the LastErrorText to see that the connection was made via the SSH tunnel:
puts [CkSocket_lastErrorText $tunnel]

# Close the connection to time-a.nist.gov.  This is actually closing our channel
# within the SSH tunnel, but keeps the tunnel open for the next port-forwarded connection.
set success [CkSocket_Close $channel $maxWaitMs]
if {$success != 1} then {
    puts [CkSocket_lastErrorText $channel]
    delete_CkSocket $tunnel
    delete_CkSocket $channel
    delete_CkDateTime $dt
    exit
}

# Finally, close the SSH tunnel.
set success [CkSocket_SshCloseTunnel $tunnel]
if {$success == 0} then {
    puts [CkSocket_lastErrorText $tunnel]
    delete_CkSocket $tunnel
    delete_CkSocket $channel
    delete_CkDateTime $dt
    exit
}

puts "TCP SSH tunneling example completed."

delete_CkSocket $tunnel
delete_CkSocket $channel
delete_CkDateTime $dt