Tcl

Upgrade a Plain TCP Connection to TLS

Demonstrates Socket.ConvertToSsl, which upgrades an already-connected plain TCP socket to TLS by performing a client-side TLS handshake over the existing connection.

Background. This supports STARTTLS-style upgrades, where a protocol begins in plaintext and switches to TLS at a defined point. Perform the protocol-specific negotiation first, then call ConvertToSsl.

Chilkat Tcl Downloads

Download Chilkat for Tcl

Tcl


load ./chilkat.dll

set success 0

set socket [new_CkSocket]

#  Connect as plain TCP (no TLS yet).
set bTls 0
set maxWaitMs 5000
set success [CkSocket_Connect $socket "example.com" 5000 $bTls $maxWaitMs]
if {$success == 0} then {
    puts [CkSocket_lastErrorText $socket]
    delete_CkSocket $socket
    exit
}

#  At the point where the application protocol permits a STARTTLS-style upgrade, perform any required
#  negotiation, then upgrade the existing connection to TLS with a client-side handshake.
set success [CkSocket_ConvertToSsl $socket]
if {$success == 0} then {
    puts [CkSocket_lastErrorText $socket]
    delete_CkSocket $socket
    exit
}

puts "Connection upgraded to TLS."

delete_CkSocket $socket