Visual Basic 6.0

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.

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Visual Basic 6.0

Dim success As Long
success = 0

Dim socket As New ChilkatSocket

'  Connect as plain TCP (no TLS yet).
Dim bTls As Long
bTls = 0
Dim maxWaitMs As Long
maxWaitMs = 5000
success = socket.Connect("example.com",5000,bTls,maxWaitMs)
If (success = 0) Then
    Debug.Print socket.LastErrorText
    Exit Sub
End If

'  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.
success = socket.ConvertToSsl()
If (success = 0) Then
    Debug.Print socket.LastErrorText
    Exit Sub
End If

Debug.Print "Connection upgraded to TLS."