Xojo Plugin

SSH Tunnel (Port Forwarding via direct-tcpip Channel)

Demonstrates creating an SSH tunnel to a remote host:port using a direct-tcpip channel. Data written to the channel is forwarded by the SSH server to the target, and data read back is whatever the target sent. This example tunnels a simple HTTP GET request to a web server.

Background: This is SSH local port forwarding at the API level, and the target need not be a web server — it can be a database, a message broker, or any TCP service. The key detail is that the SSH server resolves and connects to the target, not your machine, so the destination only has to be reachable from the server's network. That is what makes tunneling useful for reaching services behind a firewall. Note the receive pattern here: read until the double CRLF that ends an HTTP header, extract exactly that with GetReceivedTextS, then poll briefly for the body, which may already have arrived.

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Dim success As Boolean
success = False

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

//  Demonstrates creating an SSH tunnel to a remote host:port using a direct-tcpip channel.
//  Data written to the channel is forwarded by the SSH server to the target host:port, and data
//  read from the channel is whatever the target sent back.

Dim ssh As New Chilkat.Ssh

Dim hostname As String
hostname = "ssh.example.com"
Dim port As Int32
port = 22
success = ssh.Connect(hostname,port)
If (success = False) Then
    System.DebugLog(ssh.LastErrorText)
    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.
Dim password As String
password = "mySshPassword"

success = ssh.AuthenticatePw("mySshLogin",password)
If (success = False) Then
    System.DebugLog(ssh.LastErrorText)
    Return
End If

//  Ask the SSH server to connect onward to this host:port.  The target is resolved by the SSH
//  server, not by this computer, so it must be reachable from the server's network.  The target
//  need not be a web server -- it can be any TCP service.
Dim targetHost As String
targetHost = "www.chilkatsoft.com"
Dim targetPort As Int32
targetPort = 80
Dim channelNum As Int32
channelNum = ssh.OpenDirectTcpIpChannel(targetHost,targetPort)
If (channelNum < 0) Then
    System.DebugLog(ssh.LastErrorText)
    Return
End If

//  Send a simple HTTP GET request through the tunnel.
Dim httpReq As String
httpReq = "GET /xyz123.html HTTP/1.1" + EndOfLine.Windows + "Host: www.chilkatsoft.com" + EndOfLine.Windows + EndOfLine.Windows
success = ssh.ChannelSendString(channelNum,httpReq,"utf-8")
If (success = False) Then
    System.DebugLog(ssh.LastErrorText)
    Return
End If

//  IMPORTANT: Set a read timeout before receiving until a match.  ReadTimeoutMs defaults to 0,
//  which means no limit -- without it, this call waits forever if the received data never
//  contains a match.
ssh.ReadTimeoutMs = 15000

//  An HTTP response header ends with a blank line, so receive until a double CRLF is seen.
//  The method may read beyond the match, but it stops waiting as soon as the match appears.
Dim caseSensitive As Boolean
caseSensitive = False
Dim matchStr As String
matchStr = EndOfLine.Windows + EndOfLine.Windows
success = ssh.ChannelReceiveUntilMatch(channelNum,matchStr,"utf-8",caseSensitive)
If (success = False) Then
    System.DebugLog(ssh.LastErrorText)
    Return
End If

//  GetReceivedTextS removes everything through and including the match, which is exactly the
//  response header.
Dim responseHeader As String
responseHeader = ssh.GetReceivedTextS(channelNum,matchStr,"utf-8")
If (ssh.LastMethodSuccess = False) Then
    System.DebugLog(ssh.LastErrorText)
    Return
End If

System.DebugLog("---- HTTP Response Header ----")
System.DebugLog(responseHeader)

//  The body may already have arrived along with the header.  Poll briefly for anything more.
//  A -2 return simply means nothing further arrived, which is not an error here.
Dim pollTimeoutMs As Int32
pollTimeoutMs = 200
Dim numBytesRead As Int32
numBytesRead = ssh.ChannelPoll(channelNum,pollTimeoutMs)
If (numBytesRead = -1) Then
    System.DebugLog(ssh.LastErrorText)
    Return
End If

Dim htmlBody As String
htmlBody = ssh.GetReceivedText(channelNum,"utf-8")
If (ssh.LastMethodSuccess = False) Then
    System.DebugLog(ssh.LastErrorText)
    Return
End If

System.DebugLog("---- HTML BODY ----")
System.DebugLog(htmlBody)

success = ssh.ChannelSendClose(channelNum)
If (success = False) Then
    System.DebugLog(ssh.LastErrorText)
    Return
End If

ssh.Disconnect