PureBasic

Read Data from an SSH Channel

Demonstrates the Chilkat Ssh.ChannelRead method, which reads incoming SSH channel messages. The only argument is the channel number; the ReadTimeoutMs property limits how long it waits. Received data is appended to the channel's receive buffer, then retrieved with a GetReceived... method.

The integer return value is -1 on error, -2 if nothing arrived before the timeout, 0 if EOF or channel close was processed, or — when greater than 0 — the total bytes currently buffered for the channel (not the bytes newly received by this call).

Background: SSH reading is a two-step pattern that trips people up at first: the Channel* read/poll methods move bytes from the network into an internal per-channel buffer, and a separate GetReceived... call hands that buffer to your code. A positive return is therefore a buffer total, not a count of what this call fetched. Note that a 0 return means EOF or close — buffered data can still remain and should be drained.

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IncludeFile "CkSsh.pb"

Procedure ChilkatExample()

    success.i = 0

    ;  Demonstrates the Ssh.ChannelRead method, which reads incoming SSH channel messages.  The only
    ;  argument is the channel number.  The ReadTimeoutMs property limits how long it waits.

    ssh.i = CkSsh::ckCreate()
    If ssh.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    sshPort.i = 22
    success = CkSsh::ckConnect(ssh,"ssh.example.com",sshPort)
    If success = 0
        Debug CkSsh::ckLastErrorText(ssh)
        CkSsh::ckDispose(ssh)
        ProcedureReturn
    EndIf

    ;  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.
    password.s = "mySshPassword"

    success = CkSsh::ckAuthenticatePw(ssh,"mySshLogin",password)
    If success = 0
        Debug CkSsh::ckLastErrorText(ssh)
        CkSsh::ckDispose(ssh)
        ProcedureReturn
    EndIf

    channelNum.i = CkSsh::ckOpenSessionChannel(ssh)
    If channelNum < 0
        Debug CkSsh::ckLastErrorText(ssh)
        CkSsh::ckDispose(ssh)
        ProcedureReturn
    EndIf

    ;  Start a shell WITHOUT requesting a PTY.  Without a PTY the shell sees it is connected to a
    ;  raw data pipe and enters non-interactive mode: it suppresses the command prompt, does not
    ;  echo typed commands back, and skips interactive login scripts.  The output is therefore
    ;  clean and easily parseable -- but because no prompt is ever sent, code must not wait for
    ;  one.  Instead, have each command print a predictable marker, or wait for EOF / channel close.
    success = CkSsh::ckSendReqShell(ssh,channelNum)
    If success = 0
        Debug CkSsh::ckLastErrorText(ssh)
        CkSsh::ckDispose(ssh)
        ProcedureReturn
    EndIf

    success = CkSsh::ckChannelSendString(ssh,channelNum,"uname -a" + Chr(10),"utf-8")
    If success = 0
        Debug CkSsh::ckLastErrorText(ssh)
        CkSsh::ckDispose(ssh)
        ProcedureReturn
    EndIf

    ;  The return value is: -1 on error, -2 if nothing arrived before the timeout, 0 if EOF or
    ;  channel close was processed, or the total number of buffered bytes when greater than 0.
    result.i = CkSsh::ckChannelRead(ssh,channelNum)
    If result = -1
        Debug CkSsh::ckLastErrorText(ssh)
        CkSsh::ckDispose(ssh)
        ProcedureReturn
    EndIf

    If result = -2
        Debug "No channel data arrived before the timeout."
    EndIf

    If result = 0
        Debug "EOF or channel close was processed.  Buffered data may still remain."
    EndIf

    If result > 0
        Debug "Total bytes buffered: " + Str(result)
    EndIf

    output.s = CkSsh::ckGetReceivedText(ssh,channelNum,"utf-8")
    If CkSsh::ckLastMethodSuccess(ssh) = 0
        Debug CkSsh::ckLastErrorText(ssh)
        CkSsh::ckDispose(ssh)
        ProcedureReturn
    EndIf

    Debug output

    CkSsh::ckDisconnect(ssh)


    CkSsh::ckDispose(ssh)


    ProcedureReturn
EndProcedure