PureBasic

SSH to a Cisco Switch - Processing "More" Responses

Demonstrates connecting to a Cisco switch, entering privileged mode with the ena command, and running a command whose response is paged. Each page ends with --More-- and requires a SPACE character to request the next page.

Note: QuickShell allocates a PTY, which is what a network device console expects. The device presents an interactive prompt, and each command's output is read up to the next prompt.

Background: Paged output is the console equivalent of a pager like more, and a client must reproduce the keypress a human would make. Matching a set of patterns is what makes this tractable: each read ends either at the device prompt (output complete) or at --More-- (another page waiting), and the code branches accordingly. Note the prompt pattern includes the device name rather than a bare #, because that character also appears inside configuration text and would otherwise match far too early.

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IncludeFile "CkStringBuilder.pb"
IncludeFile "CkSsh.pb"
IncludeFile "CkStringArray.pb"

Procedure ChilkatExample()

    success.i = 0

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

    ;  Demonstrates connecting to a Cisco switch, entering privileged mode, and running a command
    ;  whose response is paged -- each page ends with "--More--" and requires a SPACE character to
    ;  request the next page.

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

    port.i = 22
    success = CkSsh::ckConnect(ssh,"172.16.16.100",port)
    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::ckQuickShell(ssh)
    If channelNum < 0
        Debug CkSsh::ckLastErrorText(ssh)
        CkSsh::ckDispose(ssh)
        ProcedureReturn
    EndIf

    ;  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.
    CkSsh::setCkReadTimeoutMs(ssh, 15000)

    caseSensitive.i = 1

    ;  In unprivileged mode the switch prompt ends with ">".
    success = CkSsh::ckChannelReceiveUntilMatch(ssh,channelNum,">","utf-8",caseSensitive)
    If success = 0
        Debug CkSsh::ckLastErrorText(ssh)
        CkSsh::ckDispose(ssh)
        ProcedureReturn
    EndIf

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

    Debug received

    ;  Send "ena" to enter privileged mode.  Cisco devices expect a bare CR to terminate a command.
    success = CkSsh::ckChannelSendString(ssh,channelNum,"ena" + Chr(13),"utf-8")
    If success = 0
        Debug CkSsh::ckLastErrorText(ssh)
        CkSsh::ckDispose(ssh)
        ProcedureReturn
    EndIf

    success = CkSsh::ckChannelReceiveUntilMatch(ssh,channelNum,"Password:","utf-8",caseSensitive)
    If success = 0
        Debug CkSsh::ckLastErrorText(ssh)
        CkSsh::ckDispose(ssh)
        ProcedureReturn
    EndIf

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

    Debug received

    ;  The enable password is separate from the login password, and likewise should come from a
    ;  secure source rather than being hard-coded.
    enablePassword.s = "myEnablePassword"
    success = CkSsh::ckChannelSendString(ssh,channelNum,enablePassword,"utf-8")
    If success = 0
        Debug CkSsh::ckLastErrorText(ssh)
        CkSsh::ckDispose(ssh)
        ProcedureReturn
    EndIf

    success = CkSsh::ckChannelSendString(ssh,channelNum,Chr(13),"utf-8")
    If success = 0
        Debug CkSsh::ckLastErrorText(ssh)
        CkSsh::ckDispose(ssh)
        ProcedureReturn
    EndIf

    ;  In privileged mode the prompt ends with "#" instead of ">".
    success = CkSsh::ckChannelReceiveUntilMatch(ssh,channelNum,"#","utf-8",caseSensitive)
    If success = 0
        Debug CkSsh::ckLastErrorText(ssh)
        CkSsh::ckDispose(ssh)
        ProcedureReturn
    EndIf

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

    Debug received

    ;  Run a command whose output is delivered a page at a time.
    success = CkSsh::ckChannelSendString(ssh,channelNum,"show running-config" + Chr(13),"utf-8")
    If success = 0
        Debug CkSsh::ckLastErrorText(ssh)
        CkSsh::ckDispose(ssh)
        ProcedureReturn
    EndIf

    ;  Each read ends either at the device prompt (output complete) or at "--More--" (another page
    ;  is waiting).  Match the full prompt rather than a bare "#", because "#" also appears inside
    ;  configuration text and would match too early.
    saMatch.i = CkStringArray::ckCreate()
    If saMatch.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkStringArray::ckAppend(saMatch,"MySwitchName#")
    CkStringArray::ckAppend(saMatch,"--More--")

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

    moreComing.i = 1

    While moreComing
        success = CkSsh::ckChannelReceiveUntilMatchN(ssh,channelNum,saMatch,"utf-8",caseSensitive)
        If success = 0
            Debug CkSsh::ckLastErrorText(ssh)
            CkSsh::ckDispose(ssh)
            CkStringArray::ckDispose(saMatch)
            CkStringBuilder::ckDispose(sbReceived)
            ProcedureReturn
        EndIf

        CkStringBuilder::ckClear(sbReceived)
        pageText.s = CkSsh::ckGetReceivedText(ssh,channelNum,"utf-8")
        If CkSsh::ckLastMethodSuccess(ssh) = 0
            Debug CkSsh::ckLastErrorText(ssh)
            CkSsh::ckDispose(ssh)
            CkStringArray::ckDispose(saMatch)
            CkStringBuilder::ckDispose(sbReceived)
            ProcedureReturn
        EndIf

        CkStringBuilder::ckAppend(sbReceived,pageText)
        Debug pageText

        ;  If this page ended with "--More--", send a SPACE to request the next page.
        moreComing = CkStringBuilder::ckContains(sbReceived,"--More--",caseSensitive)
        If moreComing
            success = CkSsh::ckChannelSendString(ssh,channelNum," ","utf-8")
            If success = 0
                Debug CkSsh::ckLastErrorText(ssh)
                CkSsh::ckDispose(ssh)
                CkStringArray::ckDispose(saMatch)
                CkStringBuilder::ckDispose(sbReceived)
                ProcedureReturn
            EndIf

        EndIf

    Wend

    CkSsh::ckDisconnect(ssh)


    CkSsh::ckDispose(ssh)
    CkStringArray::ckDispose(saMatch)
    CkStringBuilder::ckDispose(sbReceived)


    ProcedureReturn
EndProcedure