PureBasic

Check Whether the Last SFTP Read Failed

Demonstrates the Chilkat SFtp.LastReadFailed method, which returns whether the most recent read for a handle failed. The only argument is the handle. A normal end-of-file is not a failure.

Background: A chunked read loop needs to tell three outcomes apart: more data, a clean end-of-file, and an actual error such as a dropped connection or a revoked handle. LastReadFailed isolates the error case — it is false on a normal EOF read (which succeeds with zero bytes) and true for an empty, malformed, or already-closed handle — so the loop can stop cleanly on EOF but bail out with an error message on a genuine failure.

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IncludeFile "CkBinData.pb"
IncludeFile "CkSFtp.pb"

Procedure ChilkatExample()

    success.i = 0

    ;  Demonstrates the SFtp.LastReadFailed method, which returns whether the most recent read for a
    ;  handle failed.  The only argument is the handle.  A normal end-of-file is NOT a failure.

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

    ;  Connect, authenticate, and initialize the SFTP subsystem.
    port.i = 22
    success = CkSFtp::ckConnect(sftp,"sftp.example.com",port)
    If success = 0
        Debug CkSFtp::ckLastErrorText(sftp)
        CkSFtp::ckDispose(sftp)
        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 = CkSFtp::ckAuthenticatePw(sftp,"mySshLogin",password)
    If success = 0
        Debug CkSFtp::ckLastErrorText(sftp)
        CkSFtp::ckDispose(sftp)
        ProcedureReturn
    EndIf

    success = CkSFtp::ckInitializeSftp(sftp)
    If success = 0
        Debug CkSFtp::ckLastErrorText(sftp)
        CkSFtp::ckDispose(sftp)
        ProcedureReturn
    EndIf

    handle.s = CkSFtp::ckOpenFile(sftp,"subdir/data.txt","readOnly","openExisting")
    If CkSFtp::ckLastMethodSuccess(sftp) = 0
        Debug CkSFtp::ckLastErrorText(sftp)
        CkSFtp::ckDispose(sftp)
        ProcedureReturn
    EndIf

    reading.i = 1
    chunkSize.i = 4096
    bd.i = CkBinData::ckCreate()
    If bd.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    While reading
        success = CkSFtp::ckReadFileBd(sftp,handle,chunkSize,bd)

        ;  Distinguish an actual read failure from a normal EOF.  On EOF the read succeeds, returns
        ;  zero bytes, and LastReadFailed is 0.
        If CkSFtp::ckLastReadFailed(sftp,handle)
            Debug "Read failed: " + CkSFtp::ckLastErrorText(sftp)
            CkSFtp::ckDispose(sftp)
            CkBinData::ckDispose(bd)
            ProcedureReturn
        EndIf

        reading = Not CkSFtp::ckEof(sftp,handle)
    Wend

    success = CkSFtp::ckCloseHandle(sftp,handle)
    If success = 0
        Debug CkSFtp::ckLastErrorText(sftp)
        CkSFtp::ckDispose(sftp)
        CkBinData::ckDispose(bd)
        ProcedureReturn
    EndIf

    Debug "Read " + Str(CkBinData::ckNumBytes(bd)) + " bytes with no read failures."

    CkSFtp::ckDisconnect(sftp)


    CkSFtp::ckDispose(sftp)
    CkBinData::ckDispose(bd)


    ProcedureReturn
EndProcedure