DataFlex

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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DataFlex

Use ChilkatAx-win32.pkg

Procedure Test
    Boolean iSuccess
    Handle hoSftp
    Integer iPort
    String sPassword
    String sHandle
    Boolean iReading
    Integer iChunkSize
    Variant vBd
    Handle hoBd
    String sTemp1
    Integer iTemp1
    Boolean bTemp1

    Move False To iSuccess

    //  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.

    Get Create (RefClass(cComChilkatSFtp)) To hoSftp
    If (Not(IsComObjectCreated(hoSftp))) Begin
        Send CreateComObject of hoSftp
    End

    //  Connect, authenticate, and initialize the SFTP subsystem.
    Move 22 To iPort
    Get ComConnect Of hoSftp "sftp.example.com" iPort To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoSftp To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    //  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.
    Move "mySshPassword" To sPassword

    Get ComAuthenticatePw Of hoSftp "mySshLogin" sPassword To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoSftp To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    Get ComInitializeSftp Of hoSftp To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoSftp To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    Get ComOpenFile Of hoSftp "subdir/data.txt" "readOnly" "openExisting" To sHandle
    Get ComLastMethodSuccess Of hoSftp To bTemp1
    If (bTemp1 = False) Begin
        Get ComLastErrorText Of hoSftp To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    Move True To iReading
    Move 4096 To iChunkSize
    Get Create (RefClass(cComChilkatBinData)) To hoBd
    If (Not(IsComObjectCreated(hoBd))) Begin
        Send CreateComObject of hoBd
    End
    While iReading
        Get pvComObject of hoBd to vBd
        Get ComReadFileBd Of hoSftp sHandle iChunkSize vBd To iSuccess

        //  Distinguish an actual read failure from a normal EOF.  On EOF the read succeeds, returns
        //  zero bytes, and LastReadFailed is False.
        Get ComLastReadFailed Of hoSftp sHandle To bTemp1
        If (bTemp1) Begin
            Get ComLastErrorText Of hoSftp To sTemp1
            Showln "Read failed: " sTemp1
            Procedure_Return
        End

        Get ComEof Of hoSftp sHandle To bTemp1
        Move (Not bTemp1) To iReading
    Loop

    Get ComCloseHandle Of hoSftp sHandle To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoSftp To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    Get ComNumBytes Of hoBd To iTemp1
    Showln "Read " iTemp1 " bytes with no read failures."

    Send ComDisconnect To hoSftp


End_Procedure