DataFlex

Read Text at a 32-bit Offset from a Remote SFTP File

Demonstrates the Chilkat SFtp.ReadFileText32 method, which reads up to a number of bytes from a specific 32-bit byte offset of an open handle and decodes them to text. The arguments are the handle, the offset, the maximum number of bytes, and the charset.

Background: Reading from an explicit offset lets you fetch just the part of a file you need — a header, a record at a known position, a slice of a large log — without downloading everything before it. As with offset writes, the offset counts bytes rather than characters, so it must respect the encoded width of any multibyte content.

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Use ChilkatAx-win32.pkg

Procedure Test
    Boolean iSuccess
    Handle hoSftp
    Integer iPort
    String sPassword
    String sHandle
    Integer iOffset
    Integer iNumBytes
    String sText
    String sTemp1
    Boolean bTemp1

    Move False To iSuccess

    //  Demonstrates the SFtp.ReadFileText32 method, which reads up to a number of bytes from a
    //  specific 32-bit byte offset of an open handle and decodes them to text.  The 1st argument is
    //  the handle, the 2nd is the offset, the 3rd is the maximum number of bytes, and the 4th is the
    //  charset.

    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/record.dat" "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

    //  Read 5 bytes starting at byte offset 10, without first reading the bytes before it.
    Move 10 To iOffset
    Move 5 To iNumBytes
    Get ComReadFileText32 Of hoSftp sHandle iOffset iNumBytes "utf-8" To sText
    Get ComLastMethodSuccess Of hoSftp To bTemp1
    If (bTemp1 = False) Begin
        Get ComLastErrorText Of hoSftp To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    Showln sText

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

    Send ComDisconnect To hoSftp


End_Procedure