Visual FoxPro

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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LOCAL lnSuccess
LOCAL loSftp
LOCAL lnPort
LOCAL lcPassword
LOCAL lcHandle
LOCAL lnOffset
LOCAL lnNumBytes
LOCAL lcText

lnSuccess = 0

*  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.

loSftp = CreateObject('Chilkat.SFtp')

*  Connect, authenticate, and initialize the SFTP subsystem.
lnPort = 22
lnSuccess = loSftp.Connect("sftp.example.com",lnPort)
IF (lnSuccess = 0) THEN
    ? loSftp.LastErrorText
    RELEASE loSftp
    CANCEL
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.
lcPassword = "mySshPassword"

lnSuccess = loSftp.AuthenticatePw("mySshLogin",lcPassword)
IF (lnSuccess = 0) THEN
    ? loSftp.LastErrorText
    RELEASE loSftp
    CANCEL
ENDIF

lnSuccess = loSftp.InitializeSftp()
IF (lnSuccess = 0) THEN
    ? loSftp.LastErrorText
    RELEASE loSftp
    CANCEL
ENDIF

lcHandle = loSftp.OpenFile("subdir/record.dat","readOnly","openExisting")
IF (loSftp.LastMethodSuccess = 0) THEN
    ? loSftp.LastErrorText
    RELEASE loSftp
    CANCEL
ENDIF

*  Read 5 bytes starting at byte offset 10, without first reading the bytes before it.
lnOffset = 10
lnNumBytes = 5
lcText = loSftp.ReadFileText32(lcHandle,lnOffset,lnNumBytes,"utf-8")
IF (loSftp.LastMethodSuccess = 0) THEN
    ? loSftp.LastErrorText
    RELEASE loSftp
    CANCEL
ENDIF

? lcText

lnSuccess = loSftp.CloseHandle(lcHandle)
IF (lnSuccess = 0) THEN
    ? loSftp.LastErrorText
    RELEASE loSftp
    CANCEL
ENDIF

loSftp.Disconnect()

RELEASE loSftp