Xbase++

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 nSuccess
LOCAL oSftp
LOCAL nPort
LOCAL cPassword
LOCAL cHandle
LOCAL nOffset
LOCAL nNumBytes
LOCAL cText

nSuccess := 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.

oSftp := CreateObject("Chilkat.SFtp")

//  Connect, authenticate, and initialize the SFTP subsystem.
nPort := 22
nSuccess := oSftp:Connect("sftp.example.com", nPort)
IF (nSuccess == 0)
    ? oSftp:LastErrorText
    oSftp:destroy()
    RETURN
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.
cPassword := "mySshPassword"

nSuccess := oSftp:AuthenticatePw("mySshLogin", cPassword)
IF (nSuccess == 0)
    ? oSftp:LastErrorText
    oSftp:destroy()
    RETURN
ENDIF

nSuccess := oSftp:InitializeSftp()
IF (nSuccess == 0)
    ? oSftp:LastErrorText
    oSftp:destroy()
    RETURN
ENDIF

cHandle := oSftp:OpenFile("subdir/record.dat", "readOnly", "openExisting")
IF (oSftp:LastMethodSuccess == 0)
    ? oSftp:LastErrorText
    oSftp:destroy()
    RETURN
ENDIF

//  Read 5 bytes starting at byte offset 10, without first reading the bytes before it.
nOffset := 10
nNumBytes := 5
cText := oSftp:ReadFileText32(cHandle, nOffset, nNumBytes, "utf-8")
IF (oSftp:LastMethodSuccess == 0)
    ? oSftp:LastErrorText
    oSftp:destroy()
    RETURN
ENDIF

? cText

nSuccess := oSftp:CloseHandle(cHandle)
IF (nSuccess == 0)
    ? oSftp:LastErrorText
    oSftp:destroy()
    RETURN
ENDIF

oSftp:Disconnect()

oSftp:destroy()