Delphi DLL

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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var
success: Boolean;
sftp: HCkSFtp;
port: Integer;
password: PWideChar;
handle: PWideChar;
offset: Integer;
numBytes: Integer;
text: PWideChar;

begin
success := False;

//  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.

sftp := CkSFtp_Create();

//  Connect, authenticate, and initialize the SFTP subsystem.
port := 22;
success := CkSFtp_Connect(sftp,'sftp.example.com',port);
if (success = False) then
  begin
    Memo1.Lines.Add(CkSFtp__lastErrorText(sftp));
    Exit;
  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.
password := 'mySshPassword';

success := CkSFtp_AuthenticatePw(sftp,'mySshLogin',password);
if (success = False) then
  begin
    Memo1.Lines.Add(CkSFtp__lastErrorText(sftp));
    Exit;
  end;

success := CkSFtp_InitializeSftp(sftp);
if (success = False) then
  begin
    Memo1.Lines.Add(CkSFtp__lastErrorText(sftp));
    Exit;
  end;

handle := CkSFtp__openFile(sftp,'subdir/record.dat','readOnly','openExisting');
if (CkSFtp_getLastMethodSuccess(sftp) = False) then
  begin
    Memo1.Lines.Add(CkSFtp__lastErrorText(sftp));
    Exit;
  end;

//  Read 5 bytes starting at byte offset 10, without first reading the bytes before it.
offset := 10;
numBytes := 5;
text := CkSFtp__readFileText32(sftp,handle,offset,numBytes,'utf-8');
if (CkSFtp_getLastMethodSuccess(sftp) = False) then
  begin
    Memo1.Lines.Add(CkSFtp__lastErrorText(sftp));
    Exit;
  end;
Memo1.Lines.Add(text);

success := CkSFtp_CloseHandle(sftp,handle);
if (success = False) then
  begin
    Memo1.Lines.Add(CkSFtp__lastErrorText(sftp));
    Exit;
  end;

CkSFtp_Disconnect(sftp);

CkSFtp_Dispose(sftp);