SFTP Client sgcIndy Delphi Component

Secure file transfer remains a cornerstone of enterprise integration. Whether you are exchanging data with banking partners, synchronizing files with remote servers, or automating deployment pipelines, SFTP (SSH File Transfer Protocol) is the industry standard for moving files securely over untrusted networks.

The sgcIndy package includes TIdSFTPClient — a native Delphi SFTP client component that runs over SSH without requiring external command-line tools or third-party executables. It supports file upload and download, directory management, symbolic links, file attributes, progress tracking, and modern cryptographic algorithms — all through a clean, event-driven API.

This article covers the full feature set and provides ready-to-use Delphi code for the most common SFTP operations.

Key Features

Quick Start — Connect and Download a File

A minimal example that connects to a remote server, downloads a file, and disconnects.

var
  oSFTP: TIdSFTPClient;
begin
  oSFTP := TIdSFTPClient.Create(nil);
  Try
    oSFTP.Host := 'sftp.example.com';
    oSFTP.Port := 22;
    oSFTP.Authentication.Username := 'deploy';
    oSFTP.Authentication.Password := 'secret';
    oSFTP.Connect;

    // Download a file
    oSFTP.Get('/data/report.csv', 'C:\local\report.csv');

    oSFTP.Disconnect;
  Finally
    oSFTP.Free;
  End;
end;

Authentication

The component supports three authentication methods. All three are enabled by default — the client and server negotiate the most appropriate method automatically.

Password Authentication

oSFTP.Authentication.Username := 'admin';
oSFTP.Authentication.Password := 'secret';

Public Key Authentication

oSFTP.Authentication.Username := 'deploy';
oSFTP.Authentication.PrivateKeyFile := 'C:\keys\id_rsa';
oSFTP.Authentication.PublicKeyFile := 'C:\keys\id_rsa.pub';
oSFTP.Authentication.Passphrase := 'keypassphrase';

Host Key Verification

Verify the server's identity by inspecting the host key fingerprint in the OnSSHHostKey event.

oSFTP.OnSSHHostKey := OnHostKey;

procedure TForm1.OnHostKey(Sender: TObject;
  const aHostKeyType, aFingerprint: string;
  var aAction: TIdSSHHostKeyVerification);
begin
  // Verify fingerprint against known hosts
  if aFingerprint = 'SHA256:xyzABC123...' then
    aAction := sshHostKeyAccept
  else
    aAction := sshHostKeyReject;
end;

File Operations

Upload & Download

// Upload a file
oSFTP.Put('C:\local\data.zip', '/uploads/data.zip');

// Download a file
oSFTP.Get('/reports/monthly.pdf', 'C:\local\monthly.pdf');

// Upload from a stream
oSFTP.Put(oMemoryStream, '/uploads/stream-data.bin');

// Download to a stream
oSFTP.Get('/data/export.csv', oFileStream);

String Convenience Methods

// Read a remote file into a string
vContent := oSFTP.GetFileAsString('/config/settings.json');

// Write a string to a remote file
oSFTP.PutFileFromString('{"key":"value"}', '/config/settings.json');

Delete, Rename & Symlinks

// Delete a remote file
oSFTP.Delete('/tmp/old-file.log');

// Rename / move a file
oSFTP.Rename('/data/temp.csv', '/data/final.csv');

// Create a symbolic link
oSFTP.Symlink('/data/final.csv', '/data/latest.csv');

Directory Operations

// List directory contents with full metadata
var
  oItems: TIdSFTPDirectoryItems;
  i: Integer;
begin
  oItems := oSFTP.ListDirectory('/data');
  for i := 0 to Length(oItems) - 1 do
    WriteLn(oItems[i].Filename + ' - ' +
      IntToStr(oItems[i].Attrs.Size) + ' bytes');
end;

// Create and remove directories
oSFTP.MakeDirectory('/data/archive/2026');
oSFTP.RemoveDirectory('/data/temp');

// Get current working directory
vPath := oSFTP.GetCurrentDirectory;

// Resolve a path (follows symlinks, resolves . and ..)
vRealPath := oSFTP.RealPath('../data/../data/./file.txt');

File Attributes & Information

// Check existence
if oSFTP.FileExists('/data/report.csv') then
  WriteLn('File found');

if oSFTP.DirectoryExists('/data/archive') then
  WriteLn('Directory exists');

// Get file size
vSize := oSFTP.FileSize('/data/report.csv');

// Get full attributes (size, permissions, timestamps, UID/GID)
var
  oAttrs: TIdSFTPFileAttributes;
begin
  oAttrs := oSFTP.Stat('/data/report.csv');
  WriteLn('Size: ' + IntToStr(oAttrs.Size));
  WriteLn('Permissions: ' + IntToStr(oAttrs.Permissions));
end;

Transfer Progress & Cancellation

The OnSFTPProgress event fires during every file transfer, providing real-time tracking with the ability to cancel mid-transfer.

oSFTP.OnSFTPProgress := OnProgress;

procedure TForm1.OnProgress(Sender: TObject;
  const aFilename: string;
  aTransferred, aTotal: Int64;
  var Cancel: Boolean);
begin
  ProgressBar1.Max := aTotal;
  ProgressBar1.Position := aTransferred;
  Label1.Caption := Format('%s: %d / %d bytes',
    [aFilename, aTransferred, aTotal]);

  // Set Cancel := True to abort the transfer
  Cancel := FUserCancelled;
end;

Cryptographic Algorithm Configuration

The component supports modern cryptographic standards. The defaults are secure, but you can customize algorithm negotiation for compliance or interoperability requirements.

// Restrict to only the strongest algorithms
oSFTP.Algorithms.Ciphers := This email address is being protected from spambots. You need JavaScript enabled to view it.,aes256-ctr';
oSFTP.Algorithms.KexAlgorithms := 'curve25519-sha256';
oSFTP.Algorithms.MACs := 'hmac-sha2-256,hmac-sha2-512';

Complete Example

A production-ready example that connects with public key authentication, lists a directory, downloads a file with progress tracking, and handles errors.

uses
  IdSFTPClient, IdSSHClasses;

var
  oSFTP: TIdSFTPClient;
  oItems: TIdSFTPDirectoryItems;
  i: Integer;
begin
  oSFTP := TIdSFTPClient.Create(nil);
  Try
    // Connection
    oSFTP.Host := 'sftp.example.com';
    oSFTP.Port := 22;

    // Public key authentication
    oSFTP.Authentication.Username := 'deploy';
    oSFTP.Authentication.PrivateKeyFile := 'C:\keys\id_ed25519';

    // Events
    oSFTP.OnSFTPProgress := OnProgress;
    oSFTP.OnSFTPError := OnError;
    oSFTP.OnSSHHostKey := OnHostKey;

    // Connect
    oSFTP.Connect;

    // List remote directory
    oItems := oSFTP.ListDirectory('/data');
    for i := 0 to Length(oItems) - 1 do
      WriteLn(oItems[i].Filename);

    // Download file with progress
    oSFTP.Get('/data/backup.tar.gz', 'C:\backups\backup.tar.gz');

    // Disconnect
    oSFTP.Disconnect;
  Finally
    oSFTP.Free;
  End;
end;

Methods Reference