Leonardo's blog

Many times, I needed a way to let my Delphi/FPC applications to connect to an SSH server, execute some commands, and get its results. Now I'm publishing a simple class based on Synapse's TTelnetSend class to do exactly what I needed.

Required ingredients

First of all, you'll need to grab a copy of the latest version of Synapse, now, to connect to an SSH server, the connection must be established by using the SSL protocol, and Synapse allows that kind of connections with plugins that allow filtering the data through OpenSSL, CryptLib and StreamSecII. Here, I'll use CryptLib, so you'll have to get this compiled version of cl32.dll for Windows, if you need the library compiled for Linux search for it in your repository (or use Google).

Now, configure the search paths of your compiler to find both, Synapse source and cryptlib.pas, the wrapper for cl32.dll.

Introducing TSSHClient class

This is a simple class to let you connect to an SSH server in an Object Oriented way, its internal parts where found in the Synapse's newsgroups, tested and arranged in a class.

unit sshclient;

interface

uses
  tlntsend, ssl_openssl, ssl_openssl_lib, ssl_cryptlib;

type
  TSSHClient = class
  private
    FTelnetSend: TTelnetSend;
  public
    constructor Create(AHost, APort, AUser, APass: string);
    destructor Destroy; override;
    procedure SendCommand(ACommand: string);
    procedure LogOut;
    function ReceiveData: string;
    function LogIn: Boolean;
  end;

implementation

{ TSSHClient }

constructor TSSHClient.Create(AHost, APort, AUser, APass: string);
begin
  FTelnetSend := TTelnetSend.Create;
  FTelnetSend.TargetHost := AHost;
  FTelnetSend.TargetPort := APort;
  FTelnetSend.UserName := AUser;
  FTelnetSend.Password := APass;
end;

destructor TSSHClient.Destroy;
begin
  FTelnetSend.Free;
  inherited;
end;

function TSSHClient.LogIn: Boolean;
begin
  Result := FTelnetSend.SSHLogin;
end;

procedure TSSHClient.LogOut;
begin
  FTelnetSend.Logout;
end;

function TSSHClient.ReceiveData: string;
var
  lPos: Integer;
begin
  Result := '';
  lPos := 1;
  while FTelnetSend.Sock.CanRead(1000) or (FTelnetSend.Sock.WaitingData>0) do
  begin
    FTelnetSend.Sock.RecvPacket(1000);
    Result := Result + Copy(FTelnetSend.SessionLog, lPos, Length(FTelnetSend.SessionLog));
    lPos := Length(FTelnetSend.SessionLog)+1;
  end;
end;

procedure TSSHClient.SendCommand(ACommand: string);
begin
  FTelnetSend.Send(ACommand + #13);
end;

end.

A sample application

This is an example of how to execute an "df -h" command in an external SSH server, inspirated by a question in StackOverflow.

The example just connects to a server, execute the command and capture its output, just that.

program TestSSHClient;

{$APPTYPE CONSOLE}

uses
  sshclient;

var
  lSSh: TSSHClient;
begin
  lSSh := TSSHClient.Create('[TARGET_HOST_OR_IP_ADDRESS]', '[PORT]', '[USER]', '[PASSWORD]');
  if lSSh.LogIn then
  begin
    Writeln('Connected!.');
    (* Get welcome message *)
    Writeln(lSSh.ReceiveData);
    (* Send command *)
    lSSh.SendCommand('df -h');
    (* Receive results *)
    Writeln(lSSh.ReceiveData);
    lSSh.LogOut;
    Writeln('Logged out.');
  end
  else
    Writeln('Can''t connect.');
  lSSh.Free;
end.                            

Replace the words between '[' and ']' by the real ones and test it.

See you on my next post.