There are not many good TFTP server examples out there, so I wrote this example of a multi-thredded TFTP Server, using Indy components.

There are few good examples of TFTP servers, so I
wrote this complete server as an example.

If works like a Secure TFTP server, since it only
allows uploads/downloads from a specific directory.

The example assumes that you open a new project with
a new form (Form1), and drop one TFTP Server and TFTP
Client on the form, and two buttons.

The source below can be copied as such. Enjoy.

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unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, IdBaseComponent, IdComponent, IdUDPBase, IdUDPServer,
  IdTrivialFTPServer, StdCtrls, IdUDPClient, IdTrivialFTP;

type
  TForm1 = class(TForm)
    IdTrivialFTPServer1: TIdTrivialFTPServer;
    IdTrivialFTP1: TIdTrivialFTP;
    Button1: TButton;
    Button2: TButton;
    procedure FormCreate(Sender: TObject);
    procedure IdTrivialFTPServer1ReadFile(Sender: TObject;
      var FileName: String; const PeerInfo: TPeerInfo;
      var GrantAccess: Boolean; var AStream: TStream;
      var FreeStreamOnComplete: Boolean);
    procedure IdTrivialFTPServer1TransferComplete(Sender: TObject;
      const Success: Boolean; const PeerInfo: TPeerInfo; AStream: TStream;
      const WriteOperation: Boolean);
    procedure IdTrivialFTPServer1WriteFile(Sender: TObject;
      var FileName: String; const PeerInfo: TPeerInfo;
      var GrantAccess: Boolean; var AStream: TStream;
      var FreeStreamOnComplete: Boolean);
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
    TFTPPath              : String;
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
     IdTrivialFTPServer1.ThreadedEvent := True;
     IdTrivialFTPServer1.Active := True;
     { Set the path to where the files will be stored/retreived }
     TFTPPath := IncludeTrailingPathDelimiter('C:\Temp');
end;

procedure TForm1.IdTrivialFTPServer1ReadFile(Sender: TObject;
  var FileName: String; const PeerInfo: TPeerInfo;
  var GrantAccess: Boolean; var AStream: TStream;
  var FreeStreamOnComplete: Boolean);
Var
   FS : TFileStream;
begin
     FreeStreamOnComplete := True;
     Try
        { Convert UNIX style filenames to WINDOWS style }
        While Pos('/',Filename)<>0 do Filename[Pos('/',Filename)] := '\';
        { Assure that the filename DOES NOT CONTAIN any path information }
        Filename := ExtractFileName( Filename );
        { Check if file exists }
        If FileExists( TFTPPath+Filename ) then
        Begin
          { Open file in READ ONLY mode }
          FS := TFileStream.Create( TFTPPath+Filename,
                                    fmOpenRead OR fmShareDenyWrite );
          { Assign stream to variable }
          AStream := FS;
          { Set parameters }
          GrantAccess := True;
        End Else
        Begin
          GrantAccess := False;
        End;
     Except
        { On errors, deny access }
        GrantAccess := False;
        If Assigned(FS) then FreeAndNil( FS );
     End;
end;

procedure TForm1.IdTrivialFTPServer1WriteFile(Sender: TObject;
  var FileName: String; const PeerInfo: TPeerInfo;
  var GrantAccess: Boolean; var AStream: TStream;
  var FreeStreamOnComplete: Boolean);
Var
   FS : TFileStream;
begin
     Try
        { Convert UNIX style filenames to WINDOWS style }
        While Pos('/',Filename)<>0 do Filename[Pos('/',Filename)] := '\';
        { Assure that the filename DOES NOT CONTAIN any path information }
        Filename := ExtractFileName( Filename );
        { Open file in WRITE ONLY mode }
        FS := TFileStream.Create( TFTPPath+Filename,
                                  fmCreate OR fmShareExclusive );
        { Copy all the data }
        AStream := FS;
        { Set parameters }
        FreeStreamOnComplete := True;
        GrantAccess := True;
     Except
        { On errors, deny access }
        GrantAccess := False;
        If Assigned(FS) then FreeAndNil( FS );
     End;
end;

procedure TForm1.IdTrivialFTPServer1TransferComplete(Sender: TObject;
  const Success: Boolean; const PeerInfo: TPeerInfo; AStream: TStream;
  const WriteOperation: Boolean);
begin
     // Success = TRUE if the read/write operation was successfull
     // WriteOperation = TRUE if the client SENT a file to the server
     Try
        { Close the FileStream }
        If Assigned(AStream) then FreeAndNil(AStream);
     Except
     End;
end;

// Example of how to DOWNLOAD a file from the server
procedure TForm1.Button1Click(Sender: TObject);
Var
   ST : TMemoryStream;
begin
     ST := TMemoryStream.Create;
     IdTrivialFTP1.Get('testfile.dat',ST);
     If Assigned(ST) then
     begin
          ShowMessage('Filesize='+IntToStr(ST.Size));
          FreeAndNil(ST);
     end;
end;

// Example of how to UPLOAD a file to the server
procedure TForm1.Button2Click(Sender: TObject);
Var
   ST : TMemoryStream;
   I  : Integer;
   S  : String;
begin
     { Create stream }
     ST := TMemoryStream.Create;
     { Initialize data }
     S := 'This is a test file. It whould appear in the '+
          'TFTP Server''s upload directory.'+#13#10;
     { Store in stream }
     ST.Write( S[1], Length(S) );
     ST.Position := 0;
     { Send Stream to TFTP Server }
     IdTrivialFTP1.Put(ST,'textfile.txt');
     { Free Stream }
     If Assigned(ST) then FreeAndNil(ST);
     { Show a dialog }
     ShowMessage('Done!');
end;

end.