A idéia é receber um fluxo continuo de texto de um servidor WEB e imprimir sempre que preciso.

httpstream.dpr

program httpstream;

uses
  Forms,
  Ustream in 'Ustream.pas' {Fstream};

{$R *.res}

begin
  Application.Initialize;
  Application.CreateForm(TFstream, Fstream);
  Application.Run;
end.

ustream.dfm

object Fstream: TFstream
  Left = 332
  Top = 118
  Width = 332
  Height = 500
  Caption = 'HTTP Stream '
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'MS Sans Serif'
  Font.Style = []
  OldCreateOrder = False
  PixelsPerInch = 96
  TextHeight = 13
  object GroupBox1: TGroupBox
    Left = 0
    Top = 40
    Width = 321
    Height = 425
    Caption = 'Imprimindo'
    TabOrder = 0
    object Memo1: TMemo
      Left = 2
      Top = 15
      Width = 317
      Height = 408
      Align = alClient
      Lines.Strings = (
        'Memo1')
      TabOrder = 0
    end
  end
  object Button1: TButton
    Left = 8
    Top = 8
    Width = 75
    Height = 25
    Caption = 'Button1'
    TabOrder = 1
    OnClick = Button1Click
  end
  object Edit1: TEdit
    Left = 120
    Top = 8
    Width = 65
    Height = 21
    ReadOnly = True
    TabOrder = 2
    Text = 'Edit1'
  end
  object IdHTTP2: TIdHTTP
    MaxLineAction = maException
    ReadTimeout = 0
    AuthRetries = 0
    AllowCookies = True
    ProxyParams.BasicAuthentication = False
    ProxyParams.ProxyPort = 0
    Request.ContentLength = -1
    Request.ContentRangeEnd = 0
    Request.ContentRangeStart = 0
    Request.ContentType = 'text/html'
    Request.Accept = 'text/html, */*'
    Request.BasicAuthentication = False
    Request.Host = 'localhost'
    Request.UserAgent = 'Mozilla/3.0 (compatible; Indy Library) (CSAT)'
    HTTPOptions = [hoForceEncodeParams]
    Left = 88
    Top = 8
  end
end

ustream.pas

unit Ustream;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, IdIOHandler, IdIOHandlerStream, IdBaseComponent,
  IdComponent, IdTCPConnection, IdTCPClient, IdHTTP;

type
  TFstream = class(TForm)
    IdHTTP2: TIdHTTP;
    GroupBox1: TGroupBox;
    Memo1: TMemo;
    Button1: TButton;
    Edit1: TEdit;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Fstream: TFstream;

implementation

uses DateUtils;

{$R *.dfm}

procedure TFstream.Button1Click(Sender: TObject);
var
  input:      TStringStream;
  output:     TMemoryStream;
  postStr:    string;
  postRespStr:string;
begin
  input   :=TStringStream.Create('');
  output  :=TMemoryStream.Create;



    // no local do número informado para id, substituir com o codigo do posto
  // mesmo passando o login e senha é bom conferir o codigo do posto também
  postStr:='Login=painel&password=0b82&id=1';
  With IdHTTP2 do
  begin

    Request.UserAgent           :='CSAT Browser - v0.1 (Nothing Compatible)';
    Request.Accept              :='text/html';
    Request.AcceptLanguage      :='pt-BR;q=0.7,en;q=0.3';
    Request.AcceptEncoding      :='gzip,deflate';
    Request.AcceptCharset       :='utf-8;q=0.7,*;q=0.7';
    Request.BasicAuthentication := False;
    Request.Connection          :='keep-alive';
    //  IdHTTP2.Request.referer:='http://???????????';
    Request.ContentType         :='application/x-www-form-urlencoded';
    Request.ContentLength       :=length(postStr);


    // Headers are only example too...
    //Request.CustomHeaders.Add('POST /cps2_admin/senhas HTTP/1.1');

    Request.CustomHeaders.Add('Keep-Alive: 300');

    Request.Host:= 'localhost';

  end;


  input.writestring(postStr);

  IdHTTP2.post('http://localhost/cps2_admin/senhas',input,output);

{
apartir deste ponto após o post se confirmar como 200, entro num loop infinito
pegando o conteudo do output e trando ele e enviando para a impressora sempre que preciso.
}
  Edit1.Text := IntToStr(IdHTTP2.ResponseCode);

{}
  output.WriteComponent(Memo1);
{}

  Memo1.Lines.Add(IdHTTP2.Response.ResponseText);

  input.free;
  output.free;
//  MemoryStream.Free;

end;

end.


{
Dicas de impressão:
http://www.tecnobyte.com.br/dica3.html


Verificar se está conectado:
http://www.tecnobyte.com.br/dica5.html#dica84

Outras Dicas:
http://www.efg2.com/Lab/Library/Delphi/IO/StreamIO.htm



}

Veja um exemplo em perl no link: https://gist.github.com/923532