YOUSEFUL / DELPHI / COMPONENTS

`TAtlasTcpListener`

A listening TCP socket that accepts connections as TAtlasTcpTransport objects; the broker is built on it.

Class Unit Atlas.MqttTransport · Inherits TObject · Product Atlas MQTT

Description

TAtlasMqttBroker uses it to accept clients. Use it directly to write a scripted stand-in for a broker in a test: accept the client, then read and write packets byte by byte with TAtlasMqttCodec. IPv4 only. Errors raise EAtlasMqttTransportError.

Members

Member	Kind	What it does
`Create`	constructor	Binds and listens on `APort` (0 asks the system for a free port; read `Port` afterwards).
`Destroy`	destructor	Closes the listening socket.
`Close`	method	Stops listening.
`Accept`	method	Waits up to `TimeoutMs` milliseconds for a connection and returns it as a connected `TAtlasTcpTransport`, which the caller owns and frees.
`Port`	property	The port actually bound.

Constructors

`Create` constructor

constructor Create(APort: Word; LoopbackOnly: Boolean);

Binds and listens on APort (0 asks the system for a free port; read Port afterwards). LoopbackOnly True binds 127.0.0.1, False every IPv4 interface. Raises EAtlasMqttTransportError when the port cannot be bound.

Listener := TAtlasTcpListener.Create(0, True);  // any free port, this machine only

Destructors

`Destroy` destructor

destructor Destroy; override;

Closes the listening socket. Connections already accepted are separate objects and stay open.

Listener.Free;

Properties

`Port` property

property Port: Word read FPort;

The port actually bound.

Client.Port := Listener.Port;

Methods

`Close` method

procedure Close;

Stops listening. Safe to call from another thread and safe to call twice. Accept then returns nil.

Listener.Close;

`Accept` method

function Accept(TimeoutMs: Integer): TAtlasTcpTransport;

Waits up to TimeoutMs milliseconds for a connection and returns it as a connected TAtlasTcpTransport, which the caller owns and frees. Returns nil when nobody connected in time or the listener is closed.

Transport := Listener.Accept(1000);  // nil when nobody came

Examples

A stand-in broker that refuses the next client

Answers a client's CONNECT with return code 5 ("Not authorised"), to test how an application handles a refusal. Create the listener, point a client at Listener.Port, call its Connect, then call this.

uses
  System.SysUtils, Atlas.MqttCodec, Atlas.MqttTransport;

function RefuseNextClient(Listener: TAtlasTcpListener): Boolean;
var
  Peer: TAtlasTcpTransport;
  Parser: TAtlasMqttParser;
  Packet: TMqttPacket;
  Buffer: TBytes;
  Count: Integer;
begin
  Peer := Listener.Accept(5000);
  Result := Peer <> nil;
  if not Result then
    Exit;
  Parser := TAtlasMqttParser.Create;
  try
    SetLength(Buffer, 1024);
    repeat
      Count := Peer.Receive(Buffer, 3000);
      if Count <= 0 then
        Exit(False);
      Parser.Feed(Buffer, Count);
    until Parser.Next(Packet);
    Result := Packet.Kind = mkConnect;
    Packet := TMqttPacket.Create(mkConnAck);
    Packet.ReturnCode := 5;
    Peer.Send(TAtlasMqttCodec.Encode(Packet));
  finally
    Parser.Free;
    Peer.Free;
  end;
end;

TAtlasTcpTransport · TAtlasMqttBroker

Also in Atlas MQTT

TAtlasMqttClient · TAtlasMqttBroker

TAtlasTcpListener