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Can I use IdUDPClient to send an M-SEARCH request?

There are several uPNP devices on my network. I am trying to send an M-SEARCH request to the network and hope to receive answers from it. This is what I am trying:

var sIP, sOut: string;
    iPort: Word;
    S: TStringBuilder;
begin
  S := TStringBuilder.Create;
  try
    S.Append('M-SEARCH * HTTP/1.1').AppendLine
     .Append('HOST: 239.255.255.250:1900').AppendLine
     .Append('MAN: "ssdp:discover"').AppendLine
     .Append('MX: 10').AppendLine
     .Append('ST: ssdp:all').AppendLine;

    IdUDPClient1.ReceiveTimeout := 3000;
    IdUDPClient1.Broadcast(S.ToString, 1900, '239.255.255.250');
    sOut := IdUDPClient1.ReceiveString(sIP, iPort);
    Memo1.Lines.Add(sIP);
    Memo1.Lines.Add(IntToStr(iPort));
    Memo1.Lines.Add(sOut);
  finally
    S.Free;
  end;
end;

I do not receive anything from the UDP client. I use Wireshark to monitor network traffic, and no message is sent from my host.

Any ideas? Thank.

I finally found the answer:

uses
  System.SysUtils, IdUDPClient, IdStack;

var S: TStringBuilder;
    U: TIdUDPClient;
    iPeerPort: Word;
    sPeerIP, sResponse: string;
begin
  U := TIdUDPClient.Create(nil);
  S := TStringBuilder.Create;
  try
    S.Append('M-SEARCH * HTTP/1.1').AppendLine
     .Append('HOST: 239.255.255.250:1900').AppendLine
     .Append('MAN: "ssdp:discover"').AppendLine
     .Append('MX: 3').AppendLine
     .Append('ST: ssdp:all').AppendLine
     .AppendLine;

    U.BoundIP := GStack.LocalAddress;
    U.Send('239.255.255.250', 1900, S.ToString);

    U.ReceiveTimeout := 1000;
    repeat
      sResponse := U.ReceiveString(sPeerIP, iPeerPort);
      if iPeerPort <> 0 then begin
        WriteLn(Format('%s:%d', [sPeerIP, iPeerPort]));
        WriteLn(sResponse);
      end;
    until iPeerPort = 0;
    ReadLn;
  finally
    S.Free;
    U.Free;
  end;
end.
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3 answers

Call AppendLine()twice at the end of the row builder. HTTP request headers end with two CRLF pairs, but you add only one pair, so you send an incomplete request.

+6
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Fast and dirty solution using TIdUDPServer (Indy 9).

TIdUDPServer Object Inspector Bindings IP, . 10.1.0.78:08, BroadcastEnabled Active true. TMemo TButton .

OnClick UDPRead :

uses IdSocketHandle;
...
procedure TForm1.Button1Click(Sender: TObject);
begin
  IdUDPServer1.Send('239.255.255.250', 1900, 'M-SEARCH * HTTP/1.1' + #13#10 +
     'HOST: 239.255.255.250:1900' + #13#10 +
     'MAN: "ssdp:discover"'+ #13#10 +
     'MX: 3'+ #13#10 +
     'ST: ssdp:all'+ #13#10 +
     #13#10);
end;

procedure TForm1.IdUDPServer1UDPRead(Sender: TObject; AData: TStream; ABinding: TIdSocketHandle);
var 
   data: string;
begin

   setlength(data, Adata.Size - AData.Position); //No fragmentation :)        
   AData.ReadBuffer(data[1], length(data));

   memo1.Lines.Add('Read: ' + inttostr(AData.Position) + ' / ' + inttostr(AData.Size) + ' PeerIP: ' + ABinding.PeerIP);       
   memo1.Lines.Add(data);
end;

, .

+3

For M-SEARCH multicast, the message format is defined below. Values ​​between * * are placeholders for actual values.

M-SEARCH * HTTP/1.1
HOST: 239.255.255.250:1900
MAN: "ssdp:discover"
MX: *seconds to delay response*
ST: *search target*
USER-AGENT: *OS/version UPnP/1.1 product/version*

So you need to fix ReceiveTimeout before

U.ReceiveTimeout := 3000;

It should be at least equal to the delay of your request (MX: 3) 3 seconds = 3000 milliseconds

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