Re: [Pharo-users] Issue with UDP Sockets

May 18, 2015


      Thanks for the explanation.

Best,
Manfred


On Mon, May 18, 2015 at 12:49 PM, Sven Van Caekenberghe <sven@stfx.eu>
wrote:
...
...
On 18 May 2015, at 12:44, Manfred KrÃ¶hnert <mkroehnert42@googlemail.com>
wrote:
Hello Sven,
thanks for your fast reply.
On Mon, May 18, 2015 at 11:41 AM, Sven Van Caekenberghe <sven@stfx.eu>
wrote:
Hi Manfred,
Did you see/study the example/test UDPSocketEchoTest ?
unfortunately I did not see this class, yet.
But I did look at the Socket class itself and Socket>>timeTestUDP (in
Pharo3).
We removed #timeTestUDP in Pharo 4 and higher, I believe, and replaced it
with proper tests/examples.
...
Also, UDP is very primitive: it is send and forget, returns no errors,
and is totally asynchronous. Listening should best be done in a separate
process.
Yes, UDP is primitive but the SSDP specification requires using UDP.
Here is how I would write your send part:
| message udpSocket |
  message := String crlf join: #(
   'M-SEARCH * HTTP/1.1'
   'HOST:239.255.255.250:1900'
   'MAN:"ssdp:discover'
   'ST:ssdp:all'
   'MX:1'
   '').
udpSocket := Socket newUDP.
  udpSocket sendData: message toHost: #[239 255 255 250] port: 1900.
  udpSocket waitForSendDoneFor: 5.
  udpSocket closeAndDestroy.
Thanks for this snippet.
For some reasons I do not understand yet, this gives me the expected
result in contrast to my own version.
I modified it like this to print the results on the Transcript:
| message udpSocket |
  message := String crlf join: #(
   'M-SEARCH * HTTP/1.1'
   'HOST:239.255.255.250:1900'
   'MAN:"ssdp:discover"'
   'ST:ssdp:all'
   'MX:1'
   '').
udpSocket := Socket newUDP.
  udpSocket sendData: message toHost: #[239 255 255 250] port: 1900.
  udpSocket waitForSendDoneFor: 5.
  udpSocket waitForData.
  [udpSocket dataAvailable ] whileTrue: [ | buffer |
    buffer := ByteArray new: 1024.
    udpSocket receiveUDPDataInto: buffer.
    Transcript show: 'Received: ', buffer.
    [udpSocket waitForDataFor: 1] on: Error do: [  ].
  ].
  udpSocket closeAndDestroy.
Currently, this will work for me, since I am not interested in
continuously detecting new devices.
But you mentioned reading should in general be done in a separate
process.
Would you reuse the existing udpSocket instance in this case or create a
separate one for reading?
I think if it is only for a one time use, it is OK like you are doing it.
...
Maybe nothing came back because the line ends where wrong ?
The lineendings I used are required by the SSDP specification.
I meant that writing '\r\n' has no effect in Pharo, this is not processed
(you could do this manually, of course). This is why I did it with the
#join:
That is the difference and why it works now, I guess.
...
HTH,
Sven
Thanks,
Manfred
...
On 18 May 2015, at 11:29, Manfred KrÃ¶hnert <
mkroehnert42@googlemail.com> wrote:
Hello everyone,
I am currently trying to get a list of UPnP device via SSDP (Simple
Service Discovery Protocol).
A minimalistic working NodeJS example looks like this:
var dgram = require('dgram');
    var message = new Buffer(
        "M-SEARCH * HTTP/1.1\r\n" +
        "HOST:239.255.255.250:1900\r\n" +
        "MAN:\"ssdp:discover\"\r\n" +
        "ST:ssdp:all\r\n" +
        "MX:1\r\n" +
        "\r\n"
    );
var client = dgram.createSocket("udp4");
client.on("message", function (msg, rinfo) {
        console.log("server got: " + msg + " from " + rinfo.address +
":" + rinfo.port);
    });
    client.send(message, 0, message.length, 1900, "239.255.255.250");
    client.close();
I tried to recreate the same functionality in Pharo with the following
piece of code:
| message udpSocket host |
  message := 'M-SEARCH * HTTP/1.1\r\n' ,
    'HOST:239.255.255.250:1900\r\n' ,
    'MAN:"ssdp:discover"\r\n' ,
    'ST:ssdp:all\r\n' ,
    'MX:1\r\n' , '\r\n'.
udpSocket := Socket newUDP.
  host :=  (NetNameResolver addressFromString: '239.255.255.250').
  udpSocket sendData: message toHost: host port: 1900.
  "udpSocket waitForData."
  Transcript show: 'Received: ' , udpSocket receiveData.
  udpSocket closeAndDestroy.
Unfortunately, this script hangs both in Pharo3 and Pharo4 (OS X
10.10, Pharo 30856 and 40611).
When I interrupt with Cmd+. the debugger shows the method
    Socket>>waitForDataIfClosed:
and the hang is apparently in the line
    self readSemaphore wait
Could anyone give me some advice if I should to do this differently or
what the issue with the Pharo script is?
Thanks in advance,
Manfred