SOLVED UDP broadcast listener
lazarus / 38-Networking and Web Programming

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samsvl · 2018-11-17 16:30

I have an outside thermometer broadcasting temperature to my lan with
address 192.168.0.255, port 8088. I am trying to receive the data on
my win8.1 pc using a freepascal program below. It runs up till
writeln('fpbind ',k), writes zero, and then it seems to hang, while
the thermometer is broadcasting. Can anybody help me?

uses sockets;

var
   S: longint;
   SA: SockAddr;
   k: longint;
   buf: array[0..255] of char;
   L: ssize_t;
   len: Tsocklen;
   broadcast: integer;

begin
S := fpSocket(AF_INET,SOCK_DGRAM,0);
writeln('socket ',S);
SA.sin_family := AF_INET;
SA.sin_port := htons(8088);
SA.sin_addr.s_addr := htonl(INADDR_ANY); {StrToHostAddr('');  }
broadcast := 1;
k :=
fpsetsockopt(S,SOL_SOCKET,SO_BROADCAST,@broadcast,sizeof(broadcast));
writeln('fpsetsockopt ',k);
k := fpBind (S, @SA, sizeof(SA));
writeln('fpbind ',k);
len := sizeof(SA);
L := fprecvfrom(S,@buf[0],255,0,@SA,@len);
write('fprecvfrom ',L); readln;
write(SocketError); readln;
end.

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skalogryz · 2018-11-17 18:03

Make sure you’re not blocked by the firewall

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samsvl · 2018-11-17 20:24

Thanks for your reaction. But all is within my lan, so I don't expect
firewall problems. Moreover, a simple python implementation on my
Raspberry Pi does work.

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engkin · 2018-11-18 00:54

Quote from: samsvl on November 17, 2018, 05:30:22 pmI have an outside
thermometer
Just curious, which thermometer are you using?

Quote from: samsvl on November 17, 2018, 05:30:22 pmbroadcasting
temperature to my lan with address 192.168.0.255, port 8088.instead of
192.168.0.255, try 255.255.255.255

Quote from: samsvl on November 17, 2018, 05:30:22 pm I am trying to
receive the data on my win8.1 pc using a freepascal program
below.Which FreePascal version? 32 or 64-bit?
Is your win8.1 64-bit?

Quote from: samsvl on November 17, 2018, 05:30:22 pmIt runs up till
writeln('fpbind ',k), writes zero, and then it seems to hang, while
the thermometer is broadcasting.This sounds to me like it's waiting to
receive data:
QuoteIf no incoming data is available at the socket, the recvfrom
function blocks and waits for data to arrive according to the blocking
rules defined for WSARecv
Quote from: samsvl on November 17, 2018, 05:30:22 pmCan anybody help
me?What is your network setup?
I assume you already used something like WireShark to make sure your
computer is receiving the broadcasted temperature?

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samsvl · 2018-11-18 12:34

Quote from: engkin on November 18, 2018, 01:54:58 amQuote from: samsvl
on November 17, 2018, 05:30:22 pmI have an outside thermometer
Just curious, which thermometer are you using?
Homebrew: an RTD connected to the ADC of an ATtiny45 microcontroller
which transfers the data via SPI to an ENC28J60 SPI to ethernet
converter, connected to my LAN
Quote from: samsvl on November 17, 2018, 05:30:22 pmbroadcasting
temperature to my lan with address 192.168.0.255, port 8088.instead of
192.168.0.255, try 255.255.255.255
I'll implement your suggestion, will take some time because the
address is hard coded in the ATtiny program
Quote from: samsvl on November 17, 2018, 05:30:22 pm I am trying to
receive the data on my win8.1 pc using a freepascal program
below.Which FreePascal version? 32 or 64-bit?
3.0.2 32 bit
Is your win8.1 64-bit?
yes

Quote from: samsvl on November 17, 2018, 05:30:22 pmIt runs up till
writeln('fpbind ',k), writes zero, and then it seems to hang, while
the thermometer is broadcasting.This sounds to me like it's waiting to
receive data:
QuoteIf no incoming data is available at the socket, the recvfrom
function blocks and waits for data to arrive according to the blocking
rules defined for WSARecvYes, that's what I think also. But why?

Quote from: samsvl on November 17, 2018, 05:30:22 pmCan anybody help
me?What is your network setup?
I assume you already used something like WireShark to make sure your
computer is receiving the broadcasted temperature?
Yes, Wireshark shows the broadcast message, but since there is no
client-server communication I can't see if my PC accepts the message.

I just installed the script on my Raspberry PI A connencted to the
same LAN, and there it runs without problems. So the issue must be
windows related.

Again, thanks for your reaction,

Sam

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Bram71 · 2018-11-18 14:01

Can it be the windows firewall blocking the traffic? Just disable it
for a moment to check...

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lucamar · 2018-11-18 14:29

Also, while you're (re-)checking the firewall make double-sure that
both the IP address and the port are available for UDP to your
application. I had a problem like this once and it was because the
firewall was blocking the port.

Good luck!

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samsvl · 2018-11-18 19:27

You all pointed to the firewall, and you all were right !!!
Thanks a lot, problem solved.