[PD] receive UDP message from 224.0.0.1

[Christof Ressi]

Hmmm... 57120 happens to be the default port of sclang (the 
SuperCollider language interpreter). Could it be that sclang(.exe) is 
running? Check the task manager to be sure.

Explanation: Generally, only one application can listen to a port at a 
time. Normally, applications will just refuse to bind to ports that are 
already taken. However, Pd sets the SO_REUSEADDR socket option, which 
allows to bind to an existing port.

This is needed for TCP sockets, because they typically "linger" for a 
while after you close them. If you close and immediately reopen a patch, 
[netreceive] would refuse to bind.

However, we probably should /not/ set SO_REUSEADDR for UDP sockets 
because it doesn't do anything useful. On the contrary, it just causes 
confusion because [netreceive -u] does not post an error if the port is 
already taken.

Christof

On 10.01.2024 23:08, João Pais wrote:
> Hi everyone,
>
> I'm trying to receive some UDP data from a mobile device into Pd. The 
> data arrives in the computer (windows or ubuntu), here is a 
> description from wireshark:
>
> Frame 173: 90 bytes on wire (720 bits), 90 bytes captured (720 bits) 
> on interface \Device\NPF_{2ADD2685-ACB9-4C51-B708-F1F62FAE86C7}, id 0
> Ethernet II, Src: XiaomiCommun_1d:0e:fd (4c:e0:db:1d:0e:fd), Dst: 
> IPv4mcast_01 (01:00:5e:00:00:01)
> Internet Protocol Version 4, Src: 192.168.178.34, Dst: 224.0.0.1
> User Datagram Protocol, Src Port: 43641, Dst Port: 57120
> Data (48 bytes)
>
>
> But with [netreceive -u -b 57120] (or any other options to netreceive) 
> no data comes into Pd. Does anyone have any suggestion on how to 
> receive the data?
>
> When is sent to 224.0.0.1, the data gets into the computer but not 
> into Pd. But if other udp data is sent to the broadcast ip 
> (192.168.178.255) from the same device, it does get also into Pd.
>
> Frame 31: 66 bytes on wire (528 bits), 66 bytes captured (528 bits) on 
> interface \Device\NPF_{2ADD2685-ACB9-4C51-B708-F1F62FAE86C7}, id 0
> Ethernet II, Src: XiaomiCommun_1d:0e:fd (4c:e0:db:1d:0e:fd), Dst: 
> Broadcast (ff:ff:ff:ff:ff:ff)
> Internet Protocol Version 4, Src: 192.168.178.34, Dst: 192.168.178.255
> User Datagram Protocol, Src Port: 42797, Dst Port: 57120
> Data (24 bytes)
>
> Best,
>
> Joao
>
>
>
>
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