[PD-dev] netsend/netreceive UDP ignore ECONNREFUSED

Christof Ressi christof.ressi at gmx.at
Tue Mar 26 02:21:46 CET 2019

that's very strange as it shouldn't make any difference. what I *suspect* is really happening is that the socket isn't added to the readset in sys_domicrosleep and so the pollfunction (containing the call to recv) is never called. this is just a wild guess, though.

on the other hand, I couldn't test this quickly, as sending back to [netsend -u] seems to be broken anyway... I've tried with both providing the src port like [connect localhost 9999 9997( or getting the port number with [iemnet/udpreceive]. I even doesn't work when using another [netsend -u]...

actually, the easiest fix is to just suppress creating the right outlet (so no socketreceiver is created). it's a bit lazy, though :-) but it could mean something like: we just want to "broadcast" messages without any notion of "connection", therefore we don't need the right outlet either.

here's a prove of concept: https://github.com/Spacechild1/pure-data/tree/netsend-experiment

I've attached a patch to demonstrate the problem with sending to [netsend] and my lazy fix for [netsend].


Gesendet: Montag, 25. März 2019 um 23:03 Uhr
Von: "Dan Wilcox" <danomatika at gmail.com>
An: "Christof Ressi" <christof.ressi at gmx.at>
Cc: pd-dev <pd-dev at lists.iem.at>
Betreff: Re: [PD-dev] netsend/netreceive UDP ignore ECONNREFUSED

I did some quick hacking/testing and it seems that for UDP:
* not calling connect() in netsend_connect
* using sendto() with the server address struct in netsend_dosend
* & using recvfrom() instead of recv() in the socketreceiver
results in no "Connection refused" errors being thrown.


On Mar 25, 2019, at 11:32 AM, Christof Ressi <christof.ressi at gmx.at[mailto:christof.ressi at gmx.at]> wrote: 

> For connectionless sending essentially, I think we would need to forego the call to connect() in netsend_connect and keep a copy of the socket address struct
IIUC, 'connect' on a UDP sockket does exactly that: it doesn't really "connect" to anything but just stores the default destination address, so 'connect' + 'send' is equivalent to 'sendto'.
at least that's how it has always worked for me.

Gesendet: Montag, 25. März 2019 um 10:59 Uhr
Von: "Dan Wilcox" <danomatika at gmail.com[mailto:danomatika at gmail.com]>
An: "Chris McCormick" <chris at mccormick.cx[mailto:chris at mccormick.cx]>
Cc: pd-dev <pd-dev at lists.iem.at[mailto:pd-dev at lists.iem.at]>
Betreff: Re: [PD-dev] netsend/netreceive UDP ignore ECONNREFUSED

Sure, however neither netsend nor udpsend work this way, so I was first trying to see what I could do without changing the internals a whole lot. It's definitely not "connectionless" when it keeps returning to a receiver...
For connectionless sending essentially, I think we would need to forego the call to connect() in netsend_connect and keep a copy of the socket address struct to use with sendto() instead of send() when actually sending. Since sendto() takes the address directly, it doesn't need a connect() ahead of time. Also, the UDP netsend / netreceive relay behavior could then use sendto() and recvfrom().
So conceptually, the current behavior of calling connect() for both UDP and TCP needs to change and I'd think then the the "connected" outlet for UDP simply means the socket is set up, but has no connotation for a current "connection." Again, I'm not sure how that would affect patches which would rely on the old behavior...
On Mar 25, 2019, at 3:42 AM, Chris McCormick <chris at mccormick.cx[mailto:chris at mccormick.cx]> wrote: 

Hi Dan,

On 23/3/19 5:56 am, Dan Wilcox wrote:From my reading on the socket API, sending a UDP message conceptually shouldn't care about whether the receiver is there. However this is detected on a lower networking layer and propagated up to the application layer where it can be used or ignored.
You probably know this already but it is possible to operate UDP in connectionless or connection-oriented mode. Connection-oriented is somewhere between TCP and connectionless. In connection-oriented mode I suppose you would want to know if the other side is there or not, whereas with connectionless you probably just want to fire and forget. Not sure if this affects what you are doing but might help explain what you're seeing.




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Dan Wilcox
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