Breaking Datagram API change.

[cheatfate]

DatagramCallback* = proc(transp: DatagramTransport,
                         remote: TransportAddress): Future[void] {.gcsafe.}
                         message: seq[byte],
                         remote: TransportAddress,
                         error: OSErrorCode): Future[void]

message - UDP message bytes.
If len(message) == 0 you need to check OSErrorCode to obtain error code.

[arnetheduck]

openArray[byte] tends to give more flexibility for the implementation.. a common option later on is to allow the original caller to set up a byte buffer of their choice..

[arnetheduck]

this is also the kind of place where Result is appropriate - giving either an error or a buffer but never both - makes for cleaner code everywhere

[cheatfate]

@arnetheduck we can't use openarray[T] because it can't be captured inside of iterator, so it can't work in async procedures.

[yglukhov]

Seems like error which can happen here is either not realistic or unrelated to remote-specific message receiving. Thus I would consider removing the error from this function signature. For remote-unrelated events I would introduce another callback like onNetworkChanged.

[cheatfate]

Sorry, but chronos is cross-platform framework, and if Linux has small number of errors, BSD/MacOS and Windows has much more, so i wish to leave error code here.