Udp support

[shargon]

Also, i included the possibility of listen only on certain interfaces, not in all

• Close Extend VersionPayload with service information #548

[erikzhang]

We need to modify VersionPayload too.

[vncoelho]

@shargon,it looks interesting and more organized.
What are the next changes? For example, at RemoteNode?

[shargon]

Ok! maybe we should add some Attributes inside VersionProtocol in order to close #548 ?

[shargon]

check fe42fcd for the refactor of VersionPayload

[erikzhang]

When does a node actively send UDP messages? I didn't find it in the code.

[shargon]

Only it response for udp message, it never start sending

[erikzhang]

Only it response for udp message, it never start sending

But who send it first? If no one send UDP, the functions are not used.

[shargon]

If you want to send a tx to other node (by other client for example) you will receive and be able to response.

Is like Websocket, listen and response

[ThomasLobker]

I think there is a problem, the max package size of UDP is 65535. But a transaction or block can much larger then it.

Both UDP and TCP have a maximum packet size of (about) 64KiB. And the IP layer handles fragmentation anytime the packet is larger than the MTU, there is not really a difference here between UDP and TCP.

If we split the message when it is sent and combine it when it is accepted, then it is better to use TCP directly.

Yes absolutely 👍

Also keep in mind that any bidirectional traffic between a node and a client behind NAT would require things like NAT traversal with keep-alives. Trust me that this will be a huge pain in many scenario's.

For broadcasting unidirectional packets like transactions UDP can be great though and it will give you much better performance. Just sending your transaction to many nodes at once and stop caring about it. For anything else, don't mind UDP and just keep using TCP 😉

[erikzhang]

If you want to send transactions to other nodes, you'll need to send inv message first, right? Then you will receive getdata messages from these nodes asynchronously. How do you use UDP to broadcast?

[ThomasLobker]

If you want to send transactions to other nodes, you'll need to send inv message first, right?

How about the RPC sendrawtransaction method? With RPC over UDP you could send your raw transaction to 10 nodes at the same time for extra redundancy.

[shargon]

Udp messages could be received in wrong order, so we can't combine it. My first idea with udp is only for a listener, and a faster way of receive some messages, not all of them

[erikzhang]

I think it's difficult to use UDP MultiCast on Internet. Without MultiCast, what is the use of UDP for us?

[shargon]

I think it's difficult to use UDP MultiCast on Internet. Without MultiCast, what is the use of UDP for us?

Not to many :P

If you wish, i can remove all the udp functionality, and maintain the other changes.

[erikzhang]

Conflicts

[codecov-io]

Codecov Report

Merging #728 into master will decrease coverage by <.01%.
The diff coverage is 3.14%.

@@            Coverage Diff             @@
##           master     #728      +/-   ##
==========================================
- Coverage   38.39%   38.39%   -0.01%     
==========================================
  Files         176      178       +2     
  Lines       12465    12526      +61     
==========================================
+ Hits         4786     4809      +23     
- Misses       7679     7717      +38

Impacted Files	Coverage Δ
neo/Network/P2P/Capabilities/NodeCapability.cs	61.53% <ø> (ø)	⬆️
neo/Network/P2P/ChannelsConfig.cs	0% <0%> (ø)	⬆️
neo/Network/P2P/RemoteNode.cs	3.75% <0%> (-0.03%)	⬇️
neo/Network/RPC/RpcServer.cs	0% <0%> (ø)	⬆️
neo/Network/P2P/UdpRequest.cs	0% <0%> (ø)
neo/Network/P2P/TaskSession.cs	0% <0%> (ø)	⬆️
neo/Network/P2P/UdpResponse.cs	0% <0%> (ø)
neo/Network/P2P/ProtocolHandler.cs	12.22% <1.36%> (+5.25%)	⬆️
neo/Network/P2P/Capabilities/ServerCapability.cs	73.33% <100%> (ø)	⬆️
neo/Network/P2P/LocalNode.cs	16.93% <6.25%> (-1.42%)	⬇️
... and 5 more

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[ZhangTao1596]

I think we can treat it as a "connection" if two nodes exchange verison via udp.
So every node should have a struct to manage these connections in order to broadcast.

[shargon]

If we decide that this is not useful, we can close this pr