Netty - reliable UDP connection for Nim.

nimble install netty

API reference

About

Netty is a reliable connection over UDP aimed at games. Normally UDP packets can get duplicated, dropped, or come out of order. Netty makes sure packets are not duplicated, re-sends them if they get dropped, and all packets come in order. UDP packets might also get split if they are above 512 bytes and also can fail to be sent if they are bigger than 1-2k. Netty breaks up big packets and sends them in pieces making sure each piece comes reliably in order. Finally sometimes it is impossible for two clients to communicate directly with TCP because of NATs, but Netty can send hole punch probes to help them connect.

Documentation

API reference: https://treeform.github.io/netty

Is Netty an implementation of TCP?

TCP is really bad for short latency sensitive messages. TCP was designed for throughput (downloading files) not latency (games). Netty will resend stuff faster than TCP, Netty will not buffer and you also get NAT punch-through probes (which TCP does not have). Netty is basically "like TCP but for games". You should not be using Netty if you will be sending large amounts of data. By default Netty is capped at 250KB of data in flight (reactor.maxInFlight, configurable).

Features:

feature	TCP	UDP	Netty
designed for low latency	no	yes	yes
designed for throughput	yes	no	no
packet framing	no	yes	yes
packet ordering	yes	no	yes
packet splitting	yes	no	yes
packet retry	yes	no	yes
packet deduplication	yes	no	yes
hole punch through	no	yes	yes
connection handling	yes	no	yes
congestion control	yes	no	no
fixed in-flight byte cap	no	no	yes

Echo Server/Client example

server.nim

import netty
# listen for a connection on localhost port 1999var server =newReactor("127.0.0.1", 1999)
echo"Listening for UDP on 127.0.0.1:1999"# main loopwhiletrue:
# must call tick to both read and write
server.tick()
# usually there are no new messages, but if there arefor msg in server.messages:
# print message dataecho"GOT MESSAGE: ", msg.data
# echo message back to the client
server.send(msg.conn, "you said:"& msg.data)

client.nim

import netty
# create connectionvar client =newReactor()
# connect to servervar c2s = client.connect("127.0.0.1", 1999)
# send message on the connection
client.send(c2s, "hi")
# main loopwhiletrue:
# must call tick to both read and write
client.tick()
# usually there are no new messages, but if there arefor msg in client.messages:
# print message dataecho"GOT MESSAGE: ", msg.data

Chat Server/Client example

chatserver.nim

import netty
var server =newReactor("127.0.0.1", 2001)
echo"Listening for UDP on 127.0.0.1:2001"whiletrue:
server.tick()
for connection in server.newConnections:
echo"[new] ", connection.address
for connection in server.deadConnections:
echo"[dead] ", connection.address
for msg in server.messages:
echo"[msg]", msg.data
# send msg data to all connectionsfor connection in server.connections:
server.send(connection, msg.data)

chatclient.nim

import netty
var client =newReactor()
var connection = client.connect("127.0.0.1", 2001)
# get persons nameecho"what is your name?"var name =readLine(stdin)
echo"note: press enter to see if people sent you things"whiletrue:
client.tick()
for msg in client.messages:
echo msg.data
# wait for user to type a linelet line =readLine(stdin)
if line.len >0:
client.send(connection, name &":"& line)