nim-libp2p-experimental/examples/tutorial_1_connect.md

Hi all, welcome to the first article of the nim-libp2p's tutorial series!

This tutorial is for everyone who is interested in building peer-to-peer chatting applications. No Nim programming experience is needed.

To give you a quick overview, Nim is the programming language we are using and nim-libp2p is the Nim implementation of libp2p, a modular library that enables the development of peer-to-peer network applications.

Hope you'll find it helpful in your journey of learning. Happy coding! ;)

Before you start

The only prerequisite here is Nim, the programming language with a Python-like syntax and a performance similar to C. Detailed information can be found here.

Install Nim via their official website: https://nim-lang.org/install.html
Check Nim's installation via nim --version and its package manager Nimble via nimble --version.

You can now install the latest version of nim-libp2p:

nimble install libp2p@#master

A simple ping application

We'll start by creating a simple application, which is starting two libp2p switch, and pinging each other using the Ping protocol.

TIP: You can extract the code from this tutorial by running nim c -r tools/markdown_runner.nim examples/tutorial_1_connect.md in the libp2p folder!

Let's create a part1.nim, and import our dependencies:

import bearssl
import chronos

import libp2p
import libp2p/protocols/ping

bearssl is used as a cryptographic pseudorandom number generator
chronos the asynchronous framework used by nim-libp2p

Next, we'll create an helper procedure to create our switches. A switch needs a bit of configuration, and it will be easier to do this configuration only once:

proc createSwitch(ma: MultiAddress, rng: ref BrHmacDrbgContext): Switch =
  var switch = SwitchBuilder
    .new()
    .withRng(rng)       # Give the application RNG
    .withAddress(ma)    # Our local address(es)
    .withTcpTransport() # Use TCP as transport
    .withMplex()        # Use Mplex as muxer
    .withNoise()        # Use Noise as secure manager
    .build()

  return switch

This will create a switch using Mplex as a multiplexer, Noise to secure the communication, and TCP as an underlying transport.

You can of course tweak this, to use a different or multiple transport, or tweak the configuration of Mplex and Noise, but this is some sane defaults that we'll use going forward.

Let's now start to create our main procedure:

proc main() {.async, gcsafe.} =
  let
    rng = newRng()
    localAddress = MultiAddress.init("/ip4/0.0.0.0/tcp/0").tryGet()
    pingProtocol = Ping.new(rng=rng)

We created some variables that we'll need for the rest of the application: the global rng instance, our localAddress, and an instance of the Ping protocol.
The address is in the MultiAddress format. The port 0 means "take any port available".

tryGet is procedure which is part of the nim-result, that will throw an exception if the supplied MultiAddress is not valid.

We can now create our two switches:

  let
    switch1 = createSwitch(localAddress, rng)
    switch2 = createSwitch(localAddress, rng)
    
  switch1.mount(pingProtocol)

  await switch1.start()
  await switch2.start()

We've mounted the pingProtocol on our first switch. This means that the first switch will actually listen for any ping requests coming in, and handle them accordingly.

Now that we've started the nodes, they are listening for incoming peers.
We can find out which port was attributed, and the resulting local addresses, by using switch1.peerInfo.addrs.

We'll dial the first switch from the second one, by specifying it's Peer ID, it's MultiAddress and the Ping protocol codec:

  let conn = await switch2.dial(switch1.peerInfo.peerId, switch1.peerInfo.addrs, PingCodec)

We now have a Ping connection setup between the second and the first switch, we can use it to actually ping the node:

  # ping the other node and echo the ping duration
  echo "ping: ", await pingProtocol.ping(conn)

  # We must close the connection ourselves when we're done with it
  await conn.close()

And that's it! Just a little bit of cleanup: shutting down the switches, waiting for them to stop, and we'll call our main procedure:

  await allFutures(switch1.stop(), switch2.stop()) # close connections and shutdown all transports
  
waitFor(main())

You can now run this program using nim c -r part1.nim, and you should see the dialing sequence, ending with a ping output.

In the next tutorial, we'll look at how to create our own custom protocol.