libp2p doesn't make assumptions for you, instead, it enables you as the developer of the application to pick the modules you need to run your application, which can vary depending on the runtime you are executing. A libp2p node can use one or more Transports to dial and listen for Connections. These transports are modules that offer a clean interface for dialing and listening, defined by the interface-transport specification. Some examples of possible transports are: TCP, UTP, WebRTC, QUIC, HTTP, Pigeon and so on.

A more complete definition of what is a transport can be found on the interface-transport specification. A way to recognize a candidate transport is through the badge:

1. Creating a libp2p Bundle with TCP

When using libp2p, you always want to create your own libp2p Bundle, that is, pick your set of modules and create your network stack with the properties you need. In this example, we will create a bundle with TCP. You can find the complete solution on the file 1.js.

You will need 4 deps total, so go ahead and install all of them with:

> npm install libp2p libp2p-tcp peer-info async

Then, on your favorite text editor create a file with the .js extension. I've called mine 1.js.

First thing is to create our own bundle! Insert:

'use strict'

const libp2p = require('libp2p')
const TCP = require('libp2p-tcp')
const PeerInfo = require('peer-info')
const waterfall = require('async/waterfall')

// This MyBundle class is your libp2p bundle packed with TCP
class MyBundle extends libp2p {
  constructor (peerInfo) {
    // modules is a JS object that will describe the components
    // we want for our libp2p bundle
    const modules = {
      transport: [new TCP()]
    }
    super(modules, peerInfo)
  }
}

Now that we have our own MyBundle class that extends libp2p, let's create a node with it. We will use async/waterfall just for code structure, but you don't need to. Append to the same file:

let node

waterfall([
  // First we create a PeerInfo object, which will pack the
  // info about our peer. Creating a PeerInfo is an async
  // operation because we use the WebCrypto API
  // (yeei Universal JS)
  (cb) => PeerInfo.create(cb),
  (peerInfo, cb) => {
    // To signall the addresses we want to be available, we use
    // the multiaddr format, a self describable address
    peerInfo.multiaddrs.add('/ip4/0.0.0.0/tcp/0')
    // Now we can create a node with that PeerInfo object
    node = new MyBundle(peerInfo)
    // Last, we start the node!
    node.start(cb)
  }
], (err) => {
  if (err) { throw err }

  // At this point the node has started
  console.log('node has started (true/false):', node.isOn())
  // And we can print the now listening addresses.
  // If you are familiar with TCP, you might have noticed
  // that we specified the node to listen in 0.0.0.0 and port
  // 0, which means "listen in any network interface and pick
  // a port for me
  console.log('listening on:')
  node.peerInfo.multiaddrs.forEach((ma) => console.log(ma.toString()))
})

Running this should result in somehting like:

> node 1.js
node has started (true/false): true
listening on:
/ip4/127.0.0.1/tcp/61329/ipfs/QmW2cKTakTYqbQkUzBTEGXgWYFj1YEPeUndE1YWs6CBzDQ
/ip4/192.168.2.156/tcp/61329/ipfs/QmW2cKTakTYqbQkUzBTEGXgWYFj1YEPeUndE1YWs6CBzDQ

That QmW2cKTakTYqbQkUzBTEGXgWYFj1YEPeUndE1YWs6CBzDQ is the PeerId that was created during the PeerInfo generation.

2. Dialing from one node to another node

Now that we have our bundle, let's create two nodes and make them dial to each other! You can find the complete solution at 2.js.

For this step, we will need one more dependency.

> npm install pull-stream

We are going to reuse the MyBundle class from step 1, but this time to make things simpler, we will create two functions, one to create nodes and another to print the addrs to avoid duplicating code.

function createNode (callback) {
  let node

  waterfall([
    (cb) => PeerInfo.create(cb),
    (peerInfo, cb) => {
      peerInfo.multiaddrs.add('/ip4/0.0.0.0/tcp/0')
      node = new MyBundle(peerInfo)
      node.start(cb)
    }
  ], (err) => callback(err, node))
}

function printAddrs (node, number) {
  console.log('node %s is listening on:', number)
  node.peerInfo.multiaddrs.forEach((ma) => console.log(ma.toString()))
}

Now we are going to use async/parallel to create two nodes, print their addresses and dial from one node to the other.

parallel([
  (cb) => createNode(cb),
  (cb) => createNode(cb)
], (err, nodes) => {
  if (err) { throw err }

  const node1 = nodes[0]
  const node2 = nodes[1]

  printAddrs(node1, '1')
  printAddrs(node2, '2')

  node2.handle('/print', (protocol, conn) => {
    pull(
      conn,
      pull.map((v) => v.toString()),
      pull.log()
    )
  })

  node1.dial(node2.peerInfo, '/print', (err, conn) => {
    if (err) { throw err }

    pull(pull.values(['Hello', ' ', 'p2p', ' ', 'world', '!']), conn)
  })
})

The result should be look like:

> node 2.js
node 1 is listening on:
/ip4/127.0.0.1/tcp/62279/ipfs/QmeM4wNWv1uci7UJjUXZYfvcy9uqAbw7G9icuxdqy88Mj9
/ip4/192.168.2.156/tcp/62279/ipfs/QmeM4wNWv1uci7UJjUXZYfvcy9uqAbw7G9icuxdqy88Mj9
node 2 is listening on:
/ip4/127.0.0.1/tcp/62278/ipfs/QmWp58xJgzbouNJcyiNNTpZuqQCJU8jf6ixc7TZT9xEZhV
/ip4/192.168.2.156/tcp/62278/ipfs/QmWp58xJgzbouNJcyiNNTpZuqQCJU8jf6ixc7TZT9xEZhV
Hello p2p world!

3. Using multiple transports

Next, we want to be available in multiple transports to increase our chances of having common transports in the network. A simple scenario, a node running in the browser only has access to HTTP, WebSockets and WebRTC since the browser doesn't let you open any other kind of transport, for this node to dial to some other node, that other node needs to share a common transport.

What we are going to do in this step is to create 3 nodes, one with TCP, another with TCP+WebSockets and another one with just WebSockets. The full solution can be found on 3.js

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4. How to create a new libp2p transport

interface-transport
follow the interface
show other examples (webrtc, utp, udt (wip), etc)