docs(example): add pubssub message filter example

moved the filter folder

rename folder

docs(refactor): clean up pubsub validator example

examples/pubsub/message-filtering/1.js

@@ -0,0 +1,82 @@
+/* eslint-disable no-console */
+'use strict'
+
+const { Buffer } = require('buffer')
+const Libp2p = require('../../../')
+const TCP = require('libp2p-tcp')
+const Mplex = require('libp2p-mplex')
+const { NOISE } = require('libp2p-noise')
+const SECIO = require('libp2p-secio')
+const Gossipsub = require('libp2p-gossipsub')
+
+const createNode = async () => {
+  const node = await Libp2p.create({
+    addresses: {
+      listen: ['/ip4/0.0.0.0/tcp/0']
+    },
+    modules: {
+      transport: [TCP],
+      streamMuxer: [Mplex],
+      connEncryption: [NOISE, SECIO],
+      pubsub: Gossipsub
+    }
+  })
+
+  await node.start()
+  return node
+}
+
+(async () => {
+  const topic = 'fruit'
+
+  const [node1, node2, node3] = await Promise.all([
+    createNode(),
+    createNode(),
+    createNode(),
+  ])
+
+  // node1 conect to node2 and node2 conect to node3
+  node1.peerStore.addressBook.set(node2.peerId, node2.multiaddrs)
+  await node1.dial(node2.peerId)
+
+  node2.peerStore.addressBook.set(node3.peerId, node3.multiaddrs)
+  await node2.dial(node3.peerId)
+
+  //subscribe
+  await node1.pubsub.subscribe(topic, (msg) => {
+    console.log(`node1 received: ${msg.data.toString()}`)
+  })
+
+  await node2.pubsub.subscribe(topic, (msg) => {
+    console.log(`node2 received: ${msg.data.toString()}`)
+  })
+
+  await node3.pubsub.subscribe(topic, (msg) => {
+    console.log(`node3 received: ${msg.data.toString()}`)
+  })
+
+  const validateFruit = (msgTopic, peer, msg) => {
+    const fruit = msg.data.toString();
+    const validFruit = ['banana', 'apple', 'orange']
+    const valid = validFruit.includes(fruit);
+    return valid;
+  }
+
+  //validate fruit
+  node1.pubsub._pubsub.topicValidators.set(topic, validateFruit);
+  node2.pubsub._pubsub.topicValidators.set(topic, validateFruit);
+  node3.pubsub._pubsub.topicValidators.set(topic, validateFruit);
+
+  // node1 publishes "fruits" every five seconds
+  var count = 0;
+  const myFruits = ['banana', 'apple', 'car', 'orange'];
+  // car is not a fruit !
+  setInterval(() => {
+    console.log('############## fruit ' + myFruits[count] + ' ##############')
+    node1.pubsub.publish(topic, Buffer.from(myFruits[count]))
+    count++
+    if (count == myFruits.length) {
+      count = 0
+    }
+  }, 5000)
+})()

examples/pubsub/message-filtering/README.md

@@ -0,0 +1,108 @@
+# Filter Messages
+
+To prevent undesired data from being propagated on the network, we can apply a filter to Gossipsub. Messages that fail validation in the filter will not be re-shared.
+
+## 1. Setting up a PubSub network with three nodes
+
+First, let's update our libp2p configuration with a pubsub implementation.
+
+```JavaScript
+const Libp2p = require('libp2p')
+const Gossipsub = require('libp2p-gossipsub')
+
+const node = await Libp2p.create({
+  addresses: {
+    listen: ['/ip4/0.0.0.0/tcp/0']
+  },
+  modules: {
+    transport: [ TCP ],
+    streamMuxer: [ Mplex ],
+    connEncryption: [ NOISE, SECIO ],
+    pubsub: Gossipsub
+  }
+})
+```
+
+Then, create three nodes and connect them together. In this example, we will connect the nodes in series. Node 1 connected with node 2 and node 2 connected with node 3.
+
+```JavaScript
+const [node1, node2, node3] = await Promise.all([
+  createNode(),
+  createNode(),
+  createNode(),
+])
+
+node1.peerStore.addressBook.set(node2.peerId, node2.multiaddrs)
+await node1.dial(node2.peerId)
+
+node2.peerStore.addressBook.set(node3.peerId, node3.multiaddrs)
+await node2.dial(node3.peerId)
+```
+
+Now we' can subscribe to the fruit topic and log incoming messages.
+
+```JavaScript
+const topic = 'fruit'
+
+await node1.pubsub.subscribe(topic, (msg) => {
+  console.log(`node1 received: ${msg.data.toString()}`)
+})
+
+await node2.pubsub.subscribe(topic, (msg) => {
+  console.log(`node2 received: ${msg.data.toString()}`)
+})
+
+await node3.pubsub.subscribe(topic, (msg) => {
+  console.log(`node3 received: ${msg.data.toString()}`)
+})
+```
+Finally, let's define the additional filter in the fruit topic.
+
+```JavaScript
+const validateFruit = (msgTopic, peer, msg) => {
+  const fruit = msg.data.toString();
+  const validFruit = ['banana', 'apple', 'orange']
+  const valid = validFruit.includes(fruit);
+  return valid;
+}
+
+node1.pubsub._pubsub.topicValidators.set(topic, validateFruit);
+node2.pubsub._pubsub.topicValidators.set(topic, validateFruit);
+node3.pubsub._pubsub.topicValidators.set(topic, validateFruit);
+```
+
+In this example, node one has an outdated version of the system, or is a malicious node. When it tries to publish fruit, the messages are re-shared and all the nodes share the message. However, when it tries to publish a vehicle the message is not re-shared.
+
+```JavaScript
+var count = 0;
+const myFruits = ['banana', 'apple', 'car', 'orange'];
+
+setInterval(() => {
+  console.log('############## fruit ' + myFruits[count] + ' ##############')
+  node1.pubsub.publish(topic, Buffer.from(myFruits[count]))
+  count++
+  if (count == myFruits.length) {
+    count = 0
+  }
+}, 5000)
+```
+
+Result
+
+```
+> node 1.js
+############## fruit banana ##############
+node1 received: banana
+node2 received: banana
+node3 received: banana
+############## fruit apple ##############
+node1 received: apple
+node2 received: apple
+node3 received: apple
+############## fruit car ##############
+node1 received: car
+############## fruit orange ##############
+node1 received: orange
+node2 received: orange
+node3 received: orange
+```