docs: auto relay example (#795)

* chore: auto relay example

* chore: update examples to use process arguments

* chore: add test setup for node tests and test for auto-relay

* chore: apply suggestions from code review

* chore: do not use promise for multiaddrs event on example

examples/auto-relay/test.js

@@ -0,0 +1,94 @@
+'use strict'
+
+const path = require('path')
+const execa = require('execa')
+const pDefer = require('p-defer')
+const uint8ArrayToString = require('uint8arrays/to-string')
+
+function startProcess (name, args = []) {
+  return execa('node', [path.join(__dirname, name), ...args], {
+    cwd: path.resolve(__dirname),
+    all: true
+  })
+}
+
+async function test () {
+  let output1 = ''
+  let output2 = ''
+  let output3 = ''
+  let relayAddr
+  let autoRelayAddr
+
+  const proc1Ready = pDefer()
+  const proc2Ready = pDefer()
+
+  // Step 1 process
+  process.stdout.write('relay.js\n')
+
+  const proc1 = startProcess('relay.js')
+  proc1.all.on('data', async (data) => {
+    process.stdout.write(data)
+
+    output1 += uint8ArrayToString(data)
+
+    if (output1.includes('Listening on:') && output1.includes('/p2p/')) {
+      relayAddr = output1.trim().split('Listening on:\n')[1].split('\n')[0]
+      proc1Ready.resolve()
+    }
+  })
+
+  await proc1Ready.promise
+  process.stdout.write('==================================================================\n')
+
+  // Step 2 process
+  process.stdout.write('listener.js\n')
+
+  const proc2 = startProcess('listener.js', [relayAddr])
+  proc2.all.on('data', async (data) => {
+    process.stdout.write(data)
+
+    output2 += uint8ArrayToString(data)
+
+    if (output2.includes('Advertising with a relay address of') && output2.includes('/p2p/')) {
+      autoRelayAddr = output2.trim().split('Advertising with a relay address of ')[1]
+      proc2Ready.resolve()
+    }
+  })
+
+  await proc2Ready.promise
+  process.stdout.write('==================================================================\n')
+
+  // Step 3 process
+  process.stdout.write('dialer.js\n')
+
+  const proc3 = startProcess('dialer.js', [autoRelayAddr])
+  proc3.all.on('data', async (data) => {
+    process.stdout.write(data)
+
+    output3 += uint8ArrayToString(data)
+
+    if (output3.includes('Connected to the auto relay node via')) {
+      const remoteAddr = output3.trim().split('Connected to the auto relay node via ')[1]
+
+      if (remoteAddr === autoRelayAddr) {
+        proc3.kill()
+        proc2.kill()
+        proc1.kill()
+      } else {
+        throw new Error('dialer did not dial through the relay')
+      }
+    }
+  })
+
+  await Promise.all([
+    proc1,
+    proc2,
+    proc3
+  ]).catch((err) => {
+    if (err.signal !== 'SIGTERM') {
+      throw err
+    }
+  })
+}
+
+module.exports = test