code refactor & sync bugfixes

src/lansync-discovery.js

@@ -0,0 +1,135 @@
+'use strict'
+
+// UDP discovery for the LAN sync: every running PLWL beacons on the local
+// network and listens for the same beacon, so the devices list fills itself.
+// The beacon doubles as a liveness signal - a device drops off the list a few
+// seconds after its PLWL is closed.
+
+const dgram = require('dgram')
+const os = require('os')
+
+// Broadcast to the global address AND to every interface's own subnet
+// broadcast - some networks drop one or the other.
+function broadcastAddresses() {
+  const out = ['255.255.255.255']
+  const interfaces = os.networkInterfaces()
+  for (const list of Object.values(interfaces)) {
+    for (const iface of list || []) {
+      if (iface.family !== 'IPv4' || iface.internal || !iface.netmask) continue
+      const addr = ipToInt(iface.address)
+      const mask = ipToInt(iface.netmask)
+      if (addr == null || mask == null) continue
+      out.push(intToIp((addr | (~mask >>> 0)) >>> 0))
+    }
+  }
+  return out
+}
+
+function ipToInt(ip) {
+  const parts = String(ip).split('.')
+  if (parts.length !== 4) return null
+  let out = 0
+  for (const part of parts) {
+    const n = Number(part)
+    if (!Number.isInteger(n) || n < 0 || n > 255) return null
+    out = (out << 8) | n
+  }
+  return out >>> 0
+}
+
+function intToIp(int) {
+  return [24, 16, 8, 0].map(shift => (int >>> shift) & 255).join('.')
+}
+
+function createDiscovery({ identity, tag, protocol, port, beaconMs, deviceTtlMs, getPort }) {
+  let socket = null
+  let timer = null
+  let devicesCb = null
+  // id -> { id, name, address, port, at }
+  const seen = new Map()
+
+  function listDevices() {
+    const known = identity().known
+    const now = Date.now()
+    return [...seen.values()]
+      .filter(d => now - d.at <= deviceTtlMs)
+      .map(d => {
+        const pair = known[d.id]
+        return { id: d.id, name: d.name, address: d.address, port: d.port, paired: !!pair, code: pair ? pair.code : '' }
+      })
+      .sort((a, b) => String(a.name).localeCompare(String(b.name)))
+  }
+
+  function emitDevices() {
+    if (devicesCb) devicesCb(listDevices())
+  }
+
+  function pruneDevices() {
+    const now = Date.now()
+    let changed = false
+    for (const [id, device] of seen) {
+      if (now - device.at > deviceTtlMs) {
+        seen.delete(id)
+        changed = true
+      }
+    }
+    if (changed) emitDevices()
+  }
+
+  function beacon() {
+    if (!socket || !getPort()) return
+    const me = identity()
+    const payload = Buffer.from(JSON.stringify({ t: tag, v: protocol, id: me.deviceId, name: os.hostname(), port: getPort() }))
+    for (const address of broadcastAddresses()) {
+      try {
+        socket.send(payload, 0, payload.length, port, address)
+      } catch {}
+    }
+    pruneDevices()
+  }
+
+  function start(onDevices) {
+    stop()
+    devicesCb = onDevices
+    socket = dgram.createSocket({ type: 'udp4', reuseAddr: true })
+    socket.on('error', () => stop())
+    socket.on('message', (buf, rinfo) => {
+      let msg = null
+      try {
+        msg = JSON.parse(buf.toString('utf8'))
+      } catch {}
+      if (!msg || msg.t !== tag || msg.v !== protocol || !msg.id) return
+      if (msg.id === identity().deviceId) return // our own broadcast
+      const previous = seen.get(msg.id)
+      const next = { id: msg.id, name: String(msg.name || rinfo.address), address: rinfo.address, port: Number(msg.port) || 0, at: Date.now() }
+      const changed = !previous || previous.address !== next.address || previous.port !== next.port || previous.name !== next.name
+      seen.set(msg.id, next)
+      if (changed) emitDevices()
+    })
+    socket.bind(port, () => {
+      try {
+        socket.setBroadcast(true)
+      } catch {}
+      beacon()
+      timer = setInterval(beacon, beaconMs)
+    })
+  }
+
+  function stop() {
+    if (timer) {
+      clearInterval(timer)
+      timer = null
+    }
+    if (socket) {
+      const closing = socket
+      socket = null
+      try {
+        closing.close()
+      } catch {}
+    }
+  }
+
+  return { start, stop, listDevices }
+}
+
+module.exports = { createDiscovery }