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bare-mdns-discovery

bare-mdns-discovery

stable

bare-mdns-discovery — bare-mdns-discovery.

npm i bare-mdns-discovery

Usage

Low-level mDNS queries

const { MDNS } = require('bare-mdns-discovery')

const mdns = new MDNS({ debug: true })
await mdns.ready()

mdns.on('records', (records, rinfo) => {
  console.log('from:', rinfo.address)
  for (const r of records) {
    console.log(r.type, r.name, r.data)
  }
})

mdns.query('_services._dns-sd._udp.local')
mdns.query('_http._tcp.local')
mdns.query('_googlecast._tcp.local')

setTimeout(() => mdns.close(), 10000)

Service discovery

const { Discovery } = require('bare-mdns-discovery')

const discovery = new Discovery({ service: 'googlecast' })
await discovery.ready()

discovery.on('service', (service) => {
  console.log('Found:', service.name, service.address, service.port)
})

const services = await discovery.discover(10) // 10 second timeout
console.log('All services:', services)

await discovery.close()

Extending for specific services

const { Discovery } = require('bare-mdns-discovery')

class MyServiceDiscovery extends Discovery {
  constructor(opts = {}) {
    super({ ...opts, service: 'myservice' })
  }

  _parseService(records, rinfo) {
    const service = super._parseService(records, rinfo)
    if (!service) return null

    // Add custom filtering or fields
    return {
      ...service,
      customField: service.txt.someKey
    }
  }
}

API

MDNS

new MDNS(opts?: MDNSOptions)

Send and receive raw mDNS queries and records over UDP multicast. Extends ReadyResource; open it with ready() and release its socket with close().

Parameters

ParameterTypeDefaultDescription
opts?MDNSOptions—Options; see MDNSOptions.

debug: boolean

Whether internal activity is logged to the console.

emit(event: 'records', records: Record[], rinfo: RecordInfo): boolean

Overloads:

emit(event: 'records', records: Record[], rinfo: RecordInfo): boolean
emit(event: 'error', err: Error): boolean
emit(event: 'ready'): boolean
emit(event: 'close'): boolean

Parameters

ParameterTypeDefaultDescription
event'records'——
recordsRecord[]——
rinfoRecordInfo——

off(event: 'records', listener: (records: Record[], rinfo: RecordInfo) => void): this

Overloads:

off(event: 'records', listener: (records: Record[], rinfo: RecordInfo) => void): this
off(event: 'error', listener: (err: Error) => void): this
off(event: 'ready', listener: () => void): this
off(event: 'close', listener: () => void): this

Parameters

ParameterTypeDefaultDescription
event'records'——
listener(records: Record[], rinfo: RecordInfo) => void——

on(event: 'records', listener: (records: Record[], rinfo: RecordInfo) => void): this

Overloads:

on(event: 'records', listener: (records: Record[], rinfo: RecordInfo) => void): this
on(event: 'error', listener: (err: Error) => void): this
on(event: 'ready', listener: () => void): this
on(event: 'close', listener: () => void): this

Parameters

ParameterTypeDefaultDescription
event'records'——
listener(records: Record[], rinfo: RecordInfo) => void——

once(event: 'records', listener: (records: Record[], rinfo: RecordInfo) => void): this

Overloads:

once(event: 'records', listener: (records: Record[], rinfo: RecordInfo) => void): this
once(event: 'error', listener: (err: Error) => void): this
once(event: 'ready', listener: () => void): this
once(event: 'close', listener: () => void): this

Parameters

ParameterTypeDefaultDescription
event'records'——
listener(records: Record[], rinfo: RecordInfo) => void——

query(name: string, type?: number): void

Sends an mDNS query for name.

Parameters

ParameterTypeDefaultDescription
namestring—The DNS name to query for, for example '_http._tcp.local'.
type?number—The DNS record type to request (default TYPE.PTR).

socket: object | null

The underlying UDP socket, or null before the resource has opened.

Discovery

new Discovery(opts?: DiscoveryOptions)

Discovers instances of a specific mDNS service (such as 'googlecast' or 'http') by periodically querying for it and parsing SRV, TXT, and address records into Service objects. Extends MDNS; subclass and override _parseService to customize how records are turned into a Service for a given service type.

Parameters

ParameterTypeDefaultDescription
opts?DiscoveryOptions—Options; see DiscoveryOptions.

discover(opts?: { first?: boolean; timeout?: number }): Promise<Service[]>

Queries for the configured service every 2 seconds until timeout milliseconds elapse (default 10000), or resolves early when opts.first is set and a service has been found.

Parameters

ParameterTypeDefaultDescription
opts?{ first?: boolean; timeout?: number }—Options: timeout is how long, in milliseconds, to keep querying before resolving (default 10000); set first to resolve as soon as the first service is found instead of waiting out the timeout.

Returns Promise<Service[]> — The discovered Service objects — a single-element array when opts.first resolved early.

emit(event: 'service', service: Service): boolean

Overloads:

emit(event: 'service', service: Service): boolean
emit(event: 'records', records: Record[], rinfo: RecordInfo): boolean
emit(event: 'error', err: Error): boolean
emit(event: 'ready'): boolean
emit(event: 'close'): boolean

Parameters

ParameterTypeDefaultDescription
event'service'——
serviceService——

off(event: 'service', listener: (service: Service) => void): this

Overloads:

off(event: 'service', listener: (service: Service) => void): this
off(event: 'records', listener: (records: Record[], rinfo: RecordInfo) => void): this
off(event: 'error', listener: (err: Error) => void): this
off(event: 'ready', listener: () => void): this
off(event: 'close', listener: () => void): this

Parameters

ParameterTypeDefaultDescription
event'service'——
listener(service: Service) => void——

on(event: 'service', listener: (service: Service) => void): this

Overloads:

on(event: 'service', listener: (service: Service) => void): this
on(event: 'records', listener: (records: Record[], rinfo: RecordInfo) => void): this
on(event: 'error', listener: (err: Error) => void): this
on(event: 'ready', listener: () => void): this
on(event: 'close', listener: () => void): this

Parameters

ParameterTypeDefaultDescription
event'service'——
listener(service: Service) => void——

once(event: 'service', listener: (service: Service) => void): this

Overloads:

once(event: 'service', listener: (service: Service) => void): this
once(event: 'records', listener: (records: Record[], rinfo: RecordInfo) => void): this
once(event: 'error', listener: (err: Error) => void): this
once(event: 'ready', listener: () => void): this
once(event: 'close', listener: () => void): this

Parameters

ParameterTypeDefaultDescription
event'service'——
listener(service: Service) => void——

service: string

The mDNS service name being discovered.

services: Map<string, Service>

A map of discovered services, keyed by service uid, accumulated since the last discover() call.

Constants and variables

TYPE

TYPE: {
    readonly A: 1
    readonly PTR: 12
    readonly TXT: 16
    readonly AAAA: 28
    readonly SRV: 33
  }

DNS record type numbers used in mDNS queries and records, per RFC 6762: A, PTR, TXT, AAAA, and SRV.

MDNS_ADDR: '224.0.0.251'

The IPv4 multicast address used for mDNS, 224.0.0.251, per RFC 6762.

MDNS_PORT: 5353

The UDP port used for mDNS, 5353, per RFC 6762.

Types

RecordInfo

interface RecordInfo {
  address: string
  port: number
  family: 'IPv4' | 'IPv6'
  size: number
}

The remote address information for a received mDNS packet: address, port, family, and the packet size in bytes.

SRVData

interface SRVData {
  priority: number
  weight: number
  port: number
  target: string
}

The parsed data of an SRV record: priority, weight, port, and target hostname.

TXTData

interface TXTData {
}

The parsed key/value pairs of a TXT record. A key with no = in its entry is stored with the value true.

Record

interface Record {
  name: string
  type: number
  class: number
  flush: boolean
  ttl: number
  data: string | TXTData | SRVData | Buffer
}

A single parsed DNS resource record from an mDNS response: name, type, class, the flush cache-flush bit, ttl, and the type-specific data.

Service

interface Service {
  uid: string
  name: string
  address: string
  addresses: {
      ipv4: string | null
      ipv6: string[]
    }
  port: number
  target: string
  txt: TXTData
}

A discovered service: its unique id, name, resolved address, all known addresses (IPv4 and IPv6), port, SRV target hostname, and txt record data.

MDNSOptions

interface MDNSOptions {
  debug?: boolean
  iface?: string
}

Options for MDNS. debug logs internal activity to the console. iface is the IPv4 address of the network interface to bind multicast membership on; required on Android, where it must be the WiFi interface IP so the kernel delivers mDNS responses on the correct interface.

DiscoveryOptions

interface DiscoveryOptions {
  service?: string
  debug?: boolean
  iface?: string
}

Options for Discovery, extending MDNSOptions with service, the mDNS service name to query for (for example 'googlecast').

See also

bare-posix

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On this page

Usage
Low-level mDNS queries
Service discovery
Extending for specific services
API
MDNS
new MDNS(opts?: MDNSOptions)
debug: boolean
emit(event: 'records', records: Record[], rinfo: RecordInfo): boolean
off(event: 'records', listener: (records: Record[], rinfo: RecordInfo) => void): this
on(event: 'records', listener: (records: Record[], rinfo: RecordInfo) => void): this
once(event: 'records', listener: (records: Record[], rinfo: RecordInfo) => void): this
query(name: string, type?: number): void
socket: object | null
Discovery
new Discovery(opts?: DiscoveryOptions)
discover(opts?: { first?: boolean; timeout?: number }): Promise<Service[]>
emit(event: 'service', service: Service): boolean
off(event: 'service', listener: (service: Service) => void): this
on(event: 'service', listener: (service: Service) => void): this
once(event: 'service', listener: (service: Service) => void): this
service: string
services: Map<string, Service>
Constants and variables
TYPE
MDNS_ADDR: '224.0.0.251'
MDNS_PORT: 5353
Types
RecordInfo
SRVData
TXTData
Record
Service
MDNSOptions
DiscoveryOptions
See also