udp

import {bind} from 'mikro/udp'

UDPUser Datagram Protocol sockets for IPv4 and IPv6. The module unblocks CoAPConstrained Application Protocol, mDNSMulticast DNS / DNS-SDDNS Service Discovery, NTPNetwork Time Protocol-style protocols, and custom binary protocols between mikrojs nodes. UDPUser Datagram Protocol itself is link-agnostic, so it works equally over WiFi STAStation (WiFi mode), WiFi APAccess Point, or future Thread / Ethernet.

Usage

import {bind} from 'mikro/udp'

const result = await bind({port: 5683})
if (!result.ok) {
  console.error('bind failed:', result.error)
} else {
  const socket = result.value

  socket.onMessage.subscribe(({msg, from}) => {
    console.log('%d bytes from %s:%d', msg.length, from.address, from.port)
  })

  await socket.send('hello', {address: '192.168.1.42', port: 5683, family: 'ipv4'})
}

Functions

bind(options)

bind(options: BindOptions): Promise<Result<UdpSocket, UdpError>>

Creates a UDPUser Datagram Protocol socket and binds it to a local address and port. Default is dual-stack (accepts both IPv4 and IPv6). Pass port: 0 for an ephemeral port; the actual port is readable on socket.port.

// Dual-stack on an ephemeral port
const r = await bind({port: 0})

// IPv4 only on a specific port
const v4 = await bind({port: 5683, family: 'ipv4'})

// Bind to a specific local address
const local = await bind({port: 0, address: '192.168.1.10', family: 'ipv4'})

Socket methods

socket.send(data, to)

send(data: Uint8Array | string, to: PeerAddress): Promise<Result<void, UdpError>>

Sends a single datagram. String data is UTFUnicode Transformation Format-8 encoded. The to argument must include family so the address can be parsed unambiguously.

const result = await socket.send('ping', {
  address: '192.168.1.42',
  port: 5683,
  family: 'ipv4',
})

socket.joinMulticastGroup(group)

joinMulticastGroup(group: {address: string}): Result<void, UdpError>

Joins an IPv4 or IPv6 multicast group. The socket's family determines which group type is accepted. An IPv4 interface (for example connected WiFi) must be up before joining an IPv4 group.

// mDNS multicast group
socket.joinMulticastGroup({address: '224.0.0.251'})

// CoAP all-nodes IPv6 group
socket.joinMulticastGroup({address: 'ff02::fd'})

socket.leaveMulticastGroup(group)

leaveMulticastGroup(group: {address: string}): Result<void, UdpError>

socket.close()

close(): void

Closes the socket. Idempotent. Subsequent send calls resolve to {name: 'Closed'}. A socket stays open until you call close(), even when your code no longer refers to it. Call close() to release the file descriptor.

Socket properties

Property	Type	Description
port	number	Actual bound port (resolved when bind was called with 0)
family	'ipv4' | 'ipv6' | 'dual'	Address family the socket was opened with
dropped	number	Counter of inbound datagrams dropped (see below)
onMessage	Observable<UdpMessage>	Stream of inbound datagrams. Subscribe to start receiving

Receiving

socket.onMessage is an Observable<UdpMessage> (see mikro/observable). Subscribe to receive packets — each emission is {msg, from} with a freshly allocated Uint8Array and a PeerAddress describing the sender. The first subscribe attaches the native dispatch; the last unsubscribe() detaches it again.

socket.onMessage.subscribe(({msg, from}) => {
  const text = new TextDecoder().decode(msg)
  console.log('%s:%d -> %s', from.address, from.port, text)
})

The receive buffer is 1500 bytes (typical Ethernet MTUMaximum Transmission Unit). Datagrams larger than that are dropped rather than truncated and increment socket.dropped. This covers all common protocols (CoAPConstrained Application Protocol is capped at 1152 bytes by spec; mDNSMulticast DNS, DNSDomain Name System, SNTPSimple Network Time Protocol all stay well under the MTUMaximum Transmission Unit).

Backpressure

Each socket has a bounded receive queue (default 8). When full, the newest datagram is dropped and socket.dropped is incremented. There is no separate drop event; applications that care can poll the counter periodically.

// Larger queue for a busy responder
const r = await bind({port: 5683, recvQueue: 32})

socket.dropped also increments when a packet arrives but no subscriber is attached to onMessage, or when a datagram is larger than the receive buffer.

Address normalization

Addresses are exposed in canonical form on receive:

• IPv4: 192.168.1.1 (v4-mapped v6 like ::ffff:192.168.1.1 is normalized back to plain v4).
• IPv6 global / mesh-local: fd00:db8::1 (RFCRequest For Comments 5952 canonical).
• IPv6 link-local with scope: fe80::1%2 (numeric interface index).

Addresses passed to send and bind accept the same forms, including the %scope suffix on link-local IPv6.

Types

BindOptions

interface BindOptions {
  port: number // 0 = ephemeral
  address?: string // local address (default: wildcard)
  family?: 'ipv4' | 'ipv6' // default: dual-stack v6
  recvQueue?: number // default: 8
}

PeerAddress

interface PeerAddress {
  address: string
  port: number
  family: 'ipv4' | 'ipv6'
}

Errors

UdpError

Variant	Fields	Description
BindFailed	message	Generic bind failure (an invalid address, for example)
AddressInUse	—	Local port already in use
SendFailed	message	Generic send failure (an invalid peer, for example)
MessageTooLarge	—	Datagram exceeded the path MTUMaximum Transmission Unit
NotReachable	—	No route to host or interface down
OutOfMemory	—	lwIP / kernel out of buffer memory
JoinGroupFailed	message	Multicast join failed (interface down or invalid)
LeaveGroupFailed	message	Multicast leave failed
Closed	—	Operation on a closed socket
NotBound	—	Operation on a socket that was never bound