Networking

Copyright 2017-2023 Moddable Tech, Inc.
Revised: August 31, 2023

Table of Contents

• Socket
• Listener
• HTTP
  • Request
  • Server
• WebSocket
  • Client
  • Server
• Net
• WiFi
• SNTP
• DNS
  • Constants
  • Parser
  • Serializer
  • Server
• MDNS
• Telnet
• Ping
• MQTT

class Socket

• Source code: socket
• Relevant Examples: socket, socketreadwrite

The Socket class implements a non-blocking network connection using a TCP or a UDP socket.

import {Socket, Listener} from "socket";

constructor(dictionary)

The Socket constructor takes a single argument, a dictionary of initialization parameters. The constructor immediately initiates a connection to the remote host.

If the IP address is known, use the address property in the dictionary.

let socket = new Socket({address "17.172.224.47", port: 80});

To initiate a connection to a remote server specified by a host name, include host and port properties in the dictionary. The socket resolves the host name to an IP address.

let host = "www.moddable.tech";
let port = 80;
let socket = new Socket({host, port});

By default a new socket uses TCP. The socket kind can be set in the dictionary:

let tcp = new Socket({host: "moddable.tech", port: 1234, kind: "TCP"});
let udp = new Socket({port: 123, kind: "UDP"});
let raw = new Socket({kind: "RAW", protocol: 1});

To accept a new connection request from a Listener, specify the listener property in the dictionary:

let listener = new Listener({port: 80});
let socket = new Socket({listener});

For TCP sockets, the dictionary supports two option properties:

• noDelay - A Boolean value to control whether the Nagle Algorithm is enabled (TCP_NODELAY). It is enabled by default on most platforms. For some situations, better write performance may be achieved by disabling it.

	{...., noDelay: true}

• keepalive - An object to control the keep alive behavior of the socket. The idle and interval properties are in milliseconds. For example:

	{...., keepalive: {idle: 60 * 1000, interval: 30 * 1000, count: 4}}

close()

The close function immediately terminates the socket, freeing all resources associated with the socket.

socket.close();

read(type [, until])

The read function receives data from the socket. Data is only available to read inside the callback function when it receives a data message; attempts to read data at other times will fail.

To read all available data into a String:

let string = this.read(String);

To read all available data into an ArrayBuffer:

let buffer = this.read(ArrayBuffer);

To read one byte into a Number:

let byte = this.read(Number);

To read 12 bytes into a String or ArrayBuffer:

let string = this.read(String, 12);
let buffer = this.read(ArrayBuffer, 12);

To read up to the next space character into String or ArrayBuffer. If there is no space character found, the remainder of the available data is read:

let string = this.read(String, " ");
let buffer = this.read(ArrayBuffer, " ");

To skip data in the read buffer, read to null:

this.read(null, 5);		// skip ahead 5 bytes

To skip to the next carriage-return (or the end of the buffer, if none found):

this.read(null, "\n");

When reading to null, the return value is the count of bytes skipped.

To determine the number of available bytes remaining in the buffer, call read with no arguments:

let bytesAvailable = this.read();

write(data [, data1, ...])

The write function sends data on the socket. One or more arguments may be passed to write for transmission.

For a TCP socket, all parameters are data to be transmitted.

socket.write("Hello");
socket.write(32);
socket.write("world.", 13);
socket.write(JSON.stringify(obj));

String and ArrayBuffer values are transmitted as-is. A Number value is transmitted as a byte.

If the socket has insufficient buffer space to transmit the data, none of the data is sent. To determine the number of bytes that can be transmitted, call write with no arguments:

let bytesToSend = socket.write();

For a UDP socket, the first two parameters are the IP address and port to transmit the packet to. The third parameters is the data to transmit as an ArrayBuffer:

socket.write("1.2.3.4", 1234, packet);

For a RAW socket, the first parameter is IP address to transmit the packet to. The second parameter is the data to transmit as an ArrayBuffer:

socket.write("1.2.3.4", packet);

It is more efficient to make a single write call with several parameters instead of multiple calls to write.

get(what)

The get method returns state information about the socket. The what argument is a string indicating the state requested. If the state is unavailable, get returns undefined.

callback(message [, value])

The user of the socket receives status information through the callback function. The first argument to the callback is the messages identifier. Positive message values indicate normal operation and negative message values indicate an error. Depending on the message, there may be additional arguments.

For UDP sockets, the callback for dataReceived has three additional arguments after the message identifier . The first is the number of bytes available to read, as with TCP sockets. The second is a string containing the IP address of the sender. The third is the port number of the sender.

callback(message, byteLength, remoteIP, remotePort) {}
}

For RAW sockets, the callback for dataReceived has two additional arguments after the message identifier . The first is the number of bytes available to read, as with TCP sockets. The second is a string containing the IP address of the sender.

callback(message, byteLength, remoteIP) {}

Example: HTTP GET

The following sample shows using the Socket object to make a simple HTTP GET request and trace the response, including headers, to the console. This example is not intended as a useful HTTP client.

let host = "www.example.com";
let port = 80;
let socket = new Socket({host, port});

socket.callback = function(message, value)
{
	if (1 == message) {
		this.write("GET / HTTP/1.1\r\n");
		this.write("Host: ", host, "\r\n");
		this.write("Connection: close\r\n");
		this.write("\r\n");
	}
	else if (2 == message)
		trace(this.read(String));
}

class Listener

• Source code: socket
• Relevant Examples: socketlistener

The Listener class implements a network socket listener to accept new TCP connections. The Listener class is used together with the Socket class.

import {Socket, Listener} from "socket";

constructor(dictionary)

The Listener constructor takes a single argument, a object dictionary of initialization parameters.

To listen, use the port property to specify the port to listen on:

let telnet = new Listener({port: 23});

callback()

The user of the listener is notified through the callback function. The callback function accepts the connection request and instantiates a new socket by invoking the Socket constructor with the listener instance.

telnet.callback = function() {
	let socket = new Socket({listener: this});
	...
}

Example: HTTP server

The following example implements a trivial HTTP server using Listener and Socket. The server is truly trivial, not even parsing the client request.

let count = 0;
let listener = new Listener({port: 80});
listener.callback = function() {
	let socket = new Socket({listener});
	let message = `Hello, server ${++count}.`;
	socket.write("HTTP/1.1 200 OK\r\n");
	socket.write("Connection: close\r\n");
	socket.write(`Content-Length: ${message.length}\r\n`);
	socket.write("Content-Type: text/plain\r\n");
	socket.write("\r\n");
	socket.write(message);
	socket.close();
}

class HTTP Request

• Source code: http
• Relevant Examples: httpget, httppost, httpsget, and many more

The HTTP Request class implements a client for making HTTP requests. It is built on the Socket class. Like the Socket class, the HTTP Request uses a dictionary-based constructor and a single callback.

import {Request} from "http"

constructor(dictionary)

A new HTTP Request is configured using a dictionary of properties. The dictionary is a super-set of the Socket dictionary.

The complete list of properties the HTTP Request adds to the Socket dictionary is:

To request the root "/" resource on port 80 as a String:

let request = new Request({host: "www.example.com", response: String});

To request the "/info.dat" resource from port 8080 as an ArrayBuffer:

let request = new Request({host: "www.example.com", path: "/info.dat", port: 8080, response: ArrayBuffer});

To request the "/weather.json" resource from a device with IP address "192.0.1.15" as a String object:

let request = new Request({address: "192.0.1.15", path: "/weather.json", response: String});

To issue a DELETE request, set the method property in the dictionary:

let request = new Request({address: "192.0.1.15", path: "/resource/to/delete", method: "DELETE"});

close()

The close function immediately terminates the HTTP request, freeing the socket and any other associated memory.

request.close();

read(type [, until])

The read function behaves exactly like the read function of the Socket class. The read function can only be called inside the callback providing a response body fragment.

Note: The HTTP read function implentation does not currently support passing a String for the until argument on a response that uses chunked transfer-encoding.

callback(message, val1, val2)

The user of the Request object receives status information through the callback function. The callback receives messages and, for some messages, additional data values. Non-negative message values indicate normal operation and negative message values indicate an error.

class HTTP Server

• Source code: http
• Relevant Examples: httpserver, httpserverbmp, httpserverchunked, httpserverputfile

The HTTP Server class implements a server to respond to HTTP requests. It is built on the Socket class. Like the Socket class, the HTTP Server class uses a dictionary-based constructor and a single callback.

import {Server} from "http"

constructor(dictionary)

A new HTTP server is configured using a dictionary of properties. The dictionary is a super-set of the Socket dictionary.

To open an HTTP server, on the default port (80):

let server = new Server({});

To open an HTTP server on port 8080:

let server = new Server({port: 8080});

close()

The close function immediately terminates the HTTP server, freeing the server listener socket and any other associated memory.

server.close();

Note: The close function does not close active connections to the server.

detach(connection)

The detach function accepts an active HTTP connection of the server instance and removes it from the server, returning the socket instance of the connection. This is useful for implementing an HTTP endpoint that accepts both HTTP and WebSocket connections by allowing the existing connection of HTTP server to be handed off to the WebSocket server.

server.detach(connection);

callback(message, val1, val2)

The user of the server receives status information through the callback function. The callback receives messages and, for some messages, additional data values. Positive message values indicate normal operation and negative message values indicate an error.

A new HTTP Request is instantiated for each incoming request. The callback is invoked with this set to the callback instance for the request. The callback function may attach properties related to handling a specific request to this, rather than using global variables, to ensure there are no state collisions when there are multiple active requests.

Example: Simple HTTP server

The following example implements an HTTP server that responds to all requests by echoing the requested path.

(new Server({})).callback = function(message, value) {
	switch (message) {
		case 2:		// HTTP status line received
			this.path = value;
			break;

		case 8:		// prepare response body
			return {headers: ["Content-type", "text/plain"], body: this.path};
	}
}

The server instance has a single callback function which responds to messages corresponding to the steps in fulfilling an HTTP request. A new request instance is created for each request, so the callback receives a unique this for each request. In this example, when the HTTP status line of a new request is received (message 2), the callback stores the path of the request. When the server is ready to transmit the body of the response (message 8), the callback returns the HTTP headers and response body (the path, in this case). The server adds the Content-Length header.

Example: HTTP Server with chunked response

The following example implements an HTTP server that responds to requests with a sequence of random numbers of random length.

(new Server({})).callback = function(message, value) {
	switch (message) {
		case 8:	// prepare response body
			return {headers: ["Content-type", "text/plain"], body: true};

		case 9:	// provide response body fragment
			let i = Math.round(Math.random() * 20);
			if (0 == i)
				return;
			return i + "\n";
	}
}

In this example, when the server is ready to transmit the response body (message 8), the callback returns the HTTP headers, and true for the body indicating the response body will be provided in fragments. In this case, the server adds a Transfer-encoding header with the value chunked. When the server is ready to transmit the next chunk of the response, the callback is invoked (message 9) to return the chunk. In this example, it returns a random number. When the random number is 0, the server returns undefined indicating the request is complete.

Example: HTTP Server receiving a JSON PUT

The following example implements an HTTP server that receives a JSON request, and echoes the JSON back in the response body.

(new Server({})).callback = function(message, value) {
	switch (message) {
		case 4:		// request headers received, prepare for request body
			return String;

		case 6:		// request body received
			this.jsonRequest = JSON.parse(value);
			trace(`received JSON: ${value}\n`);
			break;

		case 8:		// prepare response body
			return {headers: ["Content-type", "application/json"],
						body: JSON.stringify(this.jsonRequest)};
	}
}

The callback is invoked when the request headers have been received (message 4), and returns String indicating it wants to receive the request body as a String object. When the complete request body has been received, the callback is invoked (message 6). The callback retains a reference to the JSON object in the jsonRequest property of the request instance. When the callback is invoked to transmit the response body (message 8), it serializes the JSON object to a string to transmit as the message body.

Example: HTTP Server streaming PUT to file

The following example implements an HTTP server that receives PUT requests, and streams the request body to a file using the HTTP request path as the local file path.

import {File} from "file";

(new Server({})).callback = function(message, value) {
	switch (message) {
		case 2:								// request status received
			let path = value;				// file path is HTTP path
			File.delete(path);
			this.file = new File(path, true);
			break;

		case 4:								// prepare for request body
			return true;					// provide request body in fragments

		case 5:								// request body fragment
			this.file.write(this.read(ArrayBuffer));
			break;

		case 6:								// request body received
			this.file.close();
			break;
	}
}

To try the code, use the curl tool as follows, substituting the file path and IP address as necessary:

curl --data-binary "@/users/hoddie/projects/test.txt"  http://192.168.1.37/test.txt

class WebSocket Client

• Source code: websocket
• Relevant Examples: websocketclient

The WebSocket Client class implements a client for communicating with a WebSocket server. It is built on the Socket class. Like the Socket class, the WebSocket Client uses a dictionary-based constructor and a single callback.

import {Client} from "websocket"

The WebSocket client implementation is designed for sending and receiving small messages. It has the following limitations:

• Each message must be a single frame. Fragmented messages are not supported.
• Messages are not masked when sent.

constructor(dictionary)

A new WebSocket Client is configured using a dictionary of properties. The dictionary is a super-set of the Socket dictionary.

The complete list of properties the WebSocket Client adds to the Socket dictionary is:

To connect to a server on port 80 at the root path "/":

let ws = new Client({host: "echo.websocket.org"});

To connect to a server by IP address on port 8080:

let ws = new Client({address: "174.129.224.73", port: 8080});

close()

The close function immediately terminates the WebSocket connection, freeing the socket and any other associated memory.

ws.close();

write(message)

The write function transmits a single WebSockets message. The message is either a String, which is sent as a text message, or an ArrayBuffer, which is sent as a binary message.

ws.write("hello");
ws.write(JSON.stringify({text: "hello"}));

callback(message, value)

The user of the WebSocket client receives status information through the callback function. The callback receives messages and, for some messages, a data value. Positive message values indicate normal operation and negative message values indicate an error.

class WebSocket Server

• Source code: websocket
• Relevant Examples: websocketserver

The WebSocket Server class implements a server for communicating with WebSocket clients. It is built on the Socket class. Like the Socket class, the WebSocket Server uses a dictionary-based constructor and a single callback.

import {Server} from "websocket"

The WebSocket server implementation is designed for sending and receiving small messages. It has the following limitations:

• Each message must be a single frame. Fragmented messages are not supported.

constructor(dictionary)

A new WebSocket Server is configured using a dictionary of properties. The dictionary is a super-set of the Listener dictionary. The server is a Socket Listener. If no port is provided in the dictionary, port 80 is used. If port is set to null, no listener is created which is useful when sharing a listener with an http server (see attach below).

At this time, the WebSocket Server does not define any additional properties for the dictionary.

let ws = new Server({});

close()

The close function immediately terminates the WebSocket server listener, freeing the socket and any other associated memory. Active connections remain open.

ws.close();

attach(socket)

The attach function creates a new incoming WebSockets connection from the provided socket. The server issues the Server.connect callback and then performs the WebSockets handshake. The status line has been read from the socket, but none of the HTTP headers have been read as these are required to complete the handshake.

See the httpserverwithwebsockets for an example of sharing a single listener socket between the HTTP and WebSockets servers.

callback(message, value)

The WebSocket server callback is the same as the WebSocket client callback with the addition of the "Socket connected" (1 or Server.connect) message. The socket connected message for the server is invoked when the server accepts a new incoming connection.

The value of this is unique for each connection made to the server. Messages cannot be sent until after the callback receives the WebSocket handshake complete message (Server.handshake).

The this instance of the callback has the same write and close methods as the WebSocket Client. These methods are used to send data and to close the connection.

Note: Text and binary messages received with the mask bit set are unmasked by the server before delivering them to the callback.

class Net

• Source code: net
• Relevant Examples: net

The Net class provides access to status information about the active network connection.

import Net from "net";

static get(property [, interface])

The get function returns properties of the active network connection.

The following properties are available:

trace(`Connected to Wi-Fi access point: ${Net.get("SSID")}\n`);

For a device operating as both a Wi-Fi station (client) and a Wi-Fi access point, the static get method accepts an optional second argument to indicate if the request is for the station or access point interface. The interface accepts values of "station" and "ap". It is used for the IP and MAC properties.

On ESP32, the optional second argument can also be used to explicitly request information about the Ethernet interface by providing the value "ethernet".

trace(`IP default ${Net.get("IP")}\n`);
trace(`IP station ${Net.get("IP", "station")}\n`);
trace(`IP AP ${Net.get("IP", "ap")}\n`);

In station mode, the default value for the interface is "station"; in access point mode, "ap". In the combined station and access point mode, there is no default value (because it is ambiguous). Requesting the IP or MAC properties in this mode returns undefined.

static resolve(host, callback)

The resolve function performs performs an asynchronous DNS look-up for the specified host and invokes the callback to deliver the result.

Net.resolve("moddable.tech", (name, address) => trace(`${name} IP address is ${address}\n`);

The IP address is provided as a String in dotted IP address notation. If host cannot be resolved, the address parameter is undefined.

The DNS implementation in lwIP supports a limited number of simultaneous DNS look-ups. The number depends on the specific platform deployment. On the ESP8266 it is 4. If the DNS resolve queue is full, resolve throws an exception.

class WiFi

• Source code: wifi
• Relevant Examples: wifiaccesspoint, wifiscan

The WiFi class provides access to use and configure the Wi-Fi capabilities of the host device.

import WiFi from "wifi";

constructor(dictionary, callback)

The WiFi constructor takes a single argument, a dictionary of initialization parameters. The constructor begins the process of establishing a connection.

The dictionary always contains the required ssid property with the name of the base station to connect to. The optional password property is included when the base station requires a password. When the optional bssid property is included, it may accelerate connecting to Wi-Fi on device targets that support it.

The connection process is asynchronous and may be monitored using the callback function.

The following example begins the process of connecting to a Wi-Fi access point and waits for the connection to succeed with an IP address being assigned to the device.

let monitor = new WiFi({ssid: "My Wi-Fi", password: "secret"}, msg => {
	switch (msg) {
		case WiFi.connected:
			break; // still waiting for IP address
		case WiFi.gotIP:
			trace(`IP address ${Net.get("IP")}\n`);
			break;
		case WiFi.disconnected:
			break;  // connection lost
	}
});

The following example initiates a connection to a Wi-Fi access point with no password. Because there is no callback function to monitor connection progress, polling is necessary to determine when the connection is ready. Poll by getting the IP address of the device using the Net class. When there is no connection, the results is undefined.

let monitor = new WiFi({ssid: "Open Wi-Fi"});

close()

The close function closes the connection between the WiFi instance and the underlying process managing the device's connection to the network. In other words, it prevents future calls to the callback function, but it does not disconnect from the network.

monitor.close();

static scan(dictionary, callback)

The scan static function initiates a scan for available Wi-Fi access points.

The dictionary parameter supports two optional properties:

The callback function is invoked once for each access point found. When the scan is complete, the callback function is invoked a final time with a null argument.

WiFi.scan({}, item => {
	if (item)
		trace(`name: ${item.ssid}, password: ${item.authentication != "none"}, rssi: ${item.rssi}, bssid: ${(new Uint8Array(item.bssid)).join(".")}\n`);
	else
		trace("scan complete.\n");
});

The Wi-Fi scan runs for a fixed period of time, approximately two seconds. During that time, not all access points may be found. It may be necessary to call scan several times to create a complete list of visible access points.

Note: Only one scan may be active at a time. Starting a new scan while one is still active will throw an exception.

mode property

The mode property is set to 1 for station mode (e.g. device acts as Wi-Fi client), 2 for access point mode (e.g. device acts as Wi-Fi base station), and 3 for simultaneous operation of station and access point modes.

static connect(dictionary)

The connect function begins the process of establishing a connection. The connection process is asynchronous and may be monitored by polling Net.get("IP") or by creating a new WiFi instance. The dictionary contains either ssid or bssid properties indicating the base station to connect to, and an optional password.

WiFi.connect({ssid: "Moddable", password: "1234"});

Note: Calling WiFi.connect with no parameters disconnects. However, it is recommended to use WiFi.disconnect insteadm

static disconnect()

Disconnects from the current Wi-Fi base station

WiFi.disconnect();

static accessPoint(dictionary)

The accessPoint function configures the device as a Wi-Fi access point. Depending on the device, this may exit station mode.

The dictionary must include an ssid property, a string that gives the name of the access point.

The dictionary may optionally include the following properties:

WiFi.accessPoint({
	ssid: "Moddable Zero",
	password: "12345678"
});

class SNTP

• Source code: sntp
• Relevant Examples: sntp, ntpclient

The SNTP class implements an SNTP client (RFC 4330) to retrieve a real time clock value.

import SNTP from "sntp";

The SNTP client implementation fail-over mechanism allows additional servers to be queried in case of failure.

constructor(dictionary, callback)

The SNTP constructor takes a dictionary of properties and a callback function to receive information about the instance status.

The dictionary must include a host property, a string that gives the host name or IP address of the SNTP server.

The callback receives messages and, for some messages, a data value. Positive message values indicate normal operation and negative message values indicate an error.

Example: Retrieving the time

The following example retrieves the current time value from the NTP server at pool.ntp.org.

new SNTP({host: "pool.ntp.org"}, (message, value) => {
	if (1 === message)
		trace(`time value is ${value}\n`);
});

The SNTP constructor requires the host name or IP address of a time server. If a host name is provided, the SNTP client first resolves that to an IP address using Net.resolve.

class DNS constants

• Source code: dns

The DNS module contains constants that are useful when implementing code that interacts directly with the DNS protocol. It is used by the DNS Parser, DNS Serializer, and mDNS implementation.

import DNS from "dns";

• DNS.RR contains constants for resource record types, such as DNS.RR.PTR.
• DNS.OPCODE contains values for DNS.OPCODE.QUERY and DNS.OPCODE.UPDATE.
• DNS.CLASS contains values for DNS.CLASS.IN, DNS.CLASS.NONE, and DNS.CLASS.ANY.
• DNS.SECTION contains values that include DNS.QUESTION and DNS.ANSWER.

class DNS Parser

• Source code: dnsparser

The DNS Parser class extracts JavaScript objects from a binary DNS record.

import Parser from "dns/parser";

The DNS parser class parses and returns a single resource record at a time to minimize memory use. It has parsers for the resource data of A, AAAA, PTR, SRV, TXT resource record types.

Note: The DNS Parser is a low level class used to build higher level services, such as mDNS.

constructor(buffer)

The DNS Parser constructor is initialized with an ArrayBuffer containing a single DNS packet.

No validation is performed by the constructor. Errors, if any, are reported when extracting resource records.

questions(index)

Returns the question resource record corresponding to the index argument. Indices are numbered from 0. Returns null if index is greater than number of question records in the packet.

answers(index)

Returns the answer resource record corresponding to the index argument. Indices are numbered from 0. Returns null if index is greater than number of answer records in the packet.

authorities(index)

Returns the authority resource record corresponding to the index argument. Indices are numbered from 0. Returns null if index is greater than number of authority records in the packet.

additionals(index)

Returns the additional resource record corresponding to the index argument. Indices are numbered from 0. Returns null if index is greater than number of additional records in the packet.

Example: Parsing a DNS packet

DNS packets are typically received as UDP packets. The Socket object provides each DNS packet in an ArrayBuffer. The follow example creates a DNS parser instance for an ArrayBuffer:

let packet = new Parser(dnsPacket);

The Parser constructor does not validate the packet. If the packet is invalid, errors will be reported when extracting records from it.

Example: Reading header fields

The parser instance has properties for the id and flags fields in the DNS packet:

let id = packet.id;
let flags = packet.flags;

Example: Determining the number of records

The parser instance has properties that provide the number of resource records in each section.

let total = packet.questions + packet.answers + packet.authorities + packet.additionals;

Example: Extracting a resource record

A JavaScript object containing a single resource record is retrieved by calling the function corresponding to the resource record's section. The following example retrieves the second question resource record (indices start at 0):

let rr = packet.question(1);

There are also answers, authorities, and additionals functions.

class DNS Serializer

• Source code: dnsserializer

The DNS Serializer class implements a DNS record serializer.

import Serializer from "dns/serializer";

The DNS Serializer class is able to serialize A, NSEC, PTR, SRV, and TXT resource record types. Clients may perform their own serialization of other resource record types and provide the result to the DNS Serializer class to include in the generated DNS packet.

Note: The DNS Serializer is a low level class used to build higher level services, such as mDNS.

constructor(dictionary)

The DNS Serializer constructor accepts a dictionary with properties to configure the DNS packet to be created. The dictionary may contain the following properties:

add(section, name, type, clss, ttl, ...)

The add function adds a resource record to be serialized into the DNS packet. The first five arguments to add are the same for all resource records.

The optional data argument is used to build the resource data portion of the resource record. If not present, the resource data is empty. If it is an ArrayBuffer, its contents are used for the resource data. The data argument is interpreted these resource record types:

build()

The build function generates a DNS packet based on the previous calls to the serializer instance. The packet is returned as an ArrayBuffer.

Note: The current implementation does not compress QNAMES, resulting in a larger DNS packet than necessary.

Example: Building a DNS query

The following example uses the DNS Serializer to create a DNS packet querying for an A record for the "example.com" domain:

let serializer = new Serializer({query: true, opcode: DNS.OPCODE.QUERY});
serializer.add(DNS.SECTION.QUESTION, "example.com", DNS.RR.A, DNS.CLASS.IN);
let buffer = serializer.build();

The build function returns a DNS packet suitable for sending using the write function of the Socket class.

class DNS Server

• Source code: dnsserver
• Relevant Examples: dnsserver

The DNSServer class implements a simple DNS server.

import DNSServer from "dns/server";

The server is indicated for use in devices in Wi-Fi access point mode that wish to act as a captive portal. The DNS server is used to direct look-ups for certain domains to an IP address, typically the device running the DNS server.

constructor(callback)

The DNSServer constructor takes a single argument, a function to call when a look-up request is received. The callback receives two arguments. The first, message, is set to 1 when a look-up is performed. The second argument, value, is set to the name to be resolved when a look-up request is made.

let server = new DNSServer((message, value) => {
	...
});

close()

When the DNS server is no longer needed, call close to terminate it and free its resources.

server.close();

Example: Simple DNS server

The following example redirects all DNS look-ups to the IP address of the device running the server.

new DNSServer((message, value) => {
	if (1 === message)
		return Net.get("IP", "ap");
})

Note:: This example expects to be run on a Wi-Fi connection in access point mode. It passes "ap" for the interface argument to Net.get to retrieve the IP address for access point.

Example: DNS server for a single host name

The following example redirects all DNS look-ups for "example.com" to the IP address of the device running the server. All other look-ups are ignored.

new DNSServer((message, value) => {
	if ((1 == message) && ("example.com" == value))
		return Net.get("IP", 'ap");
})

class MDNS

• Source code: mdns
• Relevant Examples: discoverhttp, httpserver, ntpclient, ntpservice,

The MDNS class implements services for working with Multicast DNS discovery and services. It includes claiming .local names, advertising mDNS service availability, and scanning for available mDNS services.

import MDNS from "mdns";

constructor(dictionary [, callback])

The MDNS constructor takes a dictionary to configure the mDNS instance and an optional callback to receive information about the instance status.

If the dictionary contains a hostName property, the MDNS instance will attempt to claim the name in the .local domain on the active network connection. The hostName is not required to monitor for available mDNS services.

The callback receives messages and, for some messages, a data value. The message and value provide information on the claiming process. Positive message values indicate normal operation and negative message values indicate an error.

The following example shows how to claim the name "mydevice" on the local network.

const mdns = new MDNS({hostName: "mydevice"});

The claiming process takes some time, usually under one second. Claiming the name may not succeed because the name may already be in use. An optional callback function provides status on the claim:

const mdns = new MDNS({hostName: "mydevice"}, function(message, value) {
	switch (message) {
		case 1:
			trace(`MDNS - claimed hostname is "${value}"\n`);
			break;
		case 2:
			trace(`MDNS - failed to claim "${value}", try next\n`);
			break;
		default:
			if (message < 0)
				trace("MDNS - failed to claim, give up\n");
			break;
	}
});

monitor(serviceType, callback)

The monitor function continuously scans the network for mDNS services of the type indicated by the serviceType parameter.

The callback function is invoked for each unique service instance found and whenever a service announces changes to its TXT resource record. The first argument to the callback is the service type, for example "_http._tcp". The second is a dictionary that contains name, protocol, port, and txt properties describing the service.

The following example continuously monitors for _http._tcp services available on the local network:

mdns.monitor("_http._tcp", (service, instance) => {
	trace(`Found ${service}: ${instance.name}\n`);
});

add(service)

The add function registers an mDNS service description to be advertised. The service record contains the following properties:

add may only be called after the hostname claiming process has completed successfully.

The following example announces the availability of an _http._tcp service on port 80 of the current host.

mdns.add({
	name: "http",
	protocol: "tcp",
	port: 80,
	txt: {
		url: `/index.html`,
	}
});

update(service)

The update function tells the MDNS implementation that the contents of the TXT record have changed. This causes the new TXT record to be announced to the local network. The service object passed must be the same object provided to add.

let service = mdns.services[0];
service.txt["value"] = 123;
mdns.update(service);

remove(service) or remove(serviceType)

The remove function is used both to unregister the service and to cancel monitoring for a service type.

To unregister a service, pass the service description. This announces to the network that it is no longer available. The service object must be the same object provided to add.

mdns.remove(mdns.services[0]);

To cancel monitoring for a service type, pass the name of the service type.

mdns.remove("_http._tcp");

class Telnet

• Source code: telnet
• Relevant Examples: telnet

The Telnet class implements a simple telnet server. The commands supported by the telnet server are determined by the CLI classes registered with the Console module.

constructor(dictionary)

To start a telnet server, invoke the Telnet constructor:

The Telnet constructor takes a single argument, a dictionary. The dictionary has a single property, port, which indicates the port to listen on for new connections. If the port is not included in the dictionary, it defaults to 23.

let telnet = new Telnet({port: 2300});

close()

When the Telnet server is no longer needed, call close to terminate it and free its resources.

telnet.close();

class Ping

• Source code: ping
• Relevant Examples: ping

The Ping class implements the ping networking utility.

import Ping from "ping";

constructor(dictionary, callback)

The Ping constructor takes two arguments, a dictionary and a callback function.

The dictionary must contain the following properties:

The dictionary may optionally contain an interval parameter, which sets the interval between pings, in milliseconds. If none is specified, the default is 5000, or 5 seconds.

The user receives status information through the callback function. The callback receives messages and, for some messages, a data value and additional information in the etc parameter. Positive message values indicate normal operation and negative message values indicate an error.

The following example pings the server at example.com every 1000ms, tracing the results to the console.

let ping = new Ping({host: "example.com", id: 1, interval: 1000}, (message, value, etc) => {
	if (1 == message)
		trace(`${value} bytes from ${etc.address}: icmp_seq=${etc.icmp_seq}\n`);
}

close()

To stop pinging the host, call the close function.

ping.close();

class MQTT

• Source code: mqtt
• Relevant examples: mqttbasic, mqttsecure

The MQTT Client class implements a client that connects to an MQTT broker (server).

import Client from "mqtt";

constructor(dictionary)

A new MQTT Client is configured using a dictionary of properties. The dictionary must contain host and id properties; other properties are optional.

let mqtt = new Client({
	host: "test.mosquitto.org",
	id: "iot_" + Net.get("MAC"),
	user: "user name",
	password: ArrayBuffer.fromString("secret")
});

onReady()

The onReady callback is invoked when a connection is successfully established to the server. No messages may be published or subscriptions created before onReady is called.

mqtt.onReady = function () {
	trace("connection established\n");
}

subscribe(topic)

To subscribe to a topic, use the subscribe method. Your client can subscribe to multiple clients by calling subscribe more than once.

mqtt.subscribe("test/string");
mqtt.subscribe("test/binary");
mqtt.subscribe("test/json");

unsubscribe(topic)

Use the unsubscribe method to unsubscribe to a topic.

mqtt.unsubscribe("test/string");

onMessage(topic, data)

The onMessage callback is invoked when a message is received for any topic that your client has subscribed to. The topic argument is the name of the topic and the data argument is the complete message.

mqtt.onMessage = function(topic, data) {
	trace(`received message on topic "${topic}"\n`);
}

The data argument is an ArrayBuffer. For messages containing only UTF-8 text, you can convert it to a string using String.fromArrayBuffer.

mqtt.onMessage = function(topic, data) {
	trace(`received message on topic "${topic}"\n`);
	trace(`data: ${String.fromArrayBuffer(data)}\n`);
}

publish(topic, message)

To send a message to a topic, use the publish method. The message argument may be either a string or an ArrayBuffer.

mqtt.publish("test/string", "hello");
mqtt.publish("test/binary", Uint8Array.of(1, 2, 3).buffer);

To publish JSON, first convert it to a string.

mqtt.publish("test/json", JSON.stringify({
	message: "hello",
	version: 1
}));

onClose()

The onClose callback is invoked when the connection is lost, because of a network error or because the MQTT broker closed the connection.

mqtt.onClose = function() {
	trace("connection lost\n");
}