nsd

A Flutter plugin for network service discovery and registration (aka NSD / DNS-SD / Bonjour / mDNS).

Basic Usage

Service Discovery

import 'package:nsd/nsd.dart';

final discovery = await startDiscovery('_http._tcp');
discovery.addListener(() {
  // discovery.services contains discovered services
});

// ...

await stopDiscovery(discovery);

or alternatively:

discovery.addServiceListener((service, status) {
  if (status == ServiceStatus.found) {
    // put service in own collection, etc.
  }
});

Service Registration

import 'package:nsd/nsd.dart';

final registration = await register(
  const Service(name: 'Foo', type: '_http._tcp', port: 56000));

// ...

await unregister(registration);

Permissions

Android

Add the following permissions to your manifest:

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.CHANGE_WIFI_MULTICAST_STATE" />

iOS

Add the following permissions to your Info.plist (replace service type with your own):

<key>NSLocalNetworkUsageDescription</key>
<string>Required to discover local network devices</string>
<key>NSBonjourServices</key>
<array>
    <string>_http._tcp</string>
</array>

Example application

The plugin includes an example application that can be used to start multiple discoveries and register multiple services. It will discover its own services but also other services of type _http._tcp in the local network, such as the printer in the screenshot above.

Use the action button to add a discovery or register a new service.
Swipe the cards left or right to dismiss a discovery or service.
The application log will show the calls and callbacks platform side vs. native side.
The source code demonstrates how to use the discovery object as a ChangeNotifier.

Minimum OS Requirements

Android: API level 21 (Android 5.0)
iOS: 12.0
macOS: 10.11 (El Capitan)
Windows 10 (19H1/1903) (Mai 2019 Update)

Advanced Usage

Get IP Addresses for Service

First, do you really need the IP address? If you just want to connect to the service, the host name that is supplied with the service should do just fine. In fact, connecting by host name is recommended on the Apple Developer Forums.

If you do need the IP address, you can configure automatic ip lookup for your discovery like this:

final discovery = await startDiscovery(serviceType, ipLookupType: IpLookupType.any);

Each discovered service will now have a list of IP addresses attached to it.

Discover All Services of All Types on Local Network

The current way to do this would be:

Start discovery using special service type _services._dns-sd._udp
Receive list of all service types in network
Do discovery for each service type

Start the discovery like this:

final discovery = await startDiscovery('_services._dns-sd._udp', autoResolve: false);

The autoResolve flag is important because the results are not real services and cannot be resolved. The discovery.services list will then be populated with the answers. The Service instances returned will contain service type info, like so:

{service.type: _tcp.local, service.name: _foo, ...}
{service.type: _tcp.local, service.name: _bar, ...}

The first component of the service type (e.g. _foo) is contained in the service name attribute, the second component of the service type (e.g. _tcp) is contained in the service type attribute.

Even though using a service structure to represent a service type feels like a hack, it seems to be consistent on Android / macOS / iOS platform APIs. Since they are all doing it, the plugin has the same behavior.

Note: this currently doesn't function 100% on Windows platforms. While it will detect the types of services registered by other machines correctly, it will not detect types of services that were registered using the plugin.

Disable service name validation

Service names are validated by the plugin according to RFC 6335:

MUST be at least 1 character and no more than 15 characters long
MUST contain only US-ASCII ANSI.X3.4-1986 letters 'A' - 'Z' and 'a' - 'z', digits '0' - '9', and hyphens ('-', ASCII 0x2D or decimal 45)
MUST contain at least one letter ('A' - 'Z' or 'a' - 'z')
MUST NOT begin or end with a hyphen
hyphens MUST NOT be adjacent to other hyphens

If you are getting the error message "Service type must be in format..." but you still want to work with service names that do not conform to the rules, you can disable service name validation entirely:

disableServiceTypeValidation(true);

Be aware that some network environments might not support non-conformant service names.

Enable Debug Logging

In order to help debugging, logging can be enabled for individual topics. For example

enableLogging(LogTopic.errors);
enableLogging(LogTopic.calls);

will log errors and all calls to the native side (and their callbacks), which often yields useful information.

Contributors

lxp-git - wrote the Windows prototype!

Projects using nsd

🎮 Tic Tac Toe Local Multiplayer Game for Android by Laks Castro

nsd