mDNS Management

Overview

Multicast DNS (mDNS) provides functions such as adding, removing, discovering, and resolving local services on a LAN.

Local service: a service provider on a LAN, for example, a printer or scanner.

Typical mDNS management scenarios include:

Managing local services on a LAN, such as adding, removing, and resolving local services.
Discovering local services and listening to the status changes of local services of the specified type through the DiscoveryService object.

NOTE To maximize the application running efficiency, most API calls are called asynchronously in callback or promise mode. The following code examples use the callback mode. For details about the APIs, see mDNS Management.

The following describes the development procedure specific to each application scenario.

Available APIs

For the complete list of APIs and example code, see mDNS Management.

Type	API	Description
ohos.net.mdns	addLocalService(context: Context, serviceInfo: LocalServiceInfo, callback: AsyncCallback<LocalServiceInfo>): void	Adds an mDNS service. This API uses an asynchronous callback to return the result.
ohos.net.mdns	removeLocalService(context: Context, serviceInfo: LocalServiceInfo, callback: AsyncCallback<LocalServiceInfo>): void	Removes an mDNS service. This API uses an asynchronous callback to return the result.
ohos.net.mdns	createDiscoveryService(context: Context, serviceType: string): DiscoveryService	Creates a DiscoveryService object, which is used to discover mDNS services of the specified type.
ohos.net.mdns	resolveLocalService(context: Context, serviceInfo: LocalServiceInfo, callback: AsyncCallback<LocalServiceInfo>): void	Resolves an mDNS service. This API uses an asynchronous callback to return the result.
ohos.net.mdns.DiscoveryService	startSearchingMDNS(): void	Searches for mDNS services on the LAN.
ohos.net.mdns.DiscoveryService	stopSearchingMDNS(): void	Stops searching for mDNS services on the LAN.
ohos.net.mdns.DiscoveryService	on(type: 'discoveryStart', callback: Callback<{serviceInfo: LocalServiceInfo, errorCode?: MdnsError}>): void	Enables listening for discoveryStart events.
ohos.net.mdns.DiscoveryService	off(type: 'discoveryStart', callback?: Callback<{ serviceInfo: LocalServiceInfo, errorCode?: MdnsError }>): void	Disables listening for discoveryStart events.
ohos.net.mdns.DiscoveryService	on(type: 'discoveryStop', callback: Callback<{serviceInfo: LocalServiceInfo, errorCode?: MdnsError}>): void	Enables listening for discoveryStop events.
ohos.net.mdns.DiscoveryService	off(type: 'discoveryStop', callback?: Callback<{ serviceInfo: LocalServiceInfo, errorCode?: MdnsError }>): void	Disables listening for discoveryStop events.
ohos.net.mdns.DiscoveryService	on(type: 'serviceFound', callback: Callback<LocalServiceInfo>): void	Enables listening for serviceFound events.
ohos.net.mdns.DiscoveryService	off(type: 'serviceFound', callback?: Callback<LocalServiceInfo>): void	Disables listening for serviceFound events.
ohos.net.mdns.DiscoveryService	on(type: 'serviceLost', callback: Callback<LocalServiceInfo>): void	Enables listening for serviceLost events.
ohos.net.mdns.DiscoveryService	off(type: 'serviceLost', callback?: Callback<LocalServiceInfo>): void	Disables listening for serviceLost events.

Managing Local Services

Connect the device to the Wi-Fi network.
Import the mdns namespace from @ohos.net.mdns.
Call addLocalService to add a local service.
(Optional) Call resolveLocalService to resolve the local service for the IP address of the local network.
Call removeLocalService to remove the local service.

// Import the mdns namespace from @ohos.net.mdns.
import mdns from '@ohos.net.mdns';
import UIAbility from '@ohos.app.ability.UIAbility';
import { BusinessError } from '@ohos.base';
import featureAbility from '@ohos.ability.featureAbility';
import window from '@ohos.window';

// Construct a singleton object.
export class GlobalContext {
  private constructor() {}
  private static instance: GlobalContext;
  private _objects = new Map<string, Object>();

  public static getContext(): GlobalContext {
    if (!GlobalContext.instance) {
      GlobalContext.instance = new GlobalContext();
    }
    return GlobalContext.instance;
  }

  getObject(value: string): Object|undefined {
    return this._objects.get(value);
  }

  setObject(key: string, objectClass: Object): void {
    this._objects.set(key, objectClass);
  }
}

// Obtain the context of the stage model.
class EntryAbility extends UIAbility {
  value: number = 0;
  onWindowStageCreate(windowStage: window.WindowStage): void{
    GlobalContext.getContext().setObject("value", this.value);
  }
}
let context = GlobalContext.getContext().getObject("value");

class ServiceAttribute {
  key: string = "111"
  value: Array<number> = [1]
}

// Create a LocalService object.
let localServiceInfo: mdns.LocalServiceInfo = {
  serviceType: "_print._tcp",
  serviceName: "servicename",
  port: 5555,
  host: {
    address: "10.14.**.***"
  },
  serviceAttribute: [{key: "111", value: [1]}]
}

// Call addLocalService to add a local service.
mdns.addLocalService(context as Context, localServiceInfo, (error: BusinessError, data: mdns.LocalServiceInfo) =>  {
  console.log(JSON.stringify(error));
  console.log(JSON.stringify(data));
});

// (Optional) Call resolveLocalService to resolve the local service.
mdns.resolveLocalService(context as Context, localServiceInfo, (error: BusinessError, data: mdns.LocalServiceInfo) =>  {
  console.log(JSON.stringify(error));
  console.log(JSON.stringify(data));
});

// Call removeLocalService to remove the local service.
mdns.removeLocalService(context as Context, localServiceInfo, (error: BusinessError, data: mdns.LocalServiceInfo) =>  {
  console.log(JSON.stringify(error));
  console.log(JSON.stringify(data));
});

Discovering Local Services

Connect the device to the Wi-Fi network.
Import the mdns namespace from @ohos.net.mdns.
Create a DiscoveryService object, which is used to discover mDNS services of the specified type.
Subscribe to mDNS service discovery status changes.
Enable discovery of mDNS services on the LAN.
Stop searching for mDNS services on the LAN.
Unsubscribe from mDNS service discovery status changes.

// Import the mdns namespace from @ohos.net.mdns.
import mdns from '@ohos.net.mdns';
import UIAbility from '@ohos.app.ability.UIAbility';
import { BusinessError } from '@ohos.base';
import featureAbility from '@ohos.ability.featureAbility';
import window from '@ohos.window';

// Construct a singleton object.
export class GlobalContext {
  private constructor() {}
  private static instance: GlobalContext;
  private _objects = new Map<string, Object>();

  public static getContext(): GlobalContext {
    if (!GlobalContext.instance) {
      GlobalContext.instance = new GlobalContext();
    }
    return GlobalContext.instance;
  }

  getObject(value: string): Object|undefined {
    return this._objects.get(value);
  }

  setObject(key: string, objectClass: Object): void {
    this._objects.set(key, objectClass);
  }
}

// Obtain the context of the stage model.
class EntryAbility extends UIAbility {
  value:number = 0;
  onWindowStageCreate(windowStage: window.WindowStage): void{
    GlobalContext.getContext().setObject("value", this.value);
  }
}

let context = GlobalContext.getContext().getObject("value");

// Create a DiscoveryService object, which is used to discover mDNS services of the specified type.
let serviceType = "_print._tcp";
let discoveryService = mdns.createDiscoveryService(context as Context, serviceType);

class DataServiceInfo{
  serviceInfo: mdns.LocalServiceInfo|null = null
  errorCode?: mdns.MdnsError = mdns.MdnsError.INTERNAL_ERROR
}
// Subscribe to mDNS service discovery status changes.
discoveryService.on('discoveryStart', (data: DataServiceInfo) => {
  console.log(JSON.stringify(data));
});
discoveryService.on('discoveryStop', (data: DataServiceInfo) => {
  console.log(JSON.stringify(data));
});
discoveryService.on('serviceFound', (data: mdns.LocalServiceInfo) => {
  console.log(JSON.stringify(data));
});
discoveryService.on('serviceLost', (data: mdns.LocalServiceInfo) => {
  console.log(JSON.stringify(data));
});

// Enable discovery of mDNS services on the LAN.
discoveryService.startSearchingMDNS();

// Stop searching for mDNS services on the LAN.
discoveryService.stopSearchingMDNS();

// Unsubscribe from mDNS service discovery status changes.
discoveryService.off('discoveryStart', (data: DataServiceInfo) => {
  console.log(JSON.stringify(data));
});
discoveryService.off('discoveryStop', (data: DataServiceInfo) => {
  console.log(JSON.stringify(data));
});
discoveryService.off('serviceFound', (data: mdns.LocalServiceInfo) => {
  console.log(JSON.stringify(data));
});
discoveryService.off('serviceLost', (data: mdns.LocalServiceInfo) => {
  console.log(JSON.stringify(data));
});