android-34/android/net/NetworkProvider.java - platform/prebuilts/fullsdk/sources - Git at Google

 /*
  * Copyright (C) 2020 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 package android.net;

 import android.annotation.IntRange;
 import android.annotation.NonNull;
 import android.annotation.Nullable;
 import android.annotation.RequiresPermission;
 import android.annotation.SystemApi;
 import android.content.Context;
 import android.os.Handler;
 import android.os.Looper;
 import android.os.Message;
 import android.os.Messenger;
 import android.util.Log;

 import com.android.internal.annotations.GuardedBy;

 import java.util.ArrayList;
 import java.util.concurrent.Executor;

 /**
  * Base class for network providers such as telephony or Wi-Fi. NetworkProviders connect the device
  * to networks and makes them available to the core network stack by creating
  * {@link NetworkAgent}s. The networks can then provide connectivity to apps and can be interacted
  * with via networking APIs such as {@link ConnectivityManager}.
  *
  * Subclasses should implement {@link #onNetworkRequested} and {@link #onNetworkRequestWithdrawn}
  * to receive {@link NetworkRequest}s sent by the system and by apps. A network that is not the
  * best (highest-scoring) network for any request is generally not used by the system, and torn
  * down.
  *
  * @hide
  */
 @SystemApi
 public class NetworkProvider {
     /**
      * {@code providerId} value that indicates the absence of a provider. It is the providerId of
      * any NetworkProvider that is not currently registered, and of any NetworkRequest that is not
      * currently being satisfied by a network.
      */
     public static final int ID_NONE = -1;

     /**
      * The first providerId value that will be allocated.
      * @hide only used by ConnectivityService.
      */
     public static final int FIRST_PROVIDER_ID = 1;

     /** @hide only used by ConnectivityService */
     public static final int CMD_REQUEST_NETWORK = 1;
     /** @hide only used by ConnectivityService */
     public static final int CMD_CANCEL_REQUEST = 2;

     private final Messenger mMessenger;
     private final String mName;
     private final Context mContext;

     private int mProviderId = ID_NONE;

     /**
      * Constructs a new NetworkProvider.
      *
      * @param looper the Looper on which to run {@link #onNetworkRequested} and
      *               {@link #onNetworkRequestWithdrawn}.
      * @param name the name of the listener, used only for debugging.
      *
      * @hide
      */
     @SystemApi
     public NetworkProvider(@NonNull Context context, @NonNull Looper looper, @NonNull String name) {
         // TODO (b/174636568) : this class should be able to cache an instance of
         // ConnectivityManager so it doesn't have to fetch it again every time.
         final Handler handler = new Handler(looper) {
             @Override
             public void handleMessage(Message m) {
                 switch (m.what) {
                     case CMD_REQUEST_NETWORK:
                         onNetworkRequested((NetworkRequest) m.obj, m.arg1, m.arg2);
                         break;
                     case CMD_CANCEL_REQUEST:
                         onNetworkRequestWithdrawn((NetworkRequest) m.obj);
                         break;
                     default:
                         Log.e(mName, "Unhandled message: " + m.what);
                 }
             }
         };
         mContext = context;
         mMessenger = new Messenger(handler);
         mName = name;
     }

     // TODO: consider adding a register() method so ConnectivityManager does not need to call this.
     /** @hide */
     public @Nullable Messenger getMessenger() {
         return mMessenger;
     }

     /** @hide */
     public @NonNull String getName() {
         return mName;
     }

     /**
      * Returns the ID of this provider. This is known only once the provider is registered via
      * {@link ConnectivityManager#registerNetworkProvider()}, otherwise the ID is {@link #ID_NONE}.
      * This ID must be used when registering any {@link NetworkAgent}s.
      */
     public int getProviderId() {
         return mProviderId;
     }

     /** @hide */
     public void setProviderId(int providerId) {
         mProviderId = providerId;
     }

     /**
      *  Called when a NetworkRequest is received. The request may be a new request or an existing
      *  request with a different score.
      *
      * @param request the NetworkRequest being received
      * @param score the score of the network currently satisfying the request, or 0 if none.
      * @param providerId the ID of the provider that created the network currently satisfying this
      *                   request, or {@link #ID_NONE} if none.
      *
      *  @hide
      */
     @SystemApi
     public void onNetworkRequested(@NonNull NetworkRequest request,
             @IntRange(from = 0, to = 99) int score, int providerId) {}

     /**
      *  Called when a NetworkRequest is withdrawn.
      *  @hide
      */
     @SystemApi
     public void onNetworkRequestWithdrawn(@NonNull NetworkRequest request) {}

     /**
      * Asserts that no provider will ever be able to satisfy the specified request. The provider
      * must only call this method if it knows that it is the only provider on the system capable of
      * satisfying this request, and that the request cannot be satisfied. The application filing the
      * request will receive an {@link NetworkCallback#onUnavailable()} callback.
      *
      * @param request the request that permanently cannot be fulfilled
      * @hide
      */
     @SystemApi
     @RequiresPermission(android.Manifest.permission.NETWORK_FACTORY)
     public void declareNetworkRequestUnfulfillable(@NonNull NetworkRequest request) {
         ConnectivityManager.from(mContext).declareNetworkRequestUnfulfillable(request);
     }

     /**
      * A callback for parties registering a NetworkOffer.
      *
      * This is used with {@link ConnectivityManager#offerNetwork}. When offering a network,
      * the system will use this callback to inform the caller that a network corresponding to
      * this offer is needed or unneeded.
      *
      * @hide
      */
     @SystemApi
     public interface NetworkOfferCallback {
         /**
          * Called by the system when a network for this offer is needed to satisfy some
          * networking request.
          */
         void onNetworkNeeded(@NonNull NetworkRequest request);
         /**
          * Called by the system when this offer is no longer valuable for this request.
          */
         void onNetworkUnneeded(@NonNull NetworkRequest request);
     }

     private class NetworkOfferCallbackProxy extends INetworkOfferCallback.Stub {
         @NonNull public final NetworkOfferCallback callback;
         @NonNull private final Executor mExecutor;

         NetworkOfferCallbackProxy(@NonNull final NetworkOfferCallback callback,
                 @NonNull final Executor executor) {
             this.callback = callback;
             this.mExecutor = executor;
         }

         @Override
         public void onNetworkNeeded(final @NonNull NetworkRequest request) {
             mExecutor.execute(() -> callback.onNetworkNeeded(request));
         }

         @Override
         public void onNetworkUnneeded(final @NonNull NetworkRequest request) {
             mExecutor.execute(() -> callback.onNetworkUnneeded(request));
         }
     }

     @GuardedBy("mProxies")
     @NonNull private final ArrayList<NetworkOfferCallbackProxy> mProxies = new ArrayList<>();

     // Returns the proxy associated with this callback, or null if none.
     @Nullable
     private NetworkOfferCallbackProxy findProxyForCallback(@NonNull final NetworkOfferCallback cb) {
         synchronized (mProxies) {
             for (final NetworkOfferCallbackProxy p : mProxies) {
                 if (p.callback == cb) return p;
             }
         }
         return null;
     }

     /**
      * Register or update an offer for network with the passed capabilities and score.
      *
      * A NetworkProvider's role is to provide networks. This method is how a provider tells the
      * connectivity stack what kind of network it may provide. The score and caps arguments act
      * as filters that the connectivity stack uses to tell when the offer is valuable. When an
      * offer might be preferred over existing networks, the provider will receive a call to
      * the associated callback's {@link NetworkOfferCallback#onNetworkNeeded} method. The provider
      * should then try to bring up this network. When an offer is no longer useful, the stack
      * will inform the provider by calling {@link NetworkOfferCallback#onNetworkUnneeded}. The
      * provider should stop trying to bring up such a network, or disconnect it if it already has
      * one.
      *
      * The stack determines what offers are valuable according to what networks are currently
      * available to the system, and what networking requests are made by applications. If an
      * offer looks like it could connect a better network than any existing network for any
      * particular request, that's when the stack decides the network is needed. If the current
      * networking requests are all satisfied by networks that this offer couldn't possibly be a
      * better match for, that's when the offer is no longer valuable. An offer starts out as
      * unneeded ; the provider should not try to bring up the network until
      * {@link NetworkOfferCallback#onNetworkNeeded} is called.
      *
      * Note that the offers are non-binding to the providers, in particular because providers
      * often don't know if they will be able to bring up such a network at any given time. For
      * example, no wireless network may be in range when the offer would be valuable. This is fine
      * and expected ; the provider should simply continue to try to bring up the network and do so
      * if/when it becomes possible. In the mean time, the stack will continue to satisfy requests
      * with the best network currently available, or if none, keep the apps informed that no
      * network can currently satisfy this request. When/if the provider can bring up the network,
      * the connectivity stack will match it against requests, and inform interested apps of the
      * availability of this network. This may, in turn, render the offer of some other provider
      * low-value if all requests it used to satisfy are now better served by this network.
      *
      * A network can become unneeded for a reason like the above : whether the provider managed
      * to bring up the offered network after it became needed or not, some other provider may
      * bring up a better network than this one, making this network unneeded. A network may also
      * become unneeded if the application making the request withdrew it (for example, after it
      * is done transferring data, or if the user canceled an operation).
      *
      * The capabilities and score act as filters as to what requests the provider will see.
      * They are not promises, but for best performance, the providers should strive to put
      * as much known information as possible in the offer. For the score, it should put as
      * strong a score as the networks will have, since this will filter what requests the
      * provider sees – it's not a promise, it only serves to avoid sending requests that
      * the provider can't ever hope to satisfy better than any current network. For capabilities,
      * it should put all NetworkAgent-managed capabilities a network may have, even if it doesn't
      * have them at first. This applies to INTERNET, for example ; if a provider thinks the
      * network it can bring up for this offer may offer Internet access it should include the
      * INTERNET bit. It's fine if the brought up network ends up not actually having INTERNET.
      *
      * TODO : in the future, to avoid possible infinite loops, there should be constraints on
      * what can be put in capabilities of networks brought up for an offer. If a provider might
      * bring up a network with or without INTERNET, then it should file two offers : this will
      * let it know precisely what networks are needed, so it can avoid bringing up networks that
      * won't actually satisfy requests and remove the risk for bring-up-bring-down loops.
      *
      * @hide
      */
     @SystemApi
     @RequiresPermission(android.Manifest.permission.NETWORK_FACTORY)
     public void registerNetworkOffer(@NonNull final NetworkScore score,
             @NonNull final NetworkCapabilities caps, @NonNull final Executor executor,
             @NonNull final NetworkOfferCallback callback) {
         // Can't offer a network with a provider that is not yet registered or already unregistered.
         final int providerId = mProviderId;
         if (providerId == ID_NONE) return;
         NetworkOfferCallbackProxy proxy = null;
         synchronized (mProxies) {
             for (final NetworkOfferCallbackProxy existingProxy : mProxies) {
                 if (existingProxy.callback == callback) {
                     proxy = existingProxy;
                     break;
                 }
             }
             if (null == proxy) {
                 proxy = new NetworkOfferCallbackProxy(callback, executor);
                 mProxies.add(proxy);
             }
         }
         mContext.getSystemService(ConnectivityManager.class)
                 .offerNetwork(providerId, score, caps, proxy);
     }

     /**
      * Withdraw a network offer previously made to the networking stack.
      *
      * If a provider can no longer provide a network they offered, it should call this method.
      * An example of usage could be if the hardware necessary to bring up the network was turned
      * off in UI by the user. Note that because offers are never binding, the provider might
      * alternatively decide not to withdraw this offer and simply refuse to bring up the network
      * even when it's needed. However, withdrawing the request is slightly more resource-efficient
      * because the networking stack won't have to compare this offer to exiting networks to see
      * if it could beat any of them, and may be advantageous to the provider's implementation that
      * can rely on no longer receiving callbacks for a network that they can't bring up anyways.
      *
      * Warning: This method executes asynchronously. The NetworkOfferCallback object can continue
      * receiving onNetworkNeeded and onNetworkUnneeded callbacks even after this method has
      * returned. In this case, it is on the caller to take appropriate steps in order to prevent
      * bringing up a network.
      *
      * @hide
      */
     @SystemApi
     @RequiresPermission(android.Manifest.permission.NETWORK_FACTORY)
     public void unregisterNetworkOffer(final @NonNull NetworkOfferCallback callback) {
         final NetworkOfferCallbackProxy proxy = findProxyForCallback(callback);
         if (null == proxy) return;
         synchronized (mProxies) {
             mProxies.remove(proxy);
         }
         mContext.getSystemService(ConnectivityManager.class).unofferNetwork(proxy);
     }
 }
	/*
	* Copyright (C) 2020 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	package android.net;

	import android.annotation.IntRange;
	import android.annotation.NonNull;
	import android.annotation.Nullable;
	import android.annotation.RequiresPermission;
	import android.annotation.SystemApi;
	import android.content.Context;
	import android.os.Handler;
	import android.os.Looper;
	import android.os.Message;
	import android.os.Messenger;
	import android.util.Log;

	import com.android.internal.annotations.GuardedBy;

	import java.util.ArrayList;
	import java.util.concurrent.Executor;

	/**
	* Base class for network providers such as telephony or Wi-Fi. NetworkProviders connect the device
	* to networks and makes them available to the core network stack by creating
	* {@link NetworkAgent}s. The networks can then provide connectivity to apps and can be interacted
	* with via networking APIs such as {@link ConnectivityManager}.
	*
	* Subclasses should implement {@link #onNetworkRequested} and {@link #onNetworkRequestWithdrawn}
	* to receive {@link NetworkRequest}s sent by the system and by apps. A network that is not the
	* best (highest-scoring) network for any request is generally not used by the system, and torn
	* down.
	*
	* @hide
	*/
	@SystemApi
	public class NetworkProvider {
	/**
	* {@code providerId} value that indicates the absence of a provider. It is the providerId of
	* any NetworkProvider that is not currently registered, and of any NetworkRequest that is not
	* currently being satisfied by a network.
	*/
	public static final int ID_NONE = -1;

	/**
	* The first providerId value that will be allocated.
	* @hide only used by ConnectivityService.
	*/
	public static final int FIRST_PROVIDER_ID = 1;

	/** @hide only used by ConnectivityService */
	public static final int CMD_REQUEST_NETWORK = 1;
	/** @hide only used by ConnectivityService */
	public static final int CMD_CANCEL_REQUEST = 2;

	private final Messenger mMessenger;
	private final String mName;
	private final Context mContext;

	private int mProviderId = ID_NONE;

	/**
	* Constructs a new NetworkProvider.
	*
	* @param looper the Looper on which to run {@link #onNetworkRequested} and
	* {@link #onNetworkRequestWithdrawn}.
	* @param name the name of the listener, used only for debugging.
	*
	* @hide
	*/
	@SystemApi
	public NetworkProvider(@NonNull Context context, @NonNull Looper looper, @NonNull String name) {
	// TODO (b/174636568) : this class should be able to cache an instance of
	// ConnectivityManager so it doesn't have to fetch it again every time.
	final Handler handler = new Handler(looper) {
	@Override
	public void handleMessage(Message m) {
	switch (m.what) {
	case CMD_REQUEST_NETWORK:
	onNetworkRequested((NetworkRequest) m.obj, m.arg1, m.arg2);
	break;
	case CMD_CANCEL_REQUEST:
	onNetworkRequestWithdrawn((NetworkRequest) m.obj);
	break;
	default:
	Log.e(mName, "Unhandled message: " + m.what);
	}
	}
	};
	mContext = context;
	mMessenger = new Messenger(handler);
	mName = name;
	}

	// TODO: consider adding a register() method so ConnectivityManager does not need to call this.
	/** @hide */
	public @Nullable Messenger getMessenger() {
	return mMessenger;
	}

	/** @hide */
	public @NonNull String getName() {
	return mName;
	}

	/**
	* Returns the ID of this provider. This is known only once the provider is registered via
	* {@link ConnectivityManager#registerNetworkProvider()}, otherwise the ID is {@link #ID_NONE}.
	* This ID must be used when registering any {@link NetworkAgent}s.
	*/
	public int getProviderId() {
	return mProviderId;
	}

	/** @hide */
	public void setProviderId(int providerId) {
	mProviderId = providerId;
	}

	/**
	* Called when a NetworkRequest is received. The request may be a new request or an existing
	* request with a different score.
	*
	* @param request the NetworkRequest being received
	* @param score the score of the network currently satisfying the request, or 0 if none.
	* @param providerId the ID of the provider that created the network currently satisfying this
	* request, or {@link #ID_NONE} if none.
	*
	* @hide
	*/
	@SystemApi
	public void onNetworkRequested(@NonNull NetworkRequest request,
	@IntRange(from = 0, to = 99) int score, int providerId) {}

	/**
	* Called when a NetworkRequest is withdrawn.
	* @hide
	*/
	@SystemApi
	public void onNetworkRequestWithdrawn(@NonNull NetworkRequest request) {}

	/**
	* Asserts that no provider will ever be able to satisfy the specified request. The provider
	* must only call this method if it knows that it is the only provider on the system capable of
	* satisfying this request, and that the request cannot be satisfied. The application filing the
	* request will receive an {@link NetworkCallback#onUnavailable()} callback.
	*
	* @param request the request that permanently cannot be fulfilled
	* @hide
	*/
	@SystemApi
	@RequiresPermission(android.Manifest.permission.NETWORK_FACTORY)
	public void declareNetworkRequestUnfulfillable(@NonNull NetworkRequest request) {
	ConnectivityManager.from(mContext).declareNetworkRequestUnfulfillable(request);
	}

	/**
	* A callback for parties registering a NetworkOffer.
	*
	* This is used with {@link ConnectivityManager#offerNetwork}. When offering a network,
	* the system will use this callback to inform the caller that a network corresponding to
	* this offer is needed or unneeded.
	*
	* @hide
	*/
	@SystemApi
	public interface NetworkOfferCallback {
	/**
	* Called by the system when a network for this offer is needed to satisfy some
	* networking request.
	*/
	void onNetworkNeeded(@NonNull NetworkRequest request);
	/**
	* Called by the system when this offer is no longer valuable for this request.
	*/
	void onNetworkUnneeded(@NonNull NetworkRequest request);
	}

	private class NetworkOfferCallbackProxy extends INetworkOfferCallback.Stub {
	@NonNull public final NetworkOfferCallback callback;
	@NonNull private final Executor mExecutor;

	NetworkOfferCallbackProxy(@NonNull final NetworkOfferCallback callback,
	@NonNull final Executor executor) {
	this.callback = callback;
	this.mExecutor = executor;
	}

	@Override
	public void onNetworkNeeded(final @NonNull NetworkRequest request) {
	mExecutor.execute(() -> callback.onNetworkNeeded(request));
	}

	@Override
	public void onNetworkUnneeded(final @NonNull NetworkRequest request) {
	mExecutor.execute(() -> callback.onNetworkUnneeded(request));
	}
	}

	@GuardedBy("mProxies")
	@NonNull private final ArrayList<NetworkOfferCallbackProxy> mProxies = new ArrayList<>();

	// Returns the proxy associated with this callback, or null if none.
	@Nullable
	private NetworkOfferCallbackProxy findProxyForCallback(@NonNull final NetworkOfferCallback cb) {
	synchronized (mProxies) {
	for (final NetworkOfferCallbackProxy p : mProxies) {
	if (p.callback == cb) return p;
	}
	}
	return null;
	}

	/**
	* Register or update an offer for network with the passed capabilities and score.
	*
	* A NetworkProvider's role is to provide networks. This method is how a provider tells the
	* connectivity stack what kind of network it may provide. The score and caps arguments act
	* as filters that the connectivity stack uses to tell when the offer is valuable. When an
	* offer might be preferred over existing networks, the provider will receive a call to
	* the associated callback's {@link NetworkOfferCallback#onNetworkNeeded} method. The provider
	* should then try to bring up this network. When an offer is no longer useful, the stack
	* will inform the provider by calling {@link NetworkOfferCallback#onNetworkUnneeded}. The
	* provider should stop trying to bring up such a network, or disconnect it if it already has
	* one.
	*
	* The stack determines what offers are valuable according to what networks are currently
	* available to the system, and what networking requests are made by applications. If an
	* offer looks like it could connect a better network than any existing network for any
	* particular request, that's when the stack decides the network is needed. If the current
	* networking requests are all satisfied by networks that this offer couldn't possibly be a
	* better match for, that's when the offer is no longer valuable. An offer starts out as
	* unneeded ; the provider should not try to bring up the network until
	* {@link NetworkOfferCallback#onNetworkNeeded} is called.
	*
	* Note that the offers are non-binding to the providers, in particular because providers
	* often don't know if they will be able to bring up such a network at any given time. For
	* example, no wireless network may be in range when the offer would be valuable. This is fine
	* and expected ; the provider should simply continue to try to bring up the network and do so
	* if/when it becomes possible. In the mean time, the stack will continue to satisfy requests
	* with the best network currently available, or if none, keep the apps informed that no
	* network can currently satisfy this request. When/if the provider can bring up the network,
	* the connectivity stack will match it against requests, and inform interested apps of the
	* availability of this network. This may, in turn, render the offer of some other provider
	* low-value if all requests it used to satisfy are now better served by this network.
	*
	* A network can become unneeded for a reason like the above : whether the provider managed
	* to bring up the offered network after it became needed or not, some other provider may
	* bring up a better network than this one, making this network unneeded. A network may also
	* become unneeded if the application making the request withdrew it (for example, after it
	* is done transferring data, or if the user canceled an operation).
	*
	* The capabilities and score act as filters as to what requests the provider will see.
	* They are not promises, but for best performance, the providers should strive to put
	* as much known information as possible in the offer. For the score, it should put as
	* strong a score as the networks will have, since this will filter what requests the
	* provider sees – it's not a promise, it only serves to avoid sending requests that
	* the provider can't ever hope to satisfy better than any current network. For capabilities,
	* it should put all NetworkAgent-managed capabilities a network may have, even if it doesn't
	* have them at first. This applies to INTERNET, for example ; if a provider thinks the
	* network it can bring up for this offer may offer Internet access it should include the
	* INTERNET bit. It's fine if the brought up network ends up not actually having INTERNET.
	*
	* TODO : in the future, to avoid possible infinite loops, there should be constraints on
	* what can be put in capabilities of networks brought up for an offer. If a provider might
	* bring up a network with or without INTERNET, then it should file two offers : this will
	* let it know precisely what networks are needed, so it can avoid bringing up networks that
	* won't actually satisfy requests and remove the risk for bring-up-bring-down loops.
	*
	* @hide
	*/
	@SystemApi
	@RequiresPermission(android.Manifest.permission.NETWORK_FACTORY)
	public void registerNetworkOffer(@NonNull final NetworkScore score,
	@NonNull final NetworkCapabilities caps, @NonNull final Executor executor,
	@NonNull final NetworkOfferCallback callback) {
	// Can't offer a network with a provider that is not yet registered or already unregistered.
	final int providerId = mProviderId;
	if (providerId == ID_NONE) return;
	NetworkOfferCallbackProxy proxy = null;
	synchronized (mProxies) {
	for (final NetworkOfferCallbackProxy existingProxy : mProxies) {
	if (existingProxy.callback == callback) {
	proxy = existingProxy;
	break;
	}
	}
	if (null == proxy) {
	proxy = new NetworkOfferCallbackProxy(callback, executor);
	mProxies.add(proxy);
	}
	}
	mContext.getSystemService(ConnectivityManager.class)
	.offerNetwork(providerId, score, caps, proxy);
	}

	/**
	* Withdraw a network offer previously made to the networking stack.
	*
	* If a provider can no longer provide a network they offered, it should call this method.
	* An example of usage could be if the hardware necessary to bring up the network was turned
	* off in UI by the user. Note that because offers are never binding, the provider might
	* alternatively decide not to withdraw this offer and simply refuse to bring up the network
	* even when it's needed. However, withdrawing the request is slightly more resource-efficient
	* because the networking stack won't have to compare this offer to exiting networks to see
	* if it could beat any of them, and may be advantageous to the provider's implementation that
	* can rely on no longer receiving callbacks for a network that they can't bring up anyways.
	*
	* Warning: This method executes asynchronously. The NetworkOfferCallback object can continue
	* receiving onNetworkNeeded and onNetworkUnneeded callbacks even after this method has
	* returned. In this case, it is on the caller to take appropriate steps in order to prevent
	* bringing up a network.
	*
	* @hide
	*/
	@SystemApi
	@RequiresPermission(android.Manifest.permission.NETWORK_FACTORY)
	public void unregisterNetworkOffer(final @NonNull NetworkOfferCallback callback) {
	final NetworkOfferCallbackProxy proxy = findProxyForCallback(callback);
	if (null == proxy) return;
	synchronized (mProxies) {
	mProxies.remove(proxy);
	}
	mContext.getSystemService(ConnectivityManager.class).unofferNetwork(proxy);
	}
	}