Add a NetworkProvider class to the SDK.

Bug: 138306002
Test: builds, boots, wifi and telephony work
Test: tested by upcoming change that uses this in NetworkFactory
Change-Id: I2f61bf323215b7c6feff8acc92e7434346751773
diff --git a/core/java/android/net/NetworkProvider.java b/core/java/android/net/NetworkProvider.java
new file mode 100644
index 0000000..2c0e4aa
--- /dev/null
+++ b/core/java/android/net/NetworkProvider.java
@@ -0,0 +1,166 @@
+/*
+ * 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.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;
+
+/**
+ * Base class for network providers such as telephony or Wi-Fi. NetworkProviders connect the device
+ * to networks and makes them available to 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 #onRequestWithdrawn} 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;
+
+    /**
+     * A hardcoded ID for NetworkAgents representing VPNs. These agents are not created by any
+     * provider, so they use this constant for clarity instead of NONE.
+     * @hide only used by ConnectivityService.
+     */
+    public static final int ID_VPN = -2;
+
+    /**
+     * 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 ConnectivityManager mCm;
+
+    private int mProviderId = ID_NONE;
+
+    /**
+     * Constructs a new NetworkProvider.
+     *
+     * @param looper the Looper on which to run {@link #onNetworkRequested} and
+     *               {@link #onRequestWithdrawn}.
+     * @param name the name of the listener, used only for debugging.
+     *
+     * @hide
+     */
+    @SystemApi
+    public NetworkProvider(@NonNull Context context, @NonNull Looper looper, @NonNull String name) {
+        mCm = ConnectivityManager.from(context);
+
+        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:
+                        onRequestWithdrawn((NetworkRequest) m.obj);
+                        break;
+                    default:
+                        Log.e(mName, "Unhandled message: " + m.what);
+                }
+            }
+        };
+        mMessenger = new Messenger(handler);
+        mName = name;
+    }
+
+    // TODO: consider adding a register() method so ConnectivityManager does not need to call this.
+    public @Nullable Messenger getMessenger() {
+        return mMessenger;
+    }
+
+    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, int score, int providerId) {}
+
+    /**
+     *  Called when a NetworkRequest is withdrawn.
+     *  @hide
+     */
+    @SystemApi
+    public void onRequestWithdrawn(@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 cannot be fulfilled
+     * @hide
+     */
+    @SystemApi
+    @RequiresPermission(android.Manifest.permission.NETWORK_FACTORY)
+    public void declareNetworkRequestUnfulfillable(@NonNull NetworkRequest request) {
+        mCm.declareNetworkRequestUnfulfillable(request);
+    }
+}