Improve doc for NetCaps and NetRequest, and add slice XML docs

Test: comment-only change Bug: 266524688 Change-Id: Iffeba94ea8e2f4913188ae33933ef30c532ea13a
2023-02-10 14:01:49 +09:00
parent 09cad2bc2d
commit 82f1b5e818
2 changed files with 158 additions and 15 deletions
--- a/framework/src/android/net/NetworkCapabilities.java
+++ b/framework/src/android/net/NetworkCapabilities.java
@@ -53,18 +53,70 @@ import java.util.Set;
 import java.util.StringJoiner;

 /**
- * Representation of the capabilities of an active network. Instances are
- * typically obtained through
- * {@link NetworkCallback#onCapabilitiesChanged(Network, NetworkCapabilities)}
- * or {@link ConnectivityManager#getNetworkCapabilities(Network)}.
- * <p>
- * This replaces the old {@link ConnectivityManager#TYPE_MOBILE} method of
- * network selection. Rather than indicate a need for Wi-Fi because an
- * application needs high bandwidth and risk obsolescence when a new, fast
- * network appears (like LTE), the application should specify it needs high
- * bandwidth. Similarly if an application needs an unmetered network for a bulk
- * transfer it can specify that rather than assuming all cellular based
- * connections are metered and all Wi-Fi based connections are not.
+ * Representation of the capabilities of an active network.
+ *
+ * <p>@see <a href="https://developer.android.com/training/basics/network-ops/reading-network-state>
+ * this general guide</a> on how to use NetworkCapabilities and related classes.
+ *
+ * <p>NetworkCapabilities represent what a network can do and what its
+ * characteristics are like. The principal attribute of NetworkCapabilities
+ * is in the capabilities bits, which are checked with
+ * {@link #hasCapability(int)}. See the list of capabilities and each
+ * capability for a description of what it means.
+ *
+ * <p>Some prime examples include {@code NET_CAPABILITY_MMS}, which means that the
+ * network is capable of sending MMS. A network without this capability
+ * is not capable of sending MMS.
+ * <p>The {@code NET_CAPABILITY_INTERNET} capability means that the network is
+ * configured to reach the general Internet. It may or may not actually
+ * provide connectivity ; the {@code NET_CAPABILITY_VALIDATED} bit indicates that
+ * the system found actual connectivity to the general Internet the last
+ * time it checked. Apps interested in actual connectivity should usually
+ * look at both these capabilities.
+ * <p>The {@code NET_CAPABILITY_NOT_METERED} capability is set for networks that
+ * do not bill the user for consumption of bytes. Applications are
+ * encouraged to consult this to determine appropriate usage, and to
+ * limit usage of metered network where possible, including deferring
+ * big downloads until such a time that an unmetered network is connected.
+ * Also see {@link android.app.job.JobScheduler} to help with scheduling such
+ * downloads, in particular
+ * {@link android.app.job.JobInfo.Builder#setRequiredNetwork(NetworkRequest)}.
+ * <p>NetworkCapabilities contain a number of other capabilities that
+ * represent what modern networks can and can't do. Look up the individual
+ * capabilities in this class to learn about each of them.
+ *
+ * <p>NetworkCapabilities typically represent attributes that can apply to
+ * any network. The attributes that apply only to specific transports like
+ * cellular or Wi-Fi can be found in the specifier (for requestable attributes)
+ * or in the transport info (for non-requestable ones). See
+ * {@link #getNetworkSpecifier} and {@link #getTransportInfo}. An app would
+ * downcast these to the specific class for the transport they need if they
+ * are interested in transport-specific attributes. Also see
+ * {@link android.net.wifi.WifiNetworkSpecifier} or
+ * {@link android.net.wifi.WifiInfo} for some examples of each of these.
+ *
+ * <p>NetworkCapabilities also contains other attributes like the estimated
+ * upstream and downstream bandwidth and the specific transport of that
+ * network (e.g. {@link #TRANSPORT_CELLULAR}). Generally, apps should normally
+ * have little reason to check for the type of transport ; for example, to
+ * query whether a network costs money to the user, do not look at the
+ * transport, but instead look at the absence or presence of
+ * {@link #NET_CAPABILITY_NOT_METERED} which will correctly account for
+ * metered Wi-Fis and free of charge cell connections.
+ *
+ * <p>The system communicates with apps about connected networks and uses
+ * NetworkCapabilities to express these capabilities about these networks.
+ * Apps should register callbacks with the {@link ConnectivityManager#requestNetwork}
+ * or {@link ConnectivityManager#registerNetworkCallback} family of methods
+ * to learn about the capabilities of a network on a continuous basis
+ * and be able to react to changes to capabilities. For quick debugging Android also
+ * provides {@link ConnectivityManager#getNetworkCapabilities(Network)},
+ * but the dynamic nature of networking makes this ill-suited to production
+ * code since capabilities obtained in this way can go stale immediately.
+ *
+ * <p>Also see {@link NetworkRequest} which uses the same capabilities
+ * together with {@link ConnectivityManager#requestNetwork} for how to
+ * request the system brings up the kind of network your application needs.
 */
 public final class NetworkCapabilities implements Parcelable {
    private static final String TAG = "NetworkCapabilities";
@@ -622,11 +674,19 @@ public final class NetworkCapabilities implements Parcelable {

    /**
     * Indicates that this network should be able to prioritize latency for the internet.
+     *
+     * Starting with {@link Build.VERSION_CODES#UPSIDE_DOWN_CAKE}, requesting this capability with
+     * {@link ConnectivityManager#requestNetwork} requires declaration in the self-certified
+     * network capabilities. See {@link NetworkRequest} for the self-certification documentation.
     */
    public static final int NET_CAPABILITY_PRIORITIZE_LATENCY = 34;

    /**
     * Indicates that this network should be able to prioritize bandwidth for the internet.
+     *
+     * Starting with {@link Build.VERSION_CODES#UPSIDE_DOWN_CAKE}, requesting this capability with
+     * {@link ConnectivityManager#requestNetwork} requires declaration in the self-certified
+     * network capabilities. See {@link NetworkRequest} for the self-certification documentation.
     */
    public static final int NET_CAPABILITY_PRIORITIZE_BANDWIDTH = 35;

--- a/framework/src/android/net/NetworkRequest.java
+++ b/framework/src/android/net/NetworkRequest.java
@@ -54,9 +54,92 @@ import java.util.Objects;
 import java.util.Set;

 /**
- * Defines a request for a network, made through {@link NetworkRequest.Builder} and used
- * to request a network via {@link ConnectivityManager#requestNetwork} or listen for changes
- * via {@link ConnectivityManager#registerNetworkCallback}.
+ * An object describing a network that the application is interested in.
+ *
+ * <p>@see <a href="https://developer.android.com/training/basics/network-ops/reading-network-state>
+ * this general guide</a> on how to use NetworkCapabilities and related classes.
+ *
+ * NetworkRequest defines a request for a network, made through
+ * {@link NetworkRequest.Builder} and used to request a network via
+ * {@link ConnectivityManager#requestNetwork} or to listen for changes
+ * via the {@link ConnectivityManager#registerNetworkCallback} family of
+ * functions.
+ *
+ * <p>{@link ConnectivityManager#requestNetwork} will try to find a connected
+ * network matching the NetworkRequest, and return it if there is one.
+ * As long as the request is outstanding, the system will try to find the best
+ * possible network that matches the request. The request will keep up the
+ * currently best connected network, and if a better one is found (e.g. cheaper
+ * or faster) the system will bring up that better network to better serve the
+ * request. A request filed with {@link ConnectivityManager#requestNetwork} will
+ * only match one network at a time (the one the system thinks is best), even if
+ * other networks can match the request that are being kept up by other requests.
+ *
+ * For example, an application needing a network with
+ * {@link NetworkCapabilities#NET_CAPABILITY_INTERNET} should use
+ * {@link ConnectivityManager#requestNetwork} to request the system keeps one up.
+ * A general cellular network can satisfy this request, but if the system finds
+ * a free Wi-Fi network which is expected to be faster, it will try and connect
+ * to that Wi-Fi network and switch the request over to it once it is connected.
+ * The cell network may stay connected if there are outstanding requests (from
+ * the same app or from other apps on the system) that match the cell network
+ * but not the Wi-Fi network, such as a request with {@link NetworkCapabilities#NET_CAPABILITY_MMS}.
+ *
+ * When a network is no longer needed to serve any request, the system can
+ * tear it down at any time and usually does so immediately, so make sure to
+ * keep up requests for the networks your app needs.
+ *
+ * <p>By contrast, requests filed with {@link ConnectivityManager#registerNetworkCallback}
+ * will receive callbacks for all matching networks, and will not cause the system to
+ * keep up the networks they match. Use this to listen to networks that the device is
+ * connected to, but that you don't want the system to keep up for your use case.
+ *
+ * <p>Applications build a NetworkRequest and pass it to one of the
+ * {@link ConnectivityManager} methods above together with a
+ * {@link ConnectivityManager.NetworkCallback} object. The callback
+ * will then start receiving method calls about networks that match
+ * the request.
+ *
+ * <p>Networks are brought up and/or matched according to the capabilities
+ * set in the builder. For example, a request with
+ * {@link NetworkCapabilities#NET_CAPABILITY_MMS} lets the system match
+ * and/or bring up a network that is capable to send MMS. A request with
+ * {@link NetworkCapabilities#NET_CAPABILITY_NOT_METERED} matches a network
+ * that doesn't charge the user for usage. See
+ * {@link NetworkCapabilities} for a list of capabilities and their
+ * description.
+ *
+ * <p>While all capabilities can be matched with the
+ * {@link ConnectivityManager#registerNetworkCallback} family of methods,
+ * not all capabilities can be used to request that the system brings
+ * up a network with {@link ConnectivityManager#requestNetwork}. For example,
+ * an application cannot use {@link ConnectivityManager#requestNetwork} to
+ * ask the system to bring up a network with
+ * {@link NetworkCapabilities#NET_CAPABILITY_CAPTIVE_PORTAL}, because the
+ * system won't know if a network has a captive portal before it connects
+ * to that network. Similarly, some capabilities may require a specific
+ * permission or privilege to be requested.
+ *
+ * Look up the specific capability and the {@link ConnectivityManager#requestNetwork}
+ * method for limitations applicable to each capability.
+ *
+ * <p>Also, starting with {@link Build.VERSION_CODES#UPSIDE_DOWN_CAKE}, some capabilities
+ * require the application to self-certify by explicitly adding the
+ * {@link android.content.pm.PackageManager#PROPERTY_SELF_CERTIFIED_NETWORK_CAPABILITIES}
+ * property in the AndroidManifest.xml, which points to an XML resource file. In the
+ * XML resource file, the application declares what kind of network capabilities the application
+ * wants to have.
+ *
+ * Here is an example self-certification XML resource file :
+ * <pre>
+ *  {@code
+ *  <network-capabilities-declaration xmlns:android="http://schemas.android.com/apk/res/android">
+ *     <uses-network-capability android:name="NET_CAPABILITY_PRIORITIZE_LATENCY"/>
+ *     <uses-network-capability android:name="NET_CAPABILITY_PRIORITIZE_BANDWIDTH"/>
+ * </network-capabilities-declaration>
+ *  }
+ *  </pre>
+ * Look up the specific capability to learn whether its usage requires this self-certification.
 */
 public class NetworkRequest implements Parcelable {
    /**