src/android/net/util/NetworkStackUtils.java - platform/packages/modules/NetworkStack - Git at Google

 /*
  * Copyright (C) 2019 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.util;

 import android.content.Context;
 import android.content.pm.PackageManager.NameNotFoundException;
 import android.provider.DeviceConfig;
 import android.util.Log;
 import android.util.SparseArray;

 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;

 import java.io.FileDescriptor;
 import java.io.IOException;
 import java.net.Inet4Address;
 import java.net.Inet6Address;
 import java.net.InetAddress;
 import java.net.SocketException;
 import java.util.List;
 import java.util.function.Predicate;

 /**
  * Collection of utilities for the network stack.
  */
 public class NetworkStackUtils {
     private static final String TAG = "NetworkStackUtils";

     /**
      * A list of captive portal detection specifications used in addition to the fallback URLs.
      * Each spec has the format url@@/@@statusCodeRegex@@/@@contentRegex. Specs are separated
      * by "@@,@@".
      */
     public static final String CAPTIVE_PORTAL_FALLBACK_PROBE_SPECS =
             "captive_portal_fallback_probe_specs";

     /**
      * A comma separated list of URLs used for captive portal detection in addition to the
      * fallback HTTP url associated with the CAPTIVE_PORTAL_FALLBACK_URL settings.
      */
     public static final String CAPTIVE_PORTAL_OTHER_FALLBACK_URLS =
             "captive_portal_other_fallback_urls";

     /**
      * A comma separated list of URLs used for captive portal detection in addition to the HTTP url
      * associated with the CAPTIVE_PORTAL_HTTP_URL settings.
      */
     public static final String CAPTIVE_PORTAL_OTHER_HTTP_URLS = "captive_portal_other_http_urls";

     /**
      * A comma separated list of URLs used for network validation. in addition to the HTTPS url
      * associated with the CAPTIVE_PORTAL_HTTPS_URL settings.
      */
     public static final String CAPTIVE_PORTAL_OTHER_HTTPS_URLS = "captive_portal_other_https_urls";

     /**
      * Which User-Agent string to use in the header of the captive portal detection probes.
      * The User-Agent field is unset when this setting has no value (HttpUrlConnection default).
      */
     public static final String CAPTIVE_PORTAL_USER_AGENT = "captive_portal_user_agent";

     /**
      * Whether to use HTTPS for network validation. This is enabled by default and the setting
      * needs to be set to 0 to disable it. This setting is a misnomer because captive portals
      * don't actually use HTTPS, but it's consistent with the other settings.
      */
     public static final String CAPTIVE_PORTAL_USE_HTTPS = "captive_portal_use_https";

     /**
      * The URL used for HTTPS captive portal detection upon a new connection.
      * A 204 response code from the server is used for validation.
      */
     public static final String CAPTIVE_PORTAL_HTTPS_URL = "captive_portal_https_url";

     /**
      * The URL used for HTTP captive portal detection upon a new connection.
      * A 204 response code from the server is used for validation.
      */
     public static final String CAPTIVE_PORTAL_HTTP_URL = "captive_portal_http_url";

     /**
      * A test URL used to override configuration settings and overlays for the network validation
      * HTTPS URL, when set in {@link android.provider.DeviceConfig} configuration.
      *
      * <p>This URL will be ignored if the host is not "localhost" (it can only be used to test with
      * a local test server), and must not be set in production scenarios (as enforced by CTS tests).
      *
      * <p>{@link #TEST_URL_EXPIRATION_TIME} must also be set to use this setting.
      */
     public static final String TEST_CAPTIVE_PORTAL_HTTPS_URL = "test_captive_portal_https_url";

     /**
      * A test URL used to override configuration settings and overlays for the network validation
      * HTTP URL, when set in {@link android.provider.DeviceConfig} configuration.
      *
      * <p>This URL will be ignored if the host is not "localhost" (it can only be used to test with
      * a local test server), and must not be set in production scenarios (as enforced by CTS tests).
      *
      * <p>{@link #TEST_URL_EXPIRATION_TIME} must also be set to use this setting.
      */
     public static final String TEST_CAPTIVE_PORTAL_HTTP_URL = "test_captive_portal_http_url";

     /**
      * Expiration time of the test URL, in ms, relative to {@link System#currentTimeMillis()}.
      *
      * <p>After this expiration time, test URLs will be ignored. They will also be ignored if
      * the expiration time is more than 10 minutes in the future, to avoid misconfiguration
      * following test runs.
      */
     public static final String TEST_URL_EXPIRATION_TIME = "test_url_expiration_time";

     /**
      * The URL used for fallback HTTP captive portal detection when previous HTTP
      * and HTTPS captive portal detection attemps did not return a conclusive answer.
      */
     public static final String CAPTIVE_PORTAL_FALLBACK_URL = "captive_portal_fallback_url";

     /**
      * What to do when connecting a network that presents a captive portal.
      * Must be one of the CAPTIVE_PORTAL_MODE_* constants above.
      *
      * The default for this setting is CAPTIVE_PORTAL_MODE_PROMPT.
      */
     public static final String CAPTIVE_PORTAL_MODE = "captive_portal_mode";

     /**
      * Don't attempt to detect captive portals.
      */
     public static final int CAPTIVE_PORTAL_MODE_IGNORE = 0;

     /**
      * When detecting a captive portal, display a notification that
      * prompts the user to sign in.
      */
     public static final int CAPTIVE_PORTAL_MODE_PROMPT = 1;

     /**
      * When detecting a captive portal, immediately disconnect from the
      * network and do not reconnect to that network in the future.
      */
     public static final int CAPTIVE_PORTAL_MODE_AVOID = 2;

     /**
      * DNS probe timeout for network validation. Enough for 3 DNS queries 5 seconds apart.
      */
     public static final int DEFAULT_CAPTIVE_PORTAL_DNS_PROBE_TIMEOUT = 12500;

     /**
      * List of fallback probe specs to use for detecting captive portals. This is an alternative to
      * fallback URLs that provides more flexibility on detection rules. Empty, so unused by default.
      */
     public static final String[] DEFAULT_CAPTIVE_PORTAL_FALLBACK_PROBE_SPECS =
             new String[] {};

     /**
      * The default list of HTTP URLs to use for detecting captive portals.
      */
     public static final String[] DEFAULT_CAPTIVE_PORTAL_HTTP_URLS =
             new String [] {"http://connectivitycheck.gstatic.com/generate_204"};

     /**
      * The default list of HTTPS URLs for network validation, to use for confirming internet
      * connectivity.
      */
     public static final String[] DEFAULT_CAPTIVE_PORTAL_HTTPS_URLS =
             new String [] {"https://www.google.com/generate_204"};

     /**
      * @deprecated Considering boolean experiment flag is likely to cause misconfiguration
      *             particularly when NetworkStack module rolls back to previous version. It's
      *             much safer to determine whether or not to enable one specific experimental
      *             feature by comparing flag version with module version.
      */
     @Deprecated
     public static final String DHCP_INIT_REBOOT_ENABLED = "dhcp_init_reboot_enabled";

     /**
      * @deprecated See above explanation.
      */
     @Deprecated
     public static final String DHCP_RAPID_COMMIT_ENABLED = "dhcp_rapid_commit_enabled";

     /**
      * Minimum module version at which to enable the DHCP INIT-REBOOT state.
      */
     public static final String DHCP_INIT_REBOOT_VERSION = "dhcp_init_reboot_version";

     /**
      * Minimum module version at which to enable the DHCP Rapid Commit option.
      */
     public static final String DHCP_RAPID_COMMIT_VERSION = "dhcp_rapid_commit_version";

     /**
      * Minimum module version at which to enable the IP address conflict detection feature.
      */
     public static final String DHCP_IP_CONFLICT_DETECT_VERSION = "dhcp_ip_conflict_detect_version";

     /**
      * Minimum module version at which to enable dismissal CaptivePortalLogin app in validated
      * network feature. CaptivePortalLogin app will also use validation facilities in
      * {@link NetworkMonitor} to perform portal validation if feature is enabled.
      */
     public static final String DISMISS_PORTAL_IN_VALIDATED_NETWORK =
             "dismiss_portal_in_validated_network";

     /**
      * Experiment flag to enable considering DNS probes returning private IP addresses as failed
      * when attempting to detect captive portals.
      *
      * This flag is enabled if !=0 and less than the module APK version.
      */
     public static final String DNS_PROBE_PRIVATE_IP_NO_INTERNET_VERSION =
             "dns_probe_private_ip_no_internet";

     static {
         System.loadLibrary("networkstackutilsjni");
     }

     /**
      * @return True if the array is null or 0-length.
      */
     public static <T> boolean isEmpty(T[] array) {
         return array == null || array.length == 0;
     }

     /**
      * Close a socket, ignoring any exception while closing.
      */
     public static void closeSocketQuietly(FileDescriptor fd) {
         try {
             SocketUtils.closeSocket(fd);
         } catch (IOException ignored) {
         }
     }

     /**
      * Returns an int array from the given Integer list.
      */
     public static int[] convertToIntArray(@NonNull List<Integer> list) {
         int[] array = new int[list.size()];
         for (int i = 0; i < list.size(); i++) {
             array[i] = list.get(i);
         }
         return array;
     }

     /**
      * Returns a long array from the given long list.
      */
     public static long[] convertToLongArray(@NonNull List<Long> list) {
         long[] array = new long[list.size()];
         for (int i = 0; i < list.size(); i++) {
             array[i] = list.get(i);
         }
         return array;
     }

     /**
      * @return True if there exists at least one element in the sparse array for which
      * condition {@code predicate}
      */
     public static <T> boolean any(SparseArray<T> array, Predicate<T> predicate) {
         for (int i = 0; i < array.size(); ++i) {
             if (predicate.test(array.valueAt(i))) {
                 return true;
             }
         }
         return false;
     }

     /**
      * Look up the value of a property for a particular namespace from {@link DeviceConfig}.
      * @param namespace The namespace containing the property to look up.
      * @param name The name of the property to look up.
      * @param defaultValue The value to return if the property does not exist or has no valid value.
      * @return the corresponding value, or defaultValue if none exists.
      */
     @Nullable
     public static String getDeviceConfigProperty(@NonNull String namespace, @NonNull String name,
             @Nullable String defaultValue) {
         String value = DeviceConfig.getProperty(namespace, name);
         return value != null ? value : defaultValue;
     }

     /**
      * Look up the value of a property for a particular namespace from {@link DeviceConfig}.
      * @param namespace The namespace containing the property to look up.
      * @param name The name of the property to look up.
      * @param defaultValue The value to return if the property does not exist or its value is null.
      * @return the corresponding value, or defaultValue if none exists.
      */
     public static int getDeviceConfigPropertyInt(@NonNull String namespace, @NonNull String name,
             int defaultValue) {
         String value = getDeviceConfigProperty(namespace, name, null /* defaultValue */);
         try {
             return (value != null) ? Integer.parseInt(value) : defaultValue;
         } catch (NumberFormatException e) {
             return defaultValue;
         }
     }

     /**
      * Look up the value of a property for a particular namespace from {@link DeviceConfig}.
      * @param namespace The namespace containing the property to look up.
      * @param name The name of the property to look up.
      * @param minimumValue The minimum value of a property.
      * @param maximumValue The maximum value of a property.
      * @param defaultValue The value to return if the property does not exist or its value is null.
      * @return the corresponding value, or defaultValue if none exists or the fetched value is
      *         greater than maximumValue.
      */
     public static int getDeviceConfigPropertyInt(@NonNull String namespace, @NonNull String name,
             int minimumValue, int maximumValue, int defaultValue) {
         int value = getDeviceConfigPropertyInt(namespace, name, defaultValue);
         if (value < minimumValue || value > maximumValue) return defaultValue;
         return value;
     }

     /**
      * Look up the value of a property for a particular namespace from {@link DeviceConfig}.
      * @param namespace The namespace containing the property to look up.
      * @param name The name of the property to look up.
      * @param defaultValue The value to return if the property does not exist or its value is null.
      * @return the corresponding value, or defaultValue if none exists.
      */
     public static boolean getDeviceConfigPropertyBoolean(@NonNull String namespace,
             @NonNull String name, boolean defaultValue) {
         String value = getDeviceConfigProperty(namespace, name, null /* defaultValue */);
         return (value != null) ? Boolean.parseBoolean(value) : defaultValue;
     }

     /**
      * Check whether or not one specific experimental feature for a particular namespace from
      * {@link DeviceConfig} is enabled by comparing NetworkStack module version {@link NetworkStack}
      * with current version of property. If this property version is valid, the corresponding
      * experimental feature would be enabled, otherwise disabled.
      * @param context The global context information about an app environment.
      * @param namespace The namespace containing the property to look up.
      * @param name The name of the property to look up.
      * @return true if this feature is enabled, or false if disabled.
      */
     public static boolean isFeatureEnabled(@NonNull Context context, @NonNull String namespace,
             @NonNull String name) {
         return isFeatureEnabled(context, namespace, name, false /* defaultEnabled */);
     }

     /**
      * Check whether or not one specific experimental feature for a particular namespace from
      * {@link DeviceConfig} is enabled by comparing NetworkStack module version {@link NetworkStack}
      * with current version of property. If this property version is valid, the corresponding
      * experimental feature would be enabled, otherwise disabled.
      * @param context The global context information about an app environment.
      * @param namespace The namespace containing the property to look up.
      * @param name The name of the property to look up.
      * @param defaultEnabled The value to return if the property does not exist or its value is
      *                       null.
      * @return true if this feature is enabled, or false if disabled.
      */
     public static boolean isFeatureEnabled(@NonNull Context context, @NonNull String namespace,
             @NonNull String name, boolean defaultEnabled) {
         try {
             final int propertyVersion = getDeviceConfigPropertyInt(namespace, name,
                     0 /* default value */);
             final long packageVersion = context.getPackageManager().getPackageInfo(
                     context.getPackageName(), 0).getLongVersionCode();
             return (propertyVersion == 0 && defaultEnabled)
                     || (propertyVersion != 0 && packageVersion >= (long) propertyVersion);
         } catch (NameNotFoundException e) {
             Log.e(TAG, "Could not find the package name", e);
             return false;
         }
     }

     /**
      * Attaches a socket filter that accepts DHCP packets to the given socket.
      */
     public static native void attachDhcpFilter(FileDescriptor fd) throws SocketException;

     /**
      * Attaches a socket filter that accepts ICMPv6 router advertisements to the given socket.
      * @param fd the socket's {@link FileDescriptor}.
      * @param packetType the hardware address type, one of ARPHRD_*.
      */
     public static native void attachRaFilter(FileDescriptor fd, int packetType)
             throws SocketException;

     /**
      * Attaches a socket filter that accepts L2-L4 signaling traffic required for IP connectivity.
      *
      * This includes: all ARP, ICMPv6 RS/RA/NS/NA messages, and DHCPv4 exchanges.
      *
      * @param fd the socket's {@link FileDescriptor}.
      * @param packetType the hardware address type, one of ARPHRD_*.
      */
     public static native void attachControlPacketFilter(FileDescriptor fd, int packetType)
             throws SocketException;

     /**
      * Add an entry into the ARP cache.
      */
     public static void addArpEntry(Inet4Address ipv4Addr, android.net.MacAddress ethAddr,
             String ifname, FileDescriptor fd) throws IOException {
         addArpEntry(ethAddr.toByteArray(), ipv4Addr.getAddress(), ifname, fd);
     }

     private static native void addArpEntry(byte[] ethAddr, byte[] netAddr, String ifname,
             FileDescriptor fd) throws IOException;

     /**
      * Return IP address and port in a string format.
      */
     public static String addressAndPortToString(InetAddress address, int port) {
         return String.format(
                 (address instanceof Inet6Address) ? "[%s]:%d" : "%s:%d",
                         address.getHostAddress(), port);
     }

     /**
      * Return true if the provided address is non-null and an IPv6 Unique Local Address (RFC4193).
      */
     public static boolean isIPv6ULA(@Nullable InetAddress addr) {
         return addr instanceof Inet6Address
                 && ((addr.getAddress()[0] & 0xfe) == 0xfc);
     }

     /**
      * Returns the {@code int} nearest in value to {@code value}.
      *
      * @param value any {@code long} value
      * @return the same value cast to {@code int} if it is in the range of the {@code int}
      * type, {@link Integer#MAX_VALUE} if it is too large, or {@link Integer#MIN_VALUE} if
      * it is too small
      */
     public static int saturatedCast(long value) {
         if (value > Integer.MAX_VALUE) {
             return Integer.MAX_VALUE;
         }
         if (value < Integer.MIN_VALUE) {
             return Integer.MIN_VALUE;
         }
         return (int) value;
     }
 }
	/*
	* Copyright (C) 2019 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.util;

	import android.content.Context;
	import android.content.pm.PackageManager.NameNotFoundException;
	import android.provider.DeviceConfig;
	import android.util.Log;
	import android.util.SparseArray;

	import androidx.annotation.NonNull;
	import androidx.annotation.Nullable;

	import java.io.FileDescriptor;
	import java.io.IOException;
	import java.net.Inet4Address;
	import java.net.Inet6Address;
	import java.net.InetAddress;
	import java.net.SocketException;
	import java.util.List;
	import java.util.function.Predicate;

	/**
	* Collection of utilities for the network stack.
	*/
	public class NetworkStackUtils {
	private static final String TAG = "NetworkStackUtils";

	/**
	* A list of captive portal detection specifications used in addition to the fallback URLs.
	* Each spec has the format url@@/@@statusCodeRegex@@/@@contentRegex. Specs are separated
	* by "@@,@@".
	*/
	public static final String CAPTIVE_PORTAL_FALLBACK_PROBE_SPECS =
	"captive_portal_fallback_probe_specs";

	/**
	* A comma separated list of URLs used for captive portal detection in addition to the
	* fallback HTTP url associated with the CAPTIVE_PORTAL_FALLBACK_URL settings.
	*/
	public static final String CAPTIVE_PORTAL_OTHER_FALLBACK_URLS =
	"captive_portal_other_fallback_urls";

	/**
	* A comma separated list of URLs used for captive portal detection in addition to the HTTP url
	* associated with the CAPTIVE_PORTAL_HTTP_URL settings.
	*/
	public static final String CAPTIVE_PORTAL_OTHER_HTTP_URLS = "captive_portal_other_http_urls";

	/**
	* A comma separated list of URLs used for network validation. in addition to the HTTPS url
	* associated with the CAPTIVE_PORTAL_HTTPS_URL settings.
	*/
	public static final String CAPTIVE_PORTAL_OTHER_HTTPS_URLS = "captive_portal_other_https_urls";

	/**
	* Which User-Agent string to use in the header of the captive portal detection probes.
	* The User-Agent field is unset when this setting has no value (HttpUrlConnection default).
	*/
	public static final String CAPTIVE_PORTAL_USER_AGENT = "captive_portal_user_agent";

	/**
	* Whether to use HTTPS for network validation. This is enabled by default and the setting
	* needs to be set to 0 to disable it. This setting is a misnomer because captive portals
	* don't actually use HTTPS, but it's consistent with the other settings.
	*/
	public static final String CAPTIVE_PORTAL_USE_HTTPS = "captive_portal_use_https";

	/**
	* The URL used for HTTPS captive portal detection upon a new connection.
	* A 204 response code from the server is used for validation.
	*/
	public static final String CAPTIVE_PORTAL_HTTPS_URL = "captive_portal_https_url";

	/**
	* The URL used for HTTP captive portal detection upon a new connection.
	* A 204 response code from the server is used for validation.
	*/
	public static final String CAPTIVE_PORTAL_HTTP_URL = "captive_portal_http_url";

	/**
	* A test URL used to override configuration settings and overlays for the network validation
	* HTTPS URL, when set in {@link android.provider.DeviceConfig} configuration.
	*
	* <p>This URL will be ignored if the host is not "localhost" (it can only be used to test with
	* a local test server), and must not be set in production scenarios (as enforced by CTS tests).
	*
	* <p>{@link #TEST_URL_EXPIRATION_TIME} must also be set to use this setting.
	*/
	public static final String TEST_CAPTIVE_PORTAL_HTTPS_URL = "test_captive_portal_https_url";

	/**
	* A test URL used to override configuration settings and overlays for the network validation
	* HTTP URL, when set in {@link android.provider.DeviceConfig} configuration.
	*
	* <p>This URL will be ignored if the host is not "localhost" (it can only be used to test with
	* a local test server), and must not be set in production scenarios (as enforced by CTS tests).
	*
	* <p>{@link #TEST_URL_EXPIRATION_TIME} must also be set to use this setting.
	*/
	public static final String TEST_CAPTIVE_PORTAL_HTTP_URL = "test_captive_portal_http_url";

	/**
	* Expiration time of the test URL, in ms, relative to {@link System#currentTimeMillis()}.
	*
	* <p>After this expiration time, test URLs will be ignored. They will also be ignored if
	* the expiration time is more than 10 minutes in the future, to avoid misconfiguration
	* following test runs.
	*/
	public static final String TEST_URL_EXPIRATION_TIME = "test_url_expiration_time";

	/**
	* The URL used for fallback HTTP captive portal detection when previous HTTP
	* and HTTPS captive portal detection attemps did not return a conclusive answer.
	*/
	public static final String CAPTIVE_PORTAL_FALLBACK_URL = "captive_portal_fallback_url";

	/**
	* What to do when connecting a network that presents a captive portal.
	* Must be one of the CAPTIVE_PORTAL_MODE_* constants above.
	*
	* The default for this setting is CAPTIVE_PORTAL_MODE_PROMPT.
	*/
	public static final String CAPTIVE_PORTAL_MODE = "captive_portal_mode";

	/**
	* Don't attempt to detect captive portals.
	*/
	public static final int CAPTIVE_PORTAL_MODE_IGNORE = 0;

	/**
	* When detecting a captive portal, display a notification that
	* prompts the user to sign in.
	*/
	public static final int CAPTIVE_PORTAL_MODE_PROMPT = 1;

	/**
	* When detecting a captive portal, immediately disconnect from the
	* network and do not reconnect to that network in the future.
	*/
	public static final int CAPTIVE_PORTAL_MODE_AVOID = 2;

	/**
	* DNS probe timeout for network validation. Enough for 3 DNS queries 5 seconds apart.
	*/
	public static final int DEFAULT_CAPTIVE_PORTAL_DNS_PROBE_TIMEOUT = 12500;

	/**
	* List of fallback probe specs to use for detecting captive portals. This is an alternative to
	* fallback URLs that provides more flexibility on detection rules. Empty, so unused by default.
	*/
	public static final String[] DEFAULT_CAPTIVE_PORTAL_FALLBACK_PROBE_SPECS =
	new String[] {};

	/**
	* The default list of HTTP URLs to use for detecting captive portals.
	*/
	public static final String[] DEFAULT_CAPTIVE_PORTAL_HTTP_URLS =
	new String [] {"http://connectivitycheck.gstatic.com/generate_204"};

	/**
	* The default list of HTTPS URLs for network validation, to use for confirming internet
	* connectivity.
	*/
	public static final String[] DEFAULT_CAPTIVE_PORTAL_HTTPS_URLS =
	new String [] {"https://www.google.com/generate_204"};

	/**
	* @deprecated Considering boolean experiment flag is likely to cause misconfiguration
	* particularly when NetworkStack module rolls back to previous version. It's
	* much safer to determine whether or not to enable one specific experimental
	* feature by comparing flag version with module version.
	*/
	@Deprecated
	public static final String DHCP_INIT_REBOOT_ENABLED = "dhcp_init_reboot_enabled";

	/**
	* @deprecated See above explanation.
	*/
	@Deprecated
	public static final String DHCP_RAPID_COMMIT_ENABLED = "dhcp_rapid_commit_enabled";

	/**
	* Minimum module version at which to enable the DHCP INIT-REBOOT state.
	*/
	public static final String DHCP_INIT_REBOOT_VERSION = "dhcp_init_reboot_version";

	/**
	* Minimum module version at which to enable the DHCP Rapid Commit option.
	*/
	public static final String DHCP_RAPID_COMMIT_VERSION = "dhcp_rapid_commit_version";

	/**
	* Minimum module version at which to enable the IP address conflict detection feature.
	*/
	public static final String DHCP_IP_CONFLICT_DETECT_VERSION = "dhcp_ip_conflict_detect_version";

	/**
	* Minimum module version at which to enable dismissal CaptivePortalLogin app in validated
	* network feature. CaptivePortalLogin app will also use validation facilities in
	* {@link NetworkMonitor} to perform portal validation if feature is enabled.
	*/
	public static final String DISMISS_PORTAL_IN_VALIDATED_NETWORK =
	"dismiss_portal_in_validated_network";

	/**
	* Experiment flag to enable considering DNS probes returning private IP addresses as failed
	* when attempting to detect captive portals.
	*
	* This flag is enabled if !=0 and less than the module APK version.
	*/
	public static final String DNS_PROBE_PRIVATE_IP_NO_INTERNET_VERSION =
	"dns_probe_private_ip_no_internet";

	static {
	System.loadLibrary("networkstackutilsjni");
	}

	/**
	* @return True if the array is null or 0-length.
	*/
	public static <T> boolean isEmpty(T[] array) {
	return array == null \|\| array.length == 0;
	}

	/**
	* Close a socket, ignoring any exception while closing.
	*/
	public static void closeSocketQuietly(FileDescriptor fd) {
	try {
	SocketUtils.closeSocket(fd);
	} catch (IOException ignored) {
	}
	}

	/**
	* Returns an int array from the given Integer list.
	*/
	public static int[] convertToIntArray(@NonNull List<Integer> list) {
	int[] array = new int[list.size()];
	for (int i = 0; i < list.size(); i++) {
	array[i] = list.get(i);
	}
	return array;
	}

	/**
	* Returns a long array from the given long list.
	*/
	public static long[] convertToLongArray(@NonNull List<Long> list) {
	long[] array = new long[list.size()];
	for (int i = 0; i < list.size(); i++) {
	array[i] = list.get(i);
	}
	return array;
	}

	/**
	* @return True if there exists at least one element in the sparse array for which
	* condition {@code predicate}
	*/
	public static <T> boolean any(SparseArray<T> array, Predicate<T> predicate) {
	for (int i = 0; i < array.size(); ++i) {
	if (predicate.test(array.valueAt(i))) {
	return true;
	}
	}
	return false;
	}

	/**
	* Look up the value of a property for a particular namespace from {@link DeviceConfig}.
	* @param namespace The namespace containing the property to look up.
	* @param name The name of the property to look up.
	* @param defaultValue The value to return if the property does not exist or has no valid value.
	* @return the corresponding value, or defaultValue if none exists.
	*/
	@Nullable
	public static String getDeviceConfigProperty(@NonNull String namespace, @NonNull String name,
	@Nullable String defaultValue) {
	String value = DeviceConfig.getProperty(namespace, name);
	return value != null ? value : defaultValue;
	}

	/**
	* Look up the value of a property for a particular namespace from {@link DeviceConfig}.
	* @param namespace The namespace containing the property to look up.
	* @param name The name of the property to look up.
	* @param defaultValue The value to return if the property does not exist or its value is null.
	* @return the corresponding value, or defaultValue if none exists.
	*/
	public static int getDeviceConfigPropertyInt(@NonNull String namespace, @NonNull String name,
	int defaultValue) {
	String value = getDeviceConfigProperty(namespace, name, null /* defaultValue */);
	try {
	return (value != null) ? Integer.parseInt(value) : defaultValue;
	} catch (NumberFormatException e) {
	return defaultValue;
	}
	}

	/**
	* Look up the value of a property for a particular namespace from {@link DeviceConfig}.
	* @param namespace The namespace containing the property to look up.
	* @param name The name of the property to look up.
	* @param minimumValue The minimum value of a property.
	* @param maximumValue The maximum value of a property.
	* @param defaultValue The value to return if the property does not exist or its value is null.
	* @return the corresponding value, or defaultValue if none exists or the fetched value is
	* greater than maximumValue.
	*/
	public static int getDeviceConfigPropertyInt(@NonNull String namespace, @NonNull String name,
	int minimumValue, int maximumValue, int defaultValue) {
	int value = getDeviceConfigPropertyInt(namespace, name, defaultValue);
	if (value < minimumValue \|\| value > maximumValue) return defaultValue;
	return value;
	}

	/**
	* Look up the value of a property for a particular namespace from {@link DeviceConfig}.
	* @param namespace The namespace containing the property to look up.
	* @param name The name of the property to look up.
	* @param defaultValue The value to return if the property does not exist or its value is null.
	* @return the corresponding value, or defaultValue if none exists.
	*/
	public static boolean getDeviceConfigPropertyBoolean(@NonNull String namespace,
	@NonNull String name, boolean defaultValue) {
	String value = getDeviceConfigProperty(namespace, name, null /* defaultValue */);
	return (value != null) ? Boolean.parseBoolean(value) : defaultValue;
	}

	/**
	* Check whether or not one specific experimental feature for a particular namespace from
	* {@link DeviceConfig} is enabled by comparing NetworkStack module version {@link NetworkStack}
	* with current version of property. If this property version is valid, the corresponding
	* experimental feature would be enabled, otherwise disabled.
	* @param context The global context information about an app environment.
	* @param namespace The namespace containing the property to look up.
	* @param name The name of the property to look up.
	* @return true if this feature is enabled, or false if disabled.
	*/
	public static boolean isFeatureEnabled(@NonNull Context context, @NonNull String namespace,
	@NonNull String name) {
	return isFeatureEnabled(context, namespace, name, false /* defaultEnabled */);
	}

	/**
	* Check whether or not one specific experimental feature for a particular namespace from
	* {@link DeviceConfig} is enabled by comparing NetworkStack module version {@link NetworkStack}
	* with current version of property. If this property version is valid, the corresponding
	* experimental feature would be enabled, otherwise disabled.
	* @param context The global context information about an app environment.
	* @param namespace The namespace containing the property to look up.
	* @param name The name of the property to look up.
	* @param defaultEnabled The value to return if the property does not exist or its value is
	* null.
	* @return true if this feature is enabled, or false if disabled.
	*/
	public static boolean isFeatureEnabled(@NonNull Context context, @NonNull String namespace,
	@NonNull String name, boolean defaultEnabled) {
	try {
	final int propertyVersion = getDeviceConfigPropertyInt(namespace, name,
	0 /* default value */);
	final long packageVersion = context.getPackageManager().getPackageInfo(
	context.getPackageName(), 0).getLongVersionCode();
	return (propertyVersion == 0 && defaultEnabled)
	\|\| (propertyVersion != 0 && packageVersion >= (long) propertyVersion);
	} catch (NameNotFoundException e) {
	Log.e(TAG, "Could not find the package name", e);
	return false;
	}
	}

	/**
	* Attaches a socket filter that accepts DHCP packets to the given socket.
	*/
	public static native void attachDhcpFilter(FileDescriptor fd) throws SocketException;

	/**
	* Attaches a socket filter that accepts ICMPv6 router advertisements to the given socket.
	* @param fd the socket's {@link FileDescriptor}.
	* @param packetType the hardware address type, one of ARPHRD_*.
	*/
	public static native void attachRaFilter(FileDescriptor fd, int packetType)
	throws SocketException;

	/**
	* Attaches a socket filter that accepts L2-L4 signaling traffic required for IP connectivity.
	*
	* This includes: all ARP, ICMPv6 RS/RA/NS/NA messages, and DHCPv4 exchanges.
	*
	* @param fd the socket's {@link FileDescriptor}.
	* @param packetType the hardware address type, one of ARPHRD_*.
	*/
	public static native void attachControlPacketFilter(FileDescriptor fd, int packetType)
	throws SocketException;

	/**
	* Add an entry into the ARP cache.
	*/
	public static void addArpEntry(Inet4Address ipv4Addr, android.net.MacAddress ethAddr,
	String ifname, FileDescriptor fd) throws IOException {
	addArpEntry(ethAddr.toByteArray(), ipv4Addr.getAddress(), ifname, fd);
	}

	private static native void addArpEntry(byte[] ethAddr, byte[] netAddr, String ifname,
	FileDescriptor fd) throws IOException;

	/**
	* Return IP address and port in a string format.
	*/
	public static String addressAndPortToString(InetAddress address, int port) {
	return String.format(
	(address instanceof Inet6Address) ? "[%s]:%d" : "%s:%d",
	address.getHostAddress(), port);
	}

	/**
	* Return true if the provided address is non-null and an IPv6 Unique Local Address (RFC4193).
	*/
	public static boolean isIPv6ULA(@Nullable InetAddress addr) {
	return addr instanceof Inet6Address
	&& ((addr.getAddress()[0] & 0xfe) == 0xfc);
	}

	/**
	* Returns the {@code int} nearest in value to {@code value}.
	*
	* @param value any {@code long} value
	* @return the same value cast to {@code int} if it is in the range of the {@code int}
	* type, {@link Integer#MAX_VALUE} if it is too large, or {@link Integer#MIN_VALUE} if
	* it is too small
	*/
	public static int saturatedCast(long value) {
	if (value > Integer.MAX_VALUE) {
	return Integer.MAX_VALUE;
	}
	if (value < Integer.MIN_VALUE) {
	return Integer.MIN_VALUE;
	}
	return (int) value;
	}
	}