Develop Reference

Android WifiManager failed when called RemoveNetwork()

I have implemented an app which will allow user to connect to a desired network.
If the SSID record is already remembered by phone. It will notify user to manually delete the SSID record.
Here is some sample code
temp = -1;
for (int i = 0; i < WiFi.ConfiguredNetworks.Count; i++)
{
if (String.Compare(WiFi.ConfiguredNetworks[i].Ssid, ("\"" + SSID + "\"")) == 0)
{
temp = WiFi.ConfiguredNetworks[i].NetworkId;
break;
}
}
if(temp != -1) //This SSID is already remembered by phone
{
bool success = WiFi.RemoveNetwork(temp)
if(success == false)
{
//Call some function to notify user to manually remove the network
}
}
Things happened at //Call some function to notify user to manually remove the network.
Sometimes the user goes to the wifi system page. They found out that there is no record of this SSID.
In my opinion, if RemoveNetwork() return failed, that means this SSID is already remembered by phone.
And it is not build by the current app.
Is that wrong?
Issue happened on device Nokia 8(Android 9).

As the docs for WifiManager say:
Compatibility Note: For applications targeting Build.VERSION_CODES.Q or above, this API will always fail and return false.
If your API level is below 29 then you probably aren't passing a valid NetworkId.

Device Owner Admin / DevicePolicyManager, Possible to turn on Mobile Data & Data Roaming automatically on Android?

So I am developing an app which works as device owner on the specific Android device. This app is not available on the play store, but gets transferred with a provisioning app from a different device via NFC. Since those devices will be very specific to certain tasks (scanning NFC tags), I want to enable and disable a few things from the very beginning.
I want to disable sound:
devicePolicyManager.setMasterVolumeMuted(adminComponentName, true);
But this doesn't seem to work at all, but no exception either.
But what I really want to do is enabling mobile Data and Roaming, the SIM cards which we are using support that.
devicePolicyManager.setSecureSetting(adminComponentName, Settings.Global.DATA_ROAMING, String.valueOf(1));
devicePolicyManager.setSecureSetting(adminComponentName,"mobile_data",String.valueOf(1));
But sadly, those two lines of code throw a security exception:
java.lang.SecurityException: Permission denial: Device owners cannot update mobile_data
Interestingly, inserting APNs work (later in the code) Any chance to be able to turn on mobile data and data roaming as a device admin/owner? I mean, thats the whole purpose of being a device admin, right?
Here is the full code for reference: (the parts which make the app crash are commented out)
public static void enableRestrictedAppsAndSettings(Activity activity) {
ComponentName adminComponentName = DeviceAdminReceiver.getComponentName(activity);
DevicePolicyManager devicePolicyManager = (DevicePolicyManager) activity.getSystemService(Context.DEVICE_POLICY_SERVICE);
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
// disable keyguard and sound
devicePolicyManager.setKeyguardDisabled(adminComponentName, true);
devicePolicyManager.setMasterVolumeMuted(adminComponentName, true);
devicePolicyManager.setSecureSetting(adminComponentName, Settings.Secure.LOCATION_MODE, String.valueOf(Settings.Secure.LOCATION_MODE_HIGH_ACCURACY));
//devicePolicyManager.setSecureSetting(adminComponentName, Settings.Global.DATA_ROAMING, String.valueOf(1));
//devicePolicyManager.setSecureSetting(adminComponentName,"mobile_data",String.valueOf(1));
}
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
if (devicePolicyManager.isDeviceOwnerApp(activity.getApplicationContext().getPackageName())) {
devicePolicyManager.enableSystemApp(adminComponentName,"com.sec.android.app.camera");
devicePolicyManager.clearUserRestriction(adminComponentName, UserManager.DISALLOW_DATA_ROAMING);
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.P) {
L.debug("KIOSK", "APN");
ApnSetting apn;
TelephonyManager manager = (TelephonyManager)activity.getSystemService(Context.TELEPHONY_SERVICE);
if (manager.getSimState() == TelephonyManager.SIM_STATE_READY) {
String mcc = manager.getSimOperator().substring(0, 3);
String mnc = manager.getSimOperator().substring(3);
L.debug("KIOSK " + mcc + " "+mnc);
apn = new ApnSetting.Builder()
.setApnTypeBitmask(ApnSetting.TYPE_DEFAULT)
.setApnName("em")
.setEntryName("em")
.setOperatorNumeric(mcc + mnc) // this is a must its consists from Telephony.Carriers.MCC + Telephony.Carriers.MNC, In my case, I had to pad the MNC with a leading zero
.setProtocol(ApnSetting.PROTOCOL_IPV4V6) // this is a must
.setRoamingProtocol(ApnSetting.PROTOCOL_IPV4V6) // this is a must
.setCarrierEnabled(true)
.build();
devicePolicyManager.removeOverrideApn(adminComponentName,0);
devicePolicyManager.addOverrideApn(adminComponentName, apn);
devicePolicyManager.setOverrideApnsEnabled(adminComponentName, true);
}
}
}
}

Unfortunately the device owner has no access to mobile data status (you're right, weird restriction for the device owner app!).
However, you can still get the mobile data status and force the user to turn it on or off if the status is wrong. Here're the code samples (thanks to Test if background data and packet data is enabled or not).
public static boolean isMobileDataEnabled(Context context) {
ConnectivityManager cm = (ConnectivityManager)context.getSystemService(Context.CONNECTIVITY_SERVICE);
try {
Class clazz = Class.forName(cm.getClass().getName());
Method method = clazz.getDeclaredMethod("getMobileDataEnabled");
method.setAccessible(true); // Make the method callable
// get the setting for "mobile data"
return (Boolean) method.invoke(cm);
} catch (Exception e) {
// Let it will be true by default
return true;
}
}
This code works on Android 5-9 (not tested on Android 10 yet).
So you run a background service which performs this check once per some seconds and requires the user to turn on/off the mobile data in the status bar.
You can see how it is done by cloning this open source Android MDM (this is my project). The method is here: Utils.isMobileDataEnabled(Context context).

Android Enterprise - BluetoothAdapter.startDiscovery() does not start scan

I am using BluetoothAdapter.startDiscovery() to find a specific Bluetooth device (it is Bluetooth 2.0 device, so I have to use BluetoothAdapter.startDiscovery()). I have all required permissions (Bluetooth, Location), and the app works just fine.
But now I have to use this app under Android Enterprise (Work Profile). Under Work Profile it does not start scan. All the limitations in the profile are disabled.
After investigation logcat I found such lines:
Non work profile log:
2019-07-29 10:23:13.109 10230-10446/? D/BluetoothAdapterService: startDiscovery() uid = 10126, pid = 6328
2019-07-29 10:23:13.110 10230-10446/? D/BluetoothAdapterService: startDiscovery
Work profile log:
2019-07-29 10:21:26.536 10230-13473/? D/BluetoothAdapterService: startDiscovery() uid = 1010126, pid = 13390
2019-07-29 10:21:26.536 10230-13473/? W/BluetoothAdapterService: startDiscovery() - Not allowed for non-active user
This is the log from OnePlus 6, but I observed similar logcat also on Samsung S10. Also customers said they have same problem on S9, S8 and on some Nokia device (actually all devices they tested on).
Searching through Android sources, I found the following code, producing this log:
public boolean startDiscovery() {
if (!Utils.checkCaller()) {
Log.w(TAG, "startDiscovery() - Not allowed for non-active user");
return false;
}
AdapterService service = getService();
if (service == null) return false;
return service.startDiscovery();
}
Which calls Utils.checkCaller() to check:
public static boolean checkCaller() {
boolean ok;
// Get the caller's user id then clear the calling identity
// which will be restored in the finally clause.
int callingUser = UserHandle.getCallingUserId();
int callingUid = Binder.getCallingUid();
long ident = Binder.clearCallingIdentity();
try {
// With calling identity cleared the current user is the foreground user.
int foregroundUser = ActivityManager.getCurrentUser();
ok = (foregroundUser == callingUser);
if (!ok) {
// Always allow SystemUI/System access.
int systemUiUid = ActivityThread.getPackageManager().getPackageUid(
"com.android.systemui", UserHandle.USER_OWNER);
ok = (systemUiUid == callingUid) || (Process.SYSTEM_UID == callingUid);
}
} catch (Exception ex) {
Log.e(TAG, "checkIfCallerIsSelfOrForegroundUser: Exception ex=" + ex);
ok = false;
} finally {
Binder.restoreCallingIdentity(ident);
}
return ok;
}
So startDiscovery() uid = 10126 and startDiscovery() uid = 1010126 differ in uid, which I think is caused by work profile, which as I think causes the check (foregroundUser == callingUser) to be false.
Finally the question: Am I right that it is a bug? If yes - is there any way to workaround it? If no - how can I enable Bluetooth classic scan in work profile?

How to update an already created Wi-Fi configuration (or "UID XXX does not have permission to update [Wi-Fi] configuration error")?

I am developing an app which manages the Wi-Fi connections. My scenario is as follows: Let's say, the entire building has a Wi-Fi network named “testing-tls”. My app should be able to connect to only selected access points (based on BSSID or MAC ID). We use TLS authentication mechanism to verify the user (Custom CA Certificates).
I am able to establish a connection through the app, but failing when I try to connect to a different access point (different BSSID). Even though I created the Wi-Fi configuration programmatically, I am unable to update configuration after a first successful connection. I have tested my app in Oreo and Marshmallow. But, I am facing problems in Oreo (Not sure about Nougat). I am beginning to wonder if it is even possible to update the configuration once it is created.
These are the steps I am following:
1) Create a WifiConfiguration object
private WifiConfiguration createWifiConfiguration() {
WifiConfiguration config = new WifiConfiguration();
config.SSID = "\"testing-tls\"";
config.priority = 1;
config.status = WifiConfiguration.Status.ENABLED;
config.allowedKeyManagement.set(WifiConfiguration.KeyMgmt.WPA_EAP;
config.allowedKeyManagement.set(WifiConfiguration.KeyMgmt.IEEE8021X);
config.enterpriseConfig.setIdentity(identityName);
config.enterpriseConfig.setEapMethod(WifiEnterpriseConfig.Eap.TLS);
PKCS12ParseInfo parseInfo;
try {
parseInfo = CertificateUtils.parsePKCS12Certificate(
certificateFilePath, identityPassword);
if (parseInfo != null) {
config.enterpriseConfig.setClientKeyEntry(parseInfo.getPrivateKey(),
parseInfo.getCertificate());
return config;
}
return null;
} catch (KeyStoreException | NoSuchAlgorithmException | IOException |
CertificateException | UnrecoverableKeyException | KeyManagementException e1) {
Timber.e("WifiMonitorService, Fail to parse the input certificate: %s", e1.toString());
Toast.makeText(this, "Error occurred", Toast.LENGTH_SHORT).show();
return null;
}
}
2) Try to establish a connection
private void establishWifiConnection(String result) {
Timber.d("WifiMonitorService, establishing WifiConnection");
WifiConfiguration configuration = createWifiConfiguration();
if (configuration != null) {
// result contains a mac id - 00:45:69:c5:34:f2
configuration.BSSID = result;
int networkId = wifiManager.addNetwork(configuration);
if (networkId == -1) {
networkId = getExistingNetworkId(wifiSsid);
// Add a new configuration to the db
if (networkId == -1) {
Timber.e("Couldn't add network with SSID");
Toast.makeText(this, "Wifi configuration error", Toast.LENGTH_SHORT).show();
return;
}
}
Timber.i("WifiMonitorService, # addNetwork returned: %d", networkId);
wifiManager.saveConfiguration();
wifiManager.enableNetwork(networkId, true);
wifiManager.reassociate();
} else {
Toast.makeText(this, "Wifi conf Error occurred", Toast.LENGTH_SHORT).show();
}
}
3) Get Exiting network id if present
private int getExistingNetworkId(String ssid) {
List<WifiConfiguration> configuredNetworks =
wifiManager.getConfiguredNetworks();
if (configuredNetworks != null) {
for (WifiConfiguration existingConfig : configuredNetworks) {
if (existingConfig.SSID.equals("\"testing-tls\"")) {
return existingConfig.networkId;
}
}
}
return -1;
}
Manifest Permissions are as follows:
<uses-permission android:name="android.permission.CAMERA" />
<uses-permission android:name="android.permission.VIBRATE" />
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
<uses-permission android:name="android.permission.CHANGE_WIFI_STATE" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.CHANGE_NETWORK_STATE" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.WAKE_LOCK" />
<uses-permission android:name="android.permission.OVERRIDE_WIFI_CONFIG" />
<uses-permission android:name="android.permission.NETWORK_SETTINGS" />
<uses-feature android:name="android.hardware.wifi" />
<uses-feature android:name="android.hardware.camera" />
<permission
android:name="android.permission.INTERACT_ACROSS_USERS"
android:protectionLevel="signature" />
Error: I always get UID 10189 does not have permission to update configuration error in Oreo
2018-12-28 12:23:44.571 1320-1847/? E/WifiConfigManager: UID 10189 does not have permission to update configuration "testing-tls"WPA_EAP
2018-12-28 12:23:44.571 1320-1847/? I/WifiStateMachine: connectToUserSelectNetwork Allowing uid 10189 with insufficient permissions to connect=1
Investigation
After digging through the source code, I found the implementation of the addOrUpdateNetwork method in WifiConfigManager class.
The implementation addOrUpdateNetwork, in tag android_8.0.0_r21 (Build number OPD1.170816.010) is as follows:
First check if we already have a network with the provided network id or configKey
If no existing network found, validate the configuration, and add.
If existing network found, update the network configuration. Before that, check whether app has necesssary permissions to update the network.
AddOrUpdateNetwork internally calls a function called canModifyNetwork:
/**
* Checks if |uid| has permission to modify the provided configuration.
*
* #param config WifiConfiguration object corresponding to the network to be modified.
* #param uid UID of the app requesting the modification.
* #param ignoreLockdown Ignore the configuration lockdown checks for connection attempts.
*/
private boolean canModifyNetwork(WifiConfiguration config, int uid, boolean ignoreLockdown) {
// Passpoint configurations are generated and managed by PasspointManager. They can be
// added by either PasspointNetworkEvaluator (for auto connection) or Settings app
// (for manual connection), and need to be removed once the connection is completed.
// Since it is "owned" by us, so always allow us to modify them.
if (config.isPasspoint() && uid == Process.WIFI_UID) {
return true;
}
// EAP-SIM/AKA/AKA' network needs framework to update the anonymous identity provided
// by authenticator back to the WifiConfiguration object.
// Since it is "owned" by us, so always allow us to modify them.
if (config.enterpriseConfig != null
&& uid == Process.WIFI_UID
&& TelephonyUtil.isSimEapMethod(config.enterpriseConfig.getEapMethod())) {
return true;
}
final DevicePolicyManagerInternal dpmi = LocalServices.getService(
DevicePolicyManagerInternal.class);
final boolean isUidDeviceOwner = dpmi != null && dpmi.isActiveAdminWithPolicy(uid,
DeviceAdminInfo.USES_POLICY_DEVICE_OWNER);
// If |uid| corresponds to the device owner, allow all modifications.
if (isUidDeviceOwner) {
return true;
}
final boolean isCreator = (config.creatorUid == uid);
// Check if the |uid| holds the |NETWORK_SETTINGS| permission if the caller asks us to
// bypass the lockdown checks.
if (ignoreLockdown) {
return mWifiPermissionsUtil.checkNetworkSettingsPermission(uid);
}
// Check if device has DPM capability. If it has and |dpmi| is still null, then we
// treat this case with suspicion and bail out.
if (mContext.getPackageManager().hasSystemFeature(PackageManager.FEATURE_DEVICE_ADMIN)
&& dpmi == null) {
Log.w(TAG, "Error retrieving DPMI service.");
return false;
}
// WiFi config lockdown related logic. At this point we know uid is NOT a Device Owner.
final boolean isConfigEligibleForLockdown = dpmi != null && dpmi.isActiveAdminWithPolicy(
config.creatorUid, DeviceAdminInfo.USES_POLICY_DEVICE_OWNER);
if (!isConfigEligibleForLockdown) {
return isCreator || mWifiPermissionsUtil.checkNetworkSettingsPermission(uid);
}
final ContentResolver resolver = mContext.getContentResolver();
final boolean isLockdownFeatureEnabled = Settings.Global.getInt(resolver,
Settings.Global.WIFI_DEVICE_OWNER_CONFIGS_LOCKDOWN, 0) != 0;
return !isLockdownFeatureEnabled
&& mWifiPermissionsUtil.checkNetworkSettingsPermission(uid);
}
As far I can see, only the following uids have access to modify network configurations.
System app
Device owner
Creator (It is failing for some reason)
I am getting the same behaviour in these two phones.
Pixel 2 (Oreo 8.0.0)
Samsung J8 (Oreo 8.0.0)
Additionally, Samsung J8 always shows this warning:
CertificateException: java.security.cert.CertPathValidatorException: Trust anchor for certificate path not found
Question:
How can an already created Wi-Fi configuration be updated programmatically?
Is it even possible to update the Wi-Fi configuration once it is created in the Wi-Fi's internal database?
Is it mandatory to disconnect Wi-Fi before updating or enabling the configuration?

After digging the source code, finally got answers to my questions.
Question: Is it possible to update the configurations once it is created?
Answer: Yes, Android os allows you to update the configuration created from your application. When I called wifiManager.addNetwork(), in the log window the following statements were printed.
2019-01-04 12:23:16.168 1328-3114/? I/addOrUpdateNetwork: uid = 10190 SSID "testing-tls" nid=-1
2019-01-04 12:23:16.169 1328-1851/? V/WifiConfigManager: Adding/Updating network testing-tls
2019-01-04 12:23:16.193 1328-1851/? D/WifiConfigManager: addOrUpdateNetworkInternal: added/updated config. netId=6 configKey="testing-tls"WPA_EAP uid=10190 name=in.ac.iisc.wifimonitoring vendorAP=false hiddenSSID=false autoReconnect=1
2019-01-04 12:23:16.204 1328-1851/? D/WifiConfigStore: Writing to stores completed in 7 ms.
2019-01-04 12:23:16.205 1328-1851/? D/WifiIssueDetector: report htime=2019-01-04_12:23:16 time=1546584796205 rid=105 callBy=in.ac.iisc.wifimonitoring apiName=addOrUpdateNetwork netid=6 callUid=in.ac.iisc.wifimonitoring
2019-01-04 12:23:16.206 15873-15873/in.ac.iisc.wifimonitoring I/WifiMonitorService: WifiMonitorService, #addNetwork returned: 6
Question: what is "UID 10189 does not have permission to update configuration error" in Oreo?
Answer: After updating the configuration, we have to call wifimanager.enableNetwork() method to establish a connection to the desired access point. Workflow of EnableNetwork() is as follows.
WifiManager.enableNetwork() internally calls SyncEnableNetwork() method of WifiStateMachine class.
WifiStateMachine is the core class which tracks the state of Wifi connectivity. All event handling and all changes in connectivity state are initiated in this class.
SyncEnableNetwork() method sends CMD_ENABLE_NETWORK message to ConnectModeState class.
If disableOthers is true, call connectToUserSelectNetwork() method and passes networkId, calling UID and force reconnect [always false - hardcoded value] as arguments.
If an app does not have all the necessary permissions to update the configuration [uses checkAndUpdateLastUid() method in WifiConfigManager class - returns true only for system settings/sysui app] or if enabling of a network is failed, the following statements will be printed.
2018-12-28 12:23:44.571 1320-1847/? E/WifiConfigManager: UID 10189 does not have permission to update configuration "testing-tls"WPA_EAP
2018-12-28 12:23:44.571 1320-1847/? I/WifiStateMachine: connectToUserSelectNetwork Allowing uid 10189 with insufficient permissions to connect=1
Note: checkAndUpdateLastUid() method has been renamed to updateLastConnectUid() in Android Pie. They have slightly modified its functionality as well.
For more information, please refer to the below diagram [I am no good in drawing flowcharts. Please bear with me or suggest if any changes required].
Question 3: Is it mandatory to disconnect wifi before updating or enabling the configuration?
Answer: OS triggers a connection/reconnection to a network under the following conditions:
Selected network id must be different from currently connected network id.
If forceReconnect argument is true, Android prepares for reconnection [True only for system settings/sysui app].
Since developer apps do not have the ability to a force connection, we should disconnect the wifi in order to connect/reconnect to the network after updating the configuration.
Hope this will help others.

Android - Why ConnectivityManager.isActiveNetworkMetered always returning true (even when on Wifi)

In my music streaming app for Android, the code path below helps decides between a high bitrate stream vs. a lower bitrate based on values returned by the ConnectivityManager class instance.
I am trying to understand why ConnectivityManager.isActiveNetworkMetered() would return "true", when it's evident I'm on a local Wifi network. Take the following Android/Java code:
boolean isMetered = false;
boolean isWifi = false;
boolean isEthernet = false;
boolean isRoaming = false;
boolean isConnected = false;
NetworkInfo netinfo = connManager.getActiveNetworkInfo();
if (netinfo != null)
{
isWifi = (netinfo.getType() == ConnectivityManager.TYPE_WIFI);
isEthernet = (netinfo.getType() == ConnectivityManager.TYPE_ETHERNET);
isRoaming = netinfo.isRoaming();
isConnected = netinfo.isConnected();
Log.d(TAG, "active network type = " + netinfo.getTypeName());
Log.d(TAG, "active network subtype = " + netinfo.getSubtypeName());
Log.d(TAG, "isConnected = " + isConnected);
Log.d(TAG, "isWifi = " + isWifi);
Log.d(TAG, "isEthernet = " + isEthernet);
Log.d(TAG, "isRoaming = " + isRoaming);
}
// isActiveNetworkMetered was introduced in API 16 (Jelly Bean)
if (android.os.Build.VERSION.SDK_INT >= 16)
{
isMetered = connManager.isActiveNetworkMetered();
Log.d(TAG, "isMetered = " + isMetered);
}
When I have Wifi turned off and my only connection is to AT&T's LTE network, it prints out the following to the log console:
active network type = mobile
active network subtype = LTE
isConnected = true
isWifi = false
isEthernet = false
isRoaming = false
isMetered = true
Everything above matches expectations - I'm on a mobile carrier network that is metered.
Now switch to my home Wifi and the same block of code prints this:
active network type = WIFI
active network subtype =
isConnected = true
isWifi = true
isEthernet = false
isRoaming = false
isMetered = true
Why is isMetered, the result of isActiveNetworkMetered, still showing as true? This is causing the following code path to favor the lower bitrate stream even though I'm on my home wifi network:
if ((isWifi || isEthernet) && !isMetered)
{
result = BITRATE_HIGH_KBIT_SEC;
}
else
{
result = BITRATE_LOW_KBIT_SEC;
}
How does isActiveNetworkMetered() decide if the network is metered? Is this part of the WIFI negotiation or a bit in the SSID broadcast? A network setting on Android? I couldn't find any setting on my Android Kitkat device that let me toggle or discover the setting for a metered network.
Last week I my ISP (Frontier) sent me a new Wifi router. Possibly related? I didn't see anything on the router's firmware pages for such a setting.
I'm going to swing by work later today to see how it behaves on another network. In any case, I'm likely to edit the above code to skip the metered check unless I can prove its just an incorrect setting somewhere.
UPDATE - issue of always returning metered network reproduces on my HTC One M8 phone (running Kitkat), but not on my Nexus 7 from 2012 (also upgraded to Android 4.4 Kitkat).
PROBLEM SOLVED - it turns out my Wifi was flagged by my phone as a "Mobile Hotspot". More details on how to find and toggle this flag is here.

I've tested this too, but I'm observing the "expected" result: false for WiFi and true for 3G. This is in a Nexus 4 with Android 4.4.2.
Curiously enough the ConnectivityManagerCompat class in the support library does return false for WiFi.
final int type = info.getType();
switch (type) {
case TYPE_MOBILE:
return true;
case TYPE_WIFI:
return false;
default:
// err on side of caution
return true;
}
EDIT - Found it (I think)
NetworkPolicyManagerService seems to be the class that ultimately produces the result for this method. And according to it, WiFi connections can indeed be metered. It contains a BroadcastReceiver that "listen(s) for wifi state changes to catch metered hint" (line 567). This information is obtained from NetworkInfo.getMeteredHint(), which, on closer inspection, contains this interesting comment:
/**
* Flag indicating that AP has hinted that upstream connection is metered,
* and sensitive to heavy data transfers.
*/
private boolean mMeteredHint;
This flag is loaded from DhcpResults.hasMeteredHint()
/**
* Test if this DHCP lease includes vendor hint that network link is
* metered, and sensitive to heavy data transfers.
*/
public boolean hasMeteredHint() {
if (vendorInfo != null) {
return vendorInfo.contains("ANDROID_METERED");
} else {
return false;
}
}
So it would seem that, indeed, the AP may notify its WiFi clients that the underlying internet connection is metered by using this flag.
EDIT #2 Relevant information, from http://www.lorier.net/docs/android-metered
When an android phone is using another android phone's hotspot, it
knows it's on a "metered connection" and therefore disables the
expensive sync options ( eg: photo sync). How does it know this? The
android hotspot sends DHCP Option 43 (Vendor specific options) with
the value ANDROID_METERED. The client, if it sees ANDROID_METERED
anywhere in the option 43 values, turns on the "expensive data
connection" option.
Looks like this flag was added to "play nice" with a hotspot offered by another Android device.
EDIT #3 The commit that introduced this feature:
Connect metered DHCP hint for Wi-Fi networks.
When DHCP lease includes vendor info indicating that remote Wi-Fi
network is metered, advise NetworkPolicy. Users can still manually
change the metered flag in Settings.
You can access this setting by going:
Settings -> Data Usage -> (Overflow Menu) -> Mobile Hotspots