Expose cellular signal strength on Android to native

net/android/java/src/org/chromium/net/AndroidCellularSignalStrength.java

Index: net/android/java/src/org/chromium/net/AndroidCellularSignalStrength.java
diff --git a/net/android/java/src/org/chromium/net/AndroidCellularSignalStrength.java b/net/android/java/src/org/chromium/net/AndroidCellularSignalStrength.java
new file mode 100644
index 0000000000000000000000000000000000000000..8e062e2e8bc26b431996670315ec7c3f2da56439
--- /dev/null
+++ b/net/android/java/src/org/chromium/net/AndroidCellularSignalStrength.java
@@ -0,0 +1,161 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.net;
+
+import android.Manifest;
+import android.annotation.SuppressLint;
+import android.content.Context;
+import android.content.pm.PackageManager;
+import android.os.Build;
+import android.telephony.CellInfo;
+import android.telephony.CellInfoCdma;
+import android.telephony.CellInfoGsm;
+import android.telephony.CellInfoLte;
+import android.telephony.CellInfoWcdma;
+import android.telephony.CellSignalStrengthCdma;
+import android.telephony.CellSignalStrengthGsm;
+import android.telephony.CellSignalStrengthLte;
+import android.telephony.CellSignalStrengthWcdma;
+import android.telephony.TelephonyManager;
+
+import org.chromium.base.ContextUtils;
+import org.chromium.base.annotations.CalledByNative;
+import org.chromium.base.annotations.JNINamespace;
+
+import java.util.List;
+
+/**
+ * This class interacts with the cellular signal strength API provided by Android.

[bengr, 2016/06/10 20:57:37]

You mean specifically the SignalStrength API, right? Refer to that.

[tbansal1, 2016/06/16 00:58:12]

Done.

+ */
+@JNINamespace("net::android::cellular_signal_strength")
+public class AndroidCellularSignalStrength {
+    /**
+     * True if the Android API to query the cellular signal strength is available.
+     * getAllCellInfo is only available on API Level JELLY_BEAN_MR1 and higher.
+     * For Android M and higher, verify that appropriate permissions are already
+     * available. This ensures that Chromium would not request run-time
+     * permission from the user when querying for cellular signal strength.

[pauljensen, 2016/06/10 13:52:15]

You could probably get this info from TelephonyManager.getNeighboringCellInfo()
in earlier versions of Android if you wanted to cover those versions.

[tbansal1, 2016/06/16 00:58:12]

Added a TODO.

+     */
+    private static final boolean sAPIAvailable =
+            Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1
+            && (Build.VERSION.SDK_INT < Build.VERSION_CODES.M
+                       || ContextUtils.getApplicationContext().checkSelfPermission(

[pauljensen, 2016/06/10 13:52:15]

I don't know a whole lot about Java static initializer order, but how do you
know the context has been set this early?

[tbansal1, 2016/06/16 00:58:10]

Java static code is initialized in the order of when it is accessed.
ApplicationContext should be initialized much before anyone access this class.
https://cs.chromium.org/chromium/src/chrome/android/java/src/org/chromium/chr...

I also added a null check to avoid crash.

+                                  Manifest.permission.ACCESS_COARSE_LOCATION)
+                               == PackageManager.PERMISSION_GRANTED);
+
+    private AndroidCellularSignalStrength() {}

[bengr, 2016/06/10 20:57:37]

Are all methods private because this should only be instantiated and used from
native? Consider commenting on this somewhere.

[tbansal1, 2016/06/16 00:58:10]

Changed two of them to public since it is okay to access them from Java code.

+
+    /**
+     * @return RSSI (in dbM) for the currently registered cellular network. Returns {@link
+     * CellularSignalStrengthError.ERROR_NOT_SUPPORTED} if the RSSI is unavailable.
+     */
+    @SuppressWarnings("unused")
+    @SuppressLint("NewApi")
+    @CalledByNative
+    private static int getRssiDbm(Context context) {

[bengr, 2016/06/10 20:57:37]

Maybe rename this as getSignalStrengthDbm

[tbansal1, 2016/06/16 00:58:08]

Done.

+        List<CellInfo> cellInfos = getCellInfo(context);
+        if (cellInfos == null) {

[bengr, 2016/06/10 20:57:37]

If getCellInfo returned an empty list instead of null, you wouldn't need this
check. Alternatively, you could just create a function called
getRegisteredCellInfo() that returns one CellInfo or null.

[tbansal1, 2016/06/16 00:58:11]

Done.

+            return CellularSignalStrengthError.ERROR_NOT_SUPPORTED;
+        }
+
+        for (CellInfo cellInfo : cellInfos) {
+            if (cellInfo.isRegistered()) {
+                return getRssiDbm(cellInfo);

[bengr, 2016/06/10 20:57:37]

I don't understand. Is at most one cellInfo registered?

[tbansal1, 2016/06/16 00:58:09]

There could be multiple radios, and in that case there would be multiple
cellInfos. Added comment.

[bengr, 2016/06/20 20:07:26]

If there are multiple radios, which cellinfo do you return?

[tbansal1, 2016/06/20 21:32:03]

I return the first one, which depends on what Android returns. The Android API
does not specify the order in which it will return cellInfos. So, Chromium API
can't guarantee anything stronger.

The other option could be to return ERROR when there are multiple radios. I did
add the comment "May return incorrect result if there are multiple cellular
radios on the device" on the API.

[bengr, 2016/06/22 16:54:07]

I don't like this interface because the rssi (or signal level in the next
method) might have nothing to do with the connection used. Returning an error
seems safer, but I don't know how much coverage we lose. Another possibility is
to get the rssi/signal level for a particular connection. That makes more sense
to me but probably introduces a lot more plumbing.

+            }
+        }
+
+        return CellularSignalStrengthError.ERROR_NOT_SUPPORTED;
+    }
+
+    /**
+     * @return the signal level (between 0 and 4, both inclusive) for the currently registered
+     * cellular network. Returns {@link CellularSignalStrengthError.ERROR_NOT_SUPPORTED} if the
+     * signal level is unavailable.
+     */
+    @SuppressWarnings("unused")
+    @SuppressLint("NewApi")
+    @CalledByNative
+    private static int getSignalLevel(Context context) {

[bengr, 2016/06/10 20:57:37]

Naming suggestion: getSignalStrengthLevel

[tbansal1, 2016/06/16 00:58:09]

Done.

+        List<CellInfo> cellInfos = getCellInfo(context);
+        if (cellInfos == null) {

[bengr, 2016/06/10 20:57:37]

See comment on line 59.

[tbansal1, 2016/06/16 00:58:10]

Done.

+            return CellularSignalStrengthError.ERROR_NOT_SUPPORTED;
+        }
+
+        for (CellInfo cellInfo : cellInfos) {
+            if (cellInfo.isRegistered()) {
+                return getSignalLevel(cellInfo);
+            }
+        }
+
+        return CellularSignalStrengthError.ERROR_NOT_SUPPORTED;
+    }
+
+    /**
+    * Returns all observed cell information from all radios on the device including the primary and
+    * neighboring cells. May return null.
+    */
+    @SuppressLint("NewApi")
+    private static List<CellInfo> getCellInfo(Context context) {
+        if (!sAPIAvailable) {
+            return null;
+        }
+
+        TelephonyManager telephonyManager =
+                (TelephonyManager) context.getSystemService(Context.TELEPHONY_SERVICE);
+        if (telephonyManager == null) return null;
+
+        return telephonyManager.getAllCellInfo();
+    }
+
+    /**
+     * @return RSSI (in dbM) from {@link cellInfo}. Returns {@link
+     * CellularSignalStrengthError.ERROR_NOT_SUPPORTED} if the RSSI is
+     * unavailable.
+     */
+    @SuppressLint("NewApi")
+    private static int getRssiDbm(CellInfo cellInfo) {
+        if (cellInfo instanceof CellInfoCdma) {
+            CellSignalStrengthCdma signalStrength =
+                    ((CellInfoCdma) cellInfo).getCellSignalStrength();
+            return signalStrength.getDbm();

[pauljensen, 2016/06/10 13:52:15]

can we get rid of these signalStrength variables?  they appear to only be used
once.

[tbansal1, 2016/06/16 00:58:10]

Done.

+        } else if (cellInfo instanceof CellInfoGsm) {

[pauljensen, 2016/06/10 13:52:15]

all these "else"'s aren't needed because you return from each one.

[tbansal1, 2016/06/16 00:58:12]

Done.

+            CellSignalStrengthGsm signalStrength = ((CellInfoGsm) cellInfo).getCellSignalStrength();
+            return signalStrength.getDbm();
+        } else if (cellInfo instanceof CellInfoLte) {
+            CellSignalStrengthLte signalStrength = ((CellInfoLte) cellInfo).getCellSignalStrength();
+            return signalStrength.getDbm();
+        } else if (cellInfo instanceof CellInfoWcdma) {
+            CellSignalStrengthWcdma signalStrength =
+                    ((CellInfoWcdma) cellInfo).getCellSignalStrength();
+            return signalStrength.getDbm();
+        }
+        return CellularSignalStrengthError.ERROR_NOT_SUPPORTED;
+    }
+
+    /**
+     * @return the signal level from {@link cellInfo}. Returns {@link
+     * CellularSignalStrengthError.ERROR_NOT_SUPPORTED} if the signal
+     * level is unavailable with lower value indicating lower signal strength.
+     */
+    @SuppressLint("NewApi")
+    private static int getSignalLevel(CellInfo cellInfo) {
+        if (cellInfo instanceof CellInfoCdma) {
+            CellSignalStrengthCdma signalStrength =
+                    ((CellInfoCdma) cellInfo).getCellSignalStrength();
+            return signalStrength.getLevel();
+        } else if (cellInfo instanceof CellInfoGsm) {
+            CellSignalStrengthGsm signalStrength = ((CellInfoGsm) cellInfo).getCellSignalStrength();
+            return signalStrength.getLevel();
+        } else if (cellInfo instanceof CellInfoLte) {
+            CellSignalStrengthLte signalStrength = ((CellInfoLte) cellInfo).getCellSignalStrength();
+            return signalStrength.getLevel();
+        } else if (cellInfo instanceof CellInfoWcdma) {
+            CellSignalStrengthWcdma signalStrength =
+                    ((CellInfoWcdma) cellInfo).getCellSignalStrength();
+            return signalStrength.getLevel();
+        }
+        return CellularSignalStrengthError.ERROR_NOT_SUPPORTED;
+    }
+}