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..ac4df038617e59cc978047d5882b3a2344fb9f0b
--- /dev/null
+++ b/net/android/java/src/org/chromium/net/AndroidCellularSignalStrength.java
@@ -0,0 +1,147 @@
+// 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.os.Process;
+import android.telephony.CellInfo;
+import android.telephony.CellInfoCdma;
+import android.telephony.CellInfoGsm;
+import android.telephony.CellInfoLte;
+import android.telephony.CellInfoWcdma;
+import android.telephony.TelephonyManager;
+
+import org.chromium.base.ContextUtils;
+import org.chromium.base.annotations.CalledByNative;
+import org.chromium.base.annotations.JNINamespace;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * This class interacts with the CellInfo API provided by Android.
+ */
+@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.
+     * Also verify that appropriate permissions are already available. This
+     * ensures that on Android M and higher, Chromium would not request run-time
+     * permission from the user when querying for cellular signal strength.
+     * TODO(tbansal): Consider using TelephonyManager.getNeighboringCellInfo()
+     * for earlier versions of Android.
+     */
+    private static final boolean sAPIAvailable =
+            Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1
+            && ContextUtils.getApplicationContext() != null

[pauljensen, 2016/06/24 11:53:14]

The null-check here indicates a silent failure condition which isn't good. 
Considering all the public APIs here include a Context, why not have a lazily
initialized variable instead that uses the passed in Context to calculate
whether the permissions are available?

[tbansal1, 2016/06/27 19:01:17]

Done.

+            && ContextUtils.getApplicationContext().checkPermission(
+                       Manifest.permission.ACCESS_COARSE_LOCATION, Process.myPid(), Process.myUid())
+                    == PackageManager.PERMISSION_GRANTED;
+
+    /**
+     * @return Signal strength (in dbM) for the currently registered cellular network. Returns
+     * {@link CellularSignalStrengthError.ERROR_NOT_SUPPORTED} if the signal strength is
+     * unavailable or if there are multiple cellular radios on the device.
+     */
+    @SuppressLint("NewApi")
+    @CalledByNative
+    public static int getSignalStrengthDbm(Context context) {
+        List<CellInfo> cellInfos = getRegisteredCellInfo(context);
+        return cellInfos == null || cellInfos.size() != 1
+                ? CellularSignalStrengthError.ERROR_NOT_SUPPORTED
+                : getSignalStrengthDbm(cellInfos.get(0));
+    }
+
+    /**
+     * @return the signal strength level (between 0 and 4, both inclusive) for the currently
+     * registered cellular network. Returns {@link CellularSignalStrengthError.ERROR_NOT_SUPPORTED}
+     * if the signal strength level is unavailable or if there are multiple cellular radios on the
+     * device.
+     */
+    @SuppressWarnings("unused")
+    @SuppressLint("NewApi")
+    @CalledByNative
+    public static int getSignalStrengthLevel(Context context) {
+        List<CellInfo> cellInfos = getRegisteredCellInfo(context);
+        return cellInfos == null || cellInfos.size() != 1
+                ? CellularSignalStrengthError.ERROR_NOT_SUPPORTED
+                : getSignalStrengthLevel(cellInfos.get(0));
+    }
+
+    /**
+     * Returns all observed cell information from all radios on the device including the primary
+     * and neighboring cells. Returns only the information of cells that are registered to a
+     * mobile network. May return null.
+     */
+    @SuppressLint("NewApi")
+    private static List<CellInfo> getRegisteredCellInfo(Context context) {
+        if (!sAPIAvailable) {
+            return null;
+        }
+
+        TelephonyManager telephonyManager =
+                (TelephonyManager) context.getSystemService(Context.TELEPHONY_SERVICE);
+        if (telephonyManager == null) return null;

[pauljensen, 2016/06/24 11:53:14]

I think Chrome style is not to put if-statement clauses on the same line as the
if-condition.  Please make this consistent with line 86.

[tbansal1, 2016/06/27 19:01:17]

Done.

+
+        List<CellInfo> cellInfos = telephonyManager.getAllCellInfo();
+        if (cellInfos == null) return null;
+
+        List<CellInfo> registeredCellInfos = new ArrayList<CellInfo>();
+        for (CellInfo cellInfo : cellInfos) {
+            if (cellInfo.isRegistered()) {
+                registeredCellInfos.add(cellInfo);
+            }
+        }
+        return registeredCellInfos;
+    }
+
+    /**
+     * @return Signal strength (in dbM) from {@link cellInfo}. Returns {@link
+     * CellularSignalStrengthError.ERROR_NOT_SUPPORTED} if the signal strength is unavailable.
+     */
+    @SuppressLint("NewApi")
+    private static int getSignalStrengthDbm(CellInfo cellInfo) {
+        if (cellInfo instanceof CellInfoCdma) {
+            return ((CellInfoCdma) cellInfo).getCellSignalStrength().getDbm();
+        }
+        if (cellInfo instanceof CellInfoGsm) {
+            return ((CellInfoGsm) cellInfo).getCellSignalStrength().getDbm();
+        }
+        if (cellInfo instanceof CellInfoLte) {
+            return ((CellInfoLte) cellInfo).getCellSignalStrength().getDbm();
+        }
+        if (cellInfo instanceof CellInfoWcdma) {
+            return ((CellInfoWcdma) cellInfo).getCellSignalStrength().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 getSignalStrengthLevel(CellInfo cellInfo) {
+        if (cellInfo instanceof CellInfoCdma) {
+            return ((CellInfoCdma) cellInfo).getCellSignalStrength().getLevel();
+        }
+        if (cellInfo instanceof CellInfoGsm) {
+            return ((CellInfoGsm) cellInfo).getCellSignalStrength().getLevel();
+        }
+        if (cellInfo instanceof CellInfoLte) {
+            return ((CellInfoLte) cellInfo).getCellSignalStrength().getLevel();
+        }
+        if (cellInfo instanceof CellInfoWcdma) {
+            return ((CellInfoWcdma) cellInfo).getCellSignalStrength().getLevel();
+        }
+        return CellularSignalStrengthError.ERROR_NOT_SUPPORTED;
+    }
+}