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..6ef2c78400d315bf1c9ec63168f4e0e915a26103
--- /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.TargetApi;
+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.annotations.CalledByNative;
+import org.chromium.base.annotations.JNINamespace;
+
+import java.util.Iterator;
+import java.util.List;
+
+/**
+ * This class interacts with the CellInfo API provided by Android. This class is thread safe.
+ */
+@JNINamespace("net::android::cellular_signal_strength")
+public class AndroidCellularSignalStrength {
+    /**
+     * @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.
+     */
+    @TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR1)
+    @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 with lower value indicating lower signal strength. Returns
+     * {@link CellularSignalStrengthError#ERROR_NOT_SUPPORTED} if the signal strength level is
+     * unavailable or if there are multiple cellular radios on the device.
+     */
+    @TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR1)
+    @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 true if the API for quering the signal strength is available.
+     * {@link TelephonyManager#getAllCellInfo} is only available on API Level
+     * {@link Build.VERSION_CODES#JELLY_BEAN_MR1} and higher. Also verifies that appropriate
+     * permissions are already available. This ensures that on Android M and higher, Chromium will
+     * not request run-time permission from the user when querying for cellular signal strength.
+     * TODO(tbansal): Consider using {@link TelephonyManager#getNeighboringCellInfo}
+     * for earlier versions of Android.
+    */
+    private static boolean isAPIAvailable(Context context) {
+        return Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1
+                && context.checkPermission(Manifest.permission.ACCESS_COARSE_LOCATION,
+                           Process.myPid(), Process.myUid())
+                == PackageManager.PERMISSION_GRANTED;
+    }
+
+    /**
+     * 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 {@code null}.
+     */
+    @TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR1)
+    private static List<CellInfo> getRegisteredCellInfo(Context context) {
+        if (!isAPIAvailable(context)) {
+            return null;
+        }
+
+        TelephonyManager telephonyManager =
+                (TelephonyManager) context.getSystemService(Context.TELEPHONY_SERVICE);
+        if (telephonyManager == null) {
+            return null;
+        }
+
+        List<CellInfo> cellInfos = telephonyManager.getAllCellInfo();
+        if (cellInfos == null) {
+            return null;
+        }
+
+        Iterator<CellInfo> iter = cellInfos.iterator();
+        while (iter.hasNext()) {
+            if (!iter.next().isRegistered()) {
+                iter.remove();
+            }
+        }
+        return cellInfos;
+    }
+
+    /**
+     * @return Signal strength (in dbM) from {@link cellInfo}. Returns {@link
+     * CellularSignalStrengthError#ERROR_NOT_SUPPORTED} if the signal strength is unavailable.
+     */
+    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.
+     */
+    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;
+    }
+}