Always short backoff on charging

app/src/main/java/eu/faircode/email/Helper.java

@@ -37,6 +37,7 @@ import android.content.res.Resources;
 import android.content.res.TypedArray;
 import android.graphics.Color;
 import android.net.Uri;
+import android.os.BatteryManager;
 import android.os.Build;
 import android.os.Bundle;
 import android.os.Environment;
@@ -423,6 +424,18 @@ public class Helper {
         return null;
     }
 
+    static boolean isCharging(Context context) {
+        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.M)
+            return false;
+        try {
+            BatteryManager bm = (BatteryManager) context.getSystemService(Context.BATTERY_SERVICE);
+            return bm.isCharging();
+        } catch (Throwable ex) {
+            Log.e(ex);
+            return false;
+        }
+    }
+
     static boolean isPlayStoreInstall() {
         return BuildConfig.PLAY_STORE_RELEASE;
     }

app/src/main/java/eu/faircode/email/Log.java

@@ -1292,6 +1292,7 @@ public class Log {
         if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M)
             ignoring = pm.isIgnoringBatteryOptimizations(BuildConfig.APPLICATION_ID);
         sb.append(String.format("Battery optimizations: %b\r\n", !ignoring));
+        sb.append(String.format("Charging: %b\r\n", Helper.isCharging(context)));
 
         if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.P) {
             UsageStatsManager usm = (UsageStatsManager) context.getSystemService(Context.USAGE_STATS_SERVICE);

app/src/main/java/eu/faircode/email/ServiceSynchronize.java

@@ -1711,7 +1711,8 @@ public class ServiceSynchronize extends ServiceBase implements SharedPreferences
                     long fail_threshold = account.poll_interval * 60 * 1000L * 2 / 3;
                     if (account.last_connected == null ||
                             now - account.last_connected < fail_threshold) {
-                        if (state.getBackoff() == CONNECT_BACKOFF_START) {
+                        if (state.getBackoff() == CONNECT_BACKOFF_START &&
+                                !Helper.isCharging(this)) {
                             fast_fails++;
                             if (fast_fails == 1)
                                 first_fail = now;
@@ -1838,9 +1839,10 @@ public class ServiceSynchronize extends ServiceBase implements SharedPreferences
 
                     if (backoff < max)
                         state.setBackoff(backoff * 2);
-                    else if (backoff == max)
-                        state.setBackoff(CONNECT_BACKOFF_ALARM_START * 60);
-                    else if (backoff < CONNECT_BACKOFF_ALARM_MAX * 60)
+                    else if (backoff == max) {
+                        if (!Helper.isCharging(this))
+                            state.setBackoff(CONNECT_BACKOFF_ALARM_START * 60);
+                    } else if (backoff < CONNECT_BACKOFF_ALARM_MAX * 60)
                         state.setBackoff(backoff * 2);
                 }