Can someone explain how TrafficStats works its magic in the Android OS?
<p>I've written a nice little Android app to check data usage, unfortunately it relies heavily on android.net.TrafficStats which was introduced with Froyo (Android 2.2).</p>

<p>I'm attempting to back-port this class for my non-Froyo users, and what I'm able to determine from the <a href="http://android.git.kernel.org/?p=platform/frameworks/base.git;a=blob;f=core/jni/android_net_TrafficStats.cpp;h=ff46bdd2ba39380a0a673cbf8aadfc5a3529156c;hb=refs/heads/master1." rel="nofollow">Android source</a> is:</p>

<ol>
<li>TrafficStats.java is just a native pointer to a c file</li>
<li>The c file opens two files (see below) and reads their contents</li>
<li>If either contains a numeric value it spits it back as the "bytes used" count </li>
</ol>

<p>Here's my challenge... when I call TrafficStats via the API on my device, I get a reading (ex. 1113853 bytes). When I open the two files and check their contents, one file doesn't exist and the other file is 0 bytes.  </p>

<p>So clearly I mis-understood what TrafficStats is doing. Can anyone shed some light on how it's working it's magic? </p>

<p>Thanks for the help. </p>

<p>(here is my attempt to port the c file to java)</p>

<pre><code>package com.suttco.net;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;

import com.suttco.IOUtils;
import com.suttco.StringUtils;

import android.util.Log;

public class TrafficStatsFile {

 private static final String mobileRxFile_1 = "/sys/class/net/rmnet0/statistics/rx_bytes";
 private static final String mobileRxFile_2 = "/sys/class/net/ppp0/statistics/rx_bytes";
 private static final String mobileTxFile_1 = "/sys/class/net/rmnet0/statistics/tx_bytes";
 private static final String mobileTxFile_2 = "/sys/class/net/ppp0/statistics/tx_bytes";

 private static final String LOGGING_TAG = TrafficStatsFile.class.getSimpleName();

 public long getMobileRxBytes() {
  return tryBoth(mobileRxFile_1, mobileRxFile_2);
 }

 public long getMobileTxBytes() {
  return tryBoth(mobileTxFile_1, mobileTxFile_2);
 }

 // Return the number from the first file which exists and contains data
 private static long tryBoth(String a, String b) {
  long num = readNumber(a);
  return num &gt;= 0 ? num : readNumber(b);
 }

 // Returns an ASCII decimal number read from the specified file, -1 on error.
 private static long readNumber(String filename) {
  File f = new File(filename);
  if(f.exists()) {
   if(f.canRead()) {
    try {
     Log.d(LOGGING_TAG, "f.length() = " + f.length());
     String contents = IOUtils.readFileAsString(f);
     if(StringUtils.IsNotNullOrEmpty(contents)) {
      try {
       return Long.parseLong(contents);
      }
      catch(NumberFormatException nfex) {
       Log.w(LOGGING_TAG, "File contents are not numeric: " + filename); 
      }
     }
     else {
      Log.w(LOGGING_TAG, "File contents are empty: " + filename); 
     }
    }
    catch (FileNotFoundException fnfex) {
     Log.w(LOGGING_TAG, "File not found: " + filename, fnfex);
    }
    catch(IOException ioex) {
     Log.w(LOGGING_TAG, "IOException: " + filename, ioex);
    }
   }
   else {
    Log.w(LOGGING_TAG, "Unable to read file: " + filename);
   }
  }
  else {
   Log.w(LOGGING_TAG, "File does not exist: " + filename);
  }
  return -1;
 }
}
</code></pre>
