Hey there, I've worked with Hexene's LocalVPN and Android VPNService before, so I can walk you through how to add app identification for packets. Here's a step-by-step solution tailored to your needs:

1. Core Principle: Map UID to App Package Name #

Every Android app has a unique UID (User Identifier) assigned by the system. The key is to retrieve the UID associated with each incoming packet in your VPN service, then convert that UID to the corresponding app package name using Android's PackageManager.

2. Step-by-Step Implementation #

2.1 Modify Hexene's Packet Handling Logic #

Hexene's core runs on a subclass of VpnService, where it reads and processes traffic from the TUN interface. You'll need to insert UID retrieval logic at the point where packets are read:

• For Android 8.0+ (API 26+), the VpnService class provides a built-in getUidForPacket(byte[] packet, int length) method that directly returns the UID of the app sending the packet.
• For older API versions, you'll need a workaround (more on that later), but let's start with the modern approach first.

Here's how to integrate this into Hexene's main service code:

public class LocalVpnService extends VpnService implements Runnable {
    private ParcelFileDescriptor vpnInterface;
    private FileInputStream in;
    private FileOutputStream out;
    private PackageManager packageManager;
    private HashMap<Integer, String> uidPackageCache = new HashMap<>(); // Cache to avoid repeated lookups

    @Override
    public void onCreate() {
        super.onCreate();
        packageManager = getPackageManager();
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        setupVpnTunnel();
        new Thread(this).start();
        return START_STICKY;
    }

    private void setupVpnTunnel() {
        try {
            Builder vpnBuilder = new Builder();
            vpnBuilder.addAddress("10.0.0.2", 32);
            vpnBuilder.addRoute("0.0.0.0", 0);
            vpnBuilder.addDnsServer("8.8.8.8");
            vpnInterface = vpnBuilder.setSession("Hexene LocalVPN").establish();
            in = new FileInputStream(vpnInterface.getFileDescriptor());
            out = new FileOutputStream(vpnInterface.getFileDescriptor());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    @Override
    public void run() {
        byte[] packetBuffer = new byte[1500]; // Standard MTU size
        while (!Thread.currentThread().isInterrupted()) {
            try {
                int packetLength = in.read(packetBuffer);
                if (packetLength > 0) {
                    // Get UID for the incoming packet
                    int appUid = getUidForPacket(packetBuffer, packetLength);
                    // Convert UID to package name (with caching)
                    String appPackage = getCachedPackageName(appUid);

                    if (appPackage != null) {
                        Log.d("VPN_DEBUG", "Packet from app: " + appPackage);
                        // Check if this is your target app
                        if ("com.your.target.app".equals(appPackage)) {
                            processTargetAppPacket(packetBuffer, packetLength);
                        } else {
                            // Forward other packets as usual
                            out.write(packetBuffer, 0, packetLength);
                        }
                    }
                }
            } catch (Exception e) {
                e.printStackTrace();
                break;
            }
        }
    }
}

2.2 Implement UID-to-Package-Name Conversion #

Add these helper methods to convert UIDs to package names, with caching to avoid performance hits from repeated PackageManager calls:

private String getCachedPackageName(int uid) {
    if (uidPackageCache.containsKey(uid)) {
        return uidPackageCache.get(uid);
    }

    String[] packages = packageManager.getPackagesForUid(uid);
    String targetPackage = null;
    if (packages != null && packages.length > 0) {
        targetPackage = packages[0]; // Most apps have one package per UID; adjust if handling shared UIDs
        uidPackageCache.put(uid, targetPackage);
    }
    return targetPackage;
}

private void processTargetAppPacket(byte[] buffer, int length) {
    // Add your custom logic here: log traffic, modify packets, block requests, etc.
    try {
        // Example: Forward the packet after processing
        out.write(buffer, 0, length);
    } catch (IOException e) {
        e.printStackTrace();
    }
}

2.3 Handle API Compatibility (Pre-Android 8.0) #

If you need to support devices below API 26, you'll need to use a netlink socket to retrieve packet UIDs (since getUidForPacket() doesn't exist). This requires more low-level code, but here's a high-level outline:

• Create a netlink socket to listen for NETLINK_INET_DIAG messages.
• Map packet source/destination ports to UIDs using TrafficStats or the netlink data.
• Note: This approach is more complex and may require JNI or reflection for some system calls.

2.4 Required Permissions #

Update your AndroidManifest.xml to include all necessary permissions:

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.BIND_VPN_SERVICE" />
<!-- For API 30+: Required to query package names for all apps -->
<uses-permission android:name="android.permission.QUERY_ALL_PACKAGES"
    tools:ignore="QueryAllPackagesPermission" />

<application ...>
    <service
        android:name=".LocalVpnService"
        android:permission="android.permission.BIND_VPN_SERVICE">
        <intent-filter>
            <action android:name="android.net.VpnService" />
        </intent-filter>
    </service>
</application>

3. Key Hexene-Specific Notes #

• Locate Hexene's core packet processing loop (usually in LocalVpnService or a dedicated VpnThread class) and insert the UID/package name logic there.
• If Hexene uses DatagramChannel instead of direct file stream reads, you'll still need to pass the raw packet data to getUidForPacket() to retrieve the UID.

4. Common Pitfalls to Avoid #

• Performance: Caching UID-to-package mappings is critical—avoid calling getPackagesForUid() for every packet.
• Shared UIDs: Some system apps or apps with shared UIDs will return multiple package names; adjust your logic to handle this case if needed.
• VPN Authorization: Ensure your app prompts the user to grant VPN access on first launch—without this, the service won't start.

内容的提问来源于stack exchange，提问作者user3307598