PCAPdroid/docs/app_api.md

PCAPdroid exposes an API for other apps to configure and control the packet capture. This can be used to easily enable packet capture in your app, provided that the PCAPdroid app is also installed into the device.

The API

The CaptureCtrl.java activity is the one exposed to allow you to control the PCAPdroid capture via Intents.

The activity can be easily invoked from the cli by running:

adb shell am start -e action [ACTION] -e [SETTINGS] -n com.emanuelef.remote_capture/.activities.CaptureCtrl

where ACTION is one of:

• start: starts the capture with the specified parameters
• stop: stops the capture
• get_status: get the capture status

The capture parameters are specified via Intent extras, which are discussed below. A common task is to capture the traffic of a specific app to analyze it into your app. This can be easily accomplished by running PCAPdroid in the UDP Exporter mode:

adb shell am start -e action start -e pcap_dump_mode udp_exporter -e collector_ip_address 127.0.0.1 -e collector_port 5123 -e app_filter org.mozilla.firefox -n com.emanuelef.remote_capture/.activities.CaptureCtrl

then your app can listen for UDP packets on port 5123 to handle the Firefox network packets. Another interesting option is to enable the pcapdroid_trailer to be able to get the app UID/name into your app.

The Intent above can also be triggered programmatically from your app:

class YourActivity extends Activity {
  private final ActivityResultLauncher<Intent> captureLauncher =
    registerForActivityResult(new StartActivityForResult(), this::handleCaptureResult);

  void startCapture() {
    Intent intent = new Intent(Intent.ACTION_VIEW);
    intent.setClassName("com.emanuelef.remote_capture", "com.emanuelef.remote_capture.activities.CaptureCtrl");

    intent.putExtra("action", "start");
    intent.putExtra("pcap_dump_mode", "udp_exporter");
    intent.putExtra("collector_ip_address", "127.0.0.1");
    intent.putExtra("collector_port", "5123");
    intent.putExtra("app_filter", "org.mozilla.firefox");

    captureLauncher.launch(intent);
  }

  void handleCaptureResult(final ActivityResult result) {
    if(result.getResultCode() == RESULT_OK) {
      // command executed successfully
    }
  }
}

The result code tells if the command succeded or not. Check out the PCAPReceiver sample app for a working example.

User Consent

To prevent malicious apps from monitoring/hijacking the device traffic, PCAPdroid will ask for user consent every time a capture is started. If the user denies consent, then the request fails. After an app is granted start permission, subsequent requests from that app are automatically granted.

From the permission dialog the user can choose to permanently grant or deny the capture permission to an app. The permanently granted/denied permissions can be edited from the Control Permissions entry in the PCAPdroid settings.

Applications interfacing with PCAPdroid should use the startActivityForResult (or the equivalent ActivityResultLauncher) when calling its API, rather than startActivity. This ensures that the package name of the calling app can be retrieved via getCallingPackage.

Capture Settings

As shown above, the capture settings can be specified by using intent extras. The updated list of all the supported parameters is available in CaptureSettings.java.

Parameter	Type	Ver	Value
pcap_dump_mode	string		none | http_server | udp_exporter | pcap_file
app_filter	string		the package name of the app to capture
collector_ip_address	string		the IP address of the collector in udp_exporter mode
collector_port	int		the UDP port of the collector in udp_exporter mode
http_server_port	int		the HTTP server port in http_server mode
pcap_uri	string		the URI for the PCAP dump in pcap_file mode
tls_decryption_enabled	bool		true to enable the SOCKS5 proxy (e.g. for TLS decryption)
socks5_proxy_ip_address	string		the IP address of the SOCKS5 proxy
socks5_proxy_port	int		the TCP port of the SOCKS5 proxy
ipv6_enabled	bool		true to enable IPv6 support in non-root mode
root_capture	bool		true to capture packets in root mode, false to use the VPNService
pcapdroid_trailer	bool		true to enable the PCAPdroid trailer
capture_interface	string	42	@inet | any | ifname - network interface to use in root mode
snaplen	int	43	max size in bytes for each individual packet in the PCAP dump
max_pkts_per_flow	int	43	only dump the first max_pkts_per_flow packets per flow
max_dump_size	int	43	PCAP dump max bytes before the capture is automatically stopped

The Ver column indicates the minimum PCAPdroid version required to use the given parameter. The PCAPdroid version can be queried via the get_status action as explained below.

NOTE: due to file storage restrictions, the pcap_uri must point to an app internal directory, e.g. file:///data/user/0/com.emanuelef.remote_capture/cache/dump.pcap.

Query the Capture Status

It is possible to check if the capture is currently running by sending an Intent with the get_status action. The response Intent contains the following extras:

Field	Type	Value
version_name	string	the PCAPdroid versionName (e.g. "1.4.5")
version_code	int	the PCAPdroid versionCode, an incremental number for the release
running	bool	true if the capture is running

Other than via the API, the capture may be manually stopped by the user from the PCAPdroid app. In order to be notified when the capture is stopped, you can create a BroadcastReceiver and subscribe to the com.emanuelef.remote_capture.CaptureStatus action. Here is an example:

<receiver android:name=".MyBroadcastReceiver"
    android:enabled="true"
    android:exported="true">
    <intent-filter>
        <action android:name="com.emanuelef.remote_capture.CaptureStatus" />
    </intent-filter>
</receiver>

To tell PCAPdroid to send the Intent to your receiver, you must specify its class name in the broadcast_receiver extra of the start intent:

intent.putExtra("action", "start");
intent.putExtra("broadcast_receiver", "com.emanuelef.pcap_receiver.MyBroadcastReceiver");
...
captureStartLauncher.launch(intent);

The receiver will get an intent with the running extra set to false when the capture is stopped.

Dumping PCAP to file

Due to the restrictions introduced via the scoped storage, PCAPdroid can only create files inside its private directory, which is not accessible to you as a user. To dump the PCAP file to a publicly available directory, you must first perform the following steps:

1. Open PCAPdroid and select the "PCAP File" dump mode
2. Start the capture and select the path of the file to write. In this example I assume you select the /sdcard/test.pcap file
3. Stop the capture and choose to keep the generated PCAP file (don't delete it!)
4. Retrieve the internal URL which Android uses to reference this file. You can find this in the logcat output of PCAPdroid:

D/Main: PCAP URI to write [persistable=true]: content://com.android.externalstorage.documents/document/primary%3Atest.pcap

You should now be able to write the test.pcap file by setting the pcap_uri to this URI. You must repeat the steps above if you delete the file.

NOTE: if the messages shows [persistable=false] then it was not possible to get the permissions on the URI, so the pcap_uri paramter won't work. This occurs on devices without a file manager to select the PCAP destination path (e.g. on Android TV).