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	Mode	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
socks5_enabled	bool		vpn	true to redirect the TCP connections to a SOCKS5 proxy
socks5_proxy_ip_address	string		vpn	the IP address of the SOCKS5 proxy
socks5_proxy_port	int		vpn	the TCP port of the SOCKS5 proxy
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		root	@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		max size in bytes for the PCAP dump
tls_decryption	bool	49	vpn	true to enable the built-in TLS decryption
block_quic	bool	51	vpn	true to block QUIC traffic
auto_block_private_dns	bool	51	vpn	true to detect and possibly block private DNS to inspect traffic
ip_mode	string	56	vpn	which IP addresses to use for the VPN: ipv4 | ipv6 | both

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. The Mode column indicates if the option applies to any mode or only to the VPN or root mode.

NOTE: for security reasons, since version 1.5.3 you cannot specify a remote server IP address in collector_ip_address or in socks5_proxy_ip_address. If you really want to do this, you should first set such a remote IP address via the PCAPdroid gui and only then invoke the API.

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.

Capture Stats

In the result of the stop and get_status actions and in the broadcast of CaptureStatus, PCAPdroid provides the following capture stats in the form of Intent extras:

Field	Type	Ver	Value
bytes_sent	long	50	bytes sent (from the device to the Internet)
bytes_rcvd	long	50	bytes received (from the Internet to the device)
bytes_dumped	long	50	size of the PCAP dump
pkts_sent	int	50	packets sent
pkts_rcvd	int	50	packets received
pkts_dropped	int	50	in root mode, number of packets not analyzed and not dumped

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).