src/com/android/remoteprovisioner/WidevineProvisioner.java

/**
 * Copyright (C) 2022 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.remoteprovisioner;

import android.content.Context;
import android.media.DeniedByServerException;
import android.media.MediaDrm;
import android.media.UnsupportedSchemeException;
import android.util.Log;

import androidx.annotation.NonNull;
import androidx.work.Worker;
import androidx.work.WorkerParameters;

import java.io.BufferedInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.HashMap;
import java.util.Map;
import java.util.UUID;

/**
 * Provides the functionality necessary to provision a Widevine instance running Provisioning 4.0.
 * This class extends the Worker class so that it can be scheduled as a one time work request
 * in the BootReceiver if the device does need to be provisioned. This can technically be handled
 * by any application, but is done within this application for convenience purposes.
 */
public class WidevineProvisioner extends Worker {

    private static final int MAX_RETRIES = 3;
    private static final int TIMEOUT_MS = 20000;

    private static final String TAG = "RemoteProvisioningWV";

    private static final byte[] EMPTY_BODY = new byte[0];

    private static final Map<String, String> REQ_PROPERTIES = new HashMap<String, String>();
    static {
        REQ_PROPERTIES.put("Accept", "*/*");
        REQ_PROPERTIES.put("User-Agent", "Widevine CDM v1.0");
        REQ_PROPERTIES.put("Content-Type", "application/json");
        REQ_PROPERTIES.put("Connection", "close");
    }

    public static final UUID WIDEVINE_UUID = new UUID(0xEDEF8BA979D64ACEL, 0xA3C827DCD51D21EDL);

    public WidevineProvisioner(@NonNull Context context, @NonNull WorkerParameters params) {
        super(context, params);
    }

    private Result retryOrFail() {
        if (getRunAttemptCount() < MAX_RETRIES) {
            return Result.retry();
        } else {
            return Result.failure();
        }
    }

    /**
     * Overrides the default doWork method to handle checking and provisioning the device's
     * widevine certificate.
     */
    @Override
    public Result doWork() {
        Log.i(TAG, "Beginning WV provisioning request. Current attempt: " + getRunAttemptCount());
        return provisionWidevine();
    }

    /**
     * Checks the status of the system in order to determine if stage 1 certificate provisioning
     * for Provisioning 4.0 needs to be performed.
     *
     * @return true if the device supports Provisioning 4.0 and the system ID indicates it has not
     *         yet been provisioned.
     */
    public static boolean isWidevineProvisioningNeeded() {
        try {
            final MediaDrm drm = new MediaDrm(WidevineProvisioner.WIDEVINE_UUID);

            if (!drm.getPropertyString("provisioningModel").equals("BootCertificateChain")) {
                // Not a provisioning 4.0 device.
                Log.i(TAG, "Not a WV provisioning 4.0 device. No provisioning required.");
                return false;
            }
            int systemId = Integer.parseInt(drm.getPropertyString("systemId"));
            if (systemId != Integer.MAX_VALUE) {
                Log.i(TAG, "This device has already been provisioned with its WV cert.");
                // First stage provisioning probably complete
                return false;
            }
            return true;
        } catch (UnsupportedSchemeException e) {
            // Suppress the exception. It isn't particularly informative and may confuse anyone
            // reading the logs.
            Log.i(TAG, "Widevine not supported. No need to provision widevine certificates.");
            return false;
        } catch (Exception e) {
            Log.e(TAG, "Something went wrong. Will not provision widevine certificates.", e);
            return false;
        }
    }

    /**
     * Performs the full roundtrip necessary to provision widevine with the first stage cert
     * in Provisioning 4.0.
     *
     * @return A Result indicating whether the attempt succeeded, failed, or should be retried.
     */
    public Result provisionWidevine() {
        try {
            final MediaDrm drm = new MediaDrm(WIDEVINE_UUID);
            final MediaDrm.ProvisionRequest request = drm.getProvisionRequest();
            drm.provideProvisionResponse(fetchWidevineCertificate(request));
        } catch (UnsupportedSchemeException e) {
            Log.e(TAG, "WV provisioning unsupported. Should not have been able to get here.", e);
            return Result.success();
        } catch (DeniedByServerException e) {
            Log.e(TAG, "WV server denied the provisioning request.", e);
            return Result.failure();
        } catch (IOException e) {
            Log.e(TAG, "WV Provisioning failed.", e);
            return retryOrFail();
        } catch (Exception e) {
            Log.e(TAG, "Safety catch-all in case of an unexpected run time exception:", e);
            return retryOrFail();
        }
        Log.i(TAG, "Provisioning successful.");
        return Result.success();
    }

    private byte[] fetchWidevineCertificate(MediaDrm.ProvisionRequest req) throws IOException {
        final byte[] data = req.getData();
        final String signedUrl = String.format(
                "%s&signedRequest=%s",
                req.getDefaultUrl(),
                new String(data));
        return sendNetworkRequest(signedUrl);
    }

    private byte[] sendNetworkRequest(String url) throws IOException {
        HttpURLConnection con = (HttpURLConnection) new URL(url).openConnection();
        con.setRequestMethod("POST");
        con.setDoOutput(true);
        con.setDoInput(true);
        con.setConnectTimeout(TIMEOUT_MS);
        con.setReadTimeout(TIMEOUT_MS);
        con.setChunkedStreamingMode(0);
        for (Map.Entry<String, String> prop : REQ_PROPERTIES.entrySet()) {
            con.setRequestProperty(prop.getKey(), prop.getValue());
        }

        try (OutputStream os = con.getOutputStream()) {
            os.write(EMPTY_BODY);
        }
        if (con.getResponseCode() != 200) {
            Log.e(TAG, "Server request for WV certs failed. Error: " + con.getResponseCode());
            throw new IOException("Failed to request WV certs. Error: " + con.getResponseCode());
        }

        BufferedInputStream inputStream = new BufferedInputStream(con.getInputStream());
        ByteArrayOutputStream respBytes = new ByteArrayOutputStream();
        byte[] buffer = new byte[1024];
        int read = 0;
        while ((read = inputStream.read(buffer, 0, buffer.length)) != -1) {
            respBytes.write(buffer, 0, read);
        }
        byte[] respData = respBytes.toByteArray();
        if (respData.length == 0) {
            Log.e(TAG, "WV server returned an empty response.");
            throw new IOException("WV server returned an empty response.");
        }
        return respData;
    }
}