android/media/MediaDescrambler.java

/*
 * Copyright (C) 2017 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 android.media;

import android.annotation.NonNull;
import android.hardware.cas.V1_0.*;
import android.media.MediaCasException.UnsupportedCasException;
import android.os.IHwBinder;
import android.os.RemoteException;
import android.os.ServiceSpecificException;
import android.util.Log;

import java.nio.ByteBuffer;

/**
 * MediaDescrambler class can be used in conjunction with {@link android.media.MediaCodec}
 * and {@link android.media.MediaExtractor} to decode media data scrambled by conditional
 * access (CA) systems such as those in the ISO/IEC13818-1.
 *
 * A MediaDescrambler object is initialized from a session opened by a MediaCas object,
 * and can be used to descramble media streams scrambled with that session's keys.
 *
 * Scrambling schemes are identified by 16-bit unsigned integer as in CA_system_id.
 *
 */
public final class MediaDescrambler implements AutoCloseable {
    private static final String TAG = "MediaDescrambler";
    private IDescramblerBase mIDescrambler;

    private final void validateInternalStates() {
        if (mIDescrambler == null) {
            throw new IllegalStateException();
        }
    }

    private final void cleanupAndRethrowIllegalState() {
        mIDescrambler = null;
        throw new IllegalStateException();
    }

    /**
     * Instantiate a MediaDescrambler.
     *
     * @param CA_system_id The system id of the scrambling scheme.
     *
     * @throws UnsupportedCasException if the scrambling scheme is not supported.
     */
    public MediaDescrambler(int CA_system_id) throws UnsupportedCasException {
        try {
            mIDescrambler = MediaCas.getService().createDescrambler(CA_system_id);
        } catch(Exception e) {
            Log.e(TAG, "Failed to create descrambler: " + e);
            mIDescrambler = null;
        } finally {
            if (mIDescrambler == null) {
                throw new UnsupportedCasException("Unsupported CA_system_id " + CA_system_id);
            }
        }
        native_setup(mIDescrambler.asBinder());
    }

    IHwBinder getBinder() {
        validateInternalStates();

        return mIDescrambler.asBinder();
    }

    /**
     * Query if the scrambling scheme requires the use of a secure decoder
     * to decode data of the given mime type.
     *
     * @param mime The mime type of the media data
     *
     * @throws IllegalStateException if the descrambler instance is not valid.
     */
    public final boolean requiresSecureDecoderComponent(@NonNull String mime) {
        validateInternalStates();

        try {
            return mIDescrambler.requiresSecureDecoderComponent(mime);
        } catch (RemoteException e) {
            cleanupAndRethrowIllegalState();
        }
        return true;
    }

    /**
     * Associate a MediaCas session with this MediaDescrambler instance.
     * The MediaCas session is used to securely load decryption keys for
     * the descrambler. The crypto keys loaded through the MediaCas session
     * may be selected for use during the descrambling operation performed
     * by {@link android.media.MediaExtractor or @link
     * android.media.MediaCodec#queueSecureInputBuffer} by specifying even
     * or odd key in the {@link android.media.MediaCodec.CryptoInfo#key} field.
     *
     * @param session the MediaCas session to associate with this
     * MediaDescrambler instance.
     *
     * @throws IllegalStateException if the descrambler instance is not valid.
     * @throws MediaCasStateException for CAS-specific state exceptions.
     */
    public final void setMediaCasSession(@NonNull MediaCas.Session session) {
        validateInternalStates();

        try {
            MediaCasStateException.throwExceptionIfNeeded(
                    mIDescrambler.setMediaCasSession(session.mSessionId));
        } catch (RemoteException e) {
            cleanupAndRethrowIllegalState();
        }
    }

    /**
     * Scramble control value indicating that the samples are not scrambled.
     * @see #descramble(ByteBuffer, ByteBuffer, android.media.MediaCodec.CryptoInfo)
     */
    public static final byte SCRAMBLE_CONTROL_UNSCRAMBLED = 0;

    /**
     * Scramble control value reserved and shouldn't be used currently.
     * @see #descramble(ByteBuffer, ByteBuffer, android.media.MediaCodec.CryptoInfo)
     */
    public static final byte SCRAMBLE_CONTROL_RESERVED    = 1;

    /**
     * Scramble control value indicating that the even key is used.
     * @see #descramble(ByteBuffer, ByteBuffer, android.media.MediaCodec.CryptoInfo)
     */
    public static final byte SCRAMBLE_CONTROL_EVEN_KEY     = 2;

    /**
     * Scramble control value indicating that the odd key is used.
     * @see #descramble(ByteBuffer, ByteBuffer, android.media.MediaCodec.CryptoInfo)
     */
    public static final byte SCRAMBLE_CONTROL_ODD_KEY      = 3;

    /**
     * Scramble flag for a hint indicating that the descrambling request is for
     * retrieving the PES header info only.
     *
     * @see #descramble(ByteBuffer, ByteBuffer, android.media.MediaCodec.CryptoInfo)
     */
    public static final byte SCRAMBLE_FLAG_PES_HEADER = (1 << 0);

    /**
     * Descramble a ByteBuffer of data described by a
     * {@link android.media.MediaCodec.CryptoInfo} structure.
     *
     * @param srcBuf ByteBuffer containing the scrambled data, which starts at
     * srcBuf.position().
     * @param dstBuf ByteBuffer to hold the descrambled data, which starts at
     * dstBuf.position().
     * @param cryptoInfo a {@link android.media.MediaCodec.CryptoInfo} structure
     * describing the subsamples contained in srcBuf. The iv and mode fields in
     * CryptoInfo are not used. key[0] contains the MPEG2TS scrambling control bits
     * (as defined in ETSI TS 100 289 (2011): "Digital Video Broadcasting (DVB);
     * Support for use of the DVB Scrambling Algorithm version 3 within digital
     * broadcasting systems"), and the value must be one of {@link #SCRAMBLE_CONTROL_UNSCRAMBLED},
     * {@link #SCRAMBLE_CONTROL_RESERVED}, {@link #SCRAMBLE_CONTROL_EVEN_KEY} or
     * {@link #SCRAMBLE_CONTROL_ODD_KEY}. key[1] is a set of bit flags, with the
     * only possible bit being {@link #SCRAMBLE_FLAG_PES_HEADER} currently.
     * key[2~15] are not used.
     *
     * @return number of bytes that have been successfully descrambled, with negative
     * values indicating errors.
     *
     * @throws IllegalStateException if the descrambler instance is not valid.
     * @throws MediaCasStateException for CAS-specific state exceptions.
     */
    public final int descramble(
            @NonNull ByteBuffer srcBuf, @NonNull ByteBuffer dstBuf,
            @NonNull MediaCodec.CryptoInfo cryptoInfo) {
        validateInternalStates();

        if (cryptoInfo.numSubSamples <= 0) {
            throw new IllegalArgumentException(
                    "Invalid CryptoInfo: invalid numSubSamples=" + cryptoInfo.numSubSamples);
        } else if (cryptoInfo.numBytesOfClearData == null
                && cryptoInfo.numBytesOfEncryptedData == null) {
            throw new IllegalArgumentException(
                    "Invalid CryptoInfo: clearData and encryptedData size arrays are both null!");
        } else if (cryptoInfo.numBytesOfClearData != null
                && cryptoInfo.numBytesOfClearData.length < cryptoInfo.numSubSamples) {
            throw new IllegalArgumentException(
                    "Invalid CryptoInfo: numBytesOfClearData is too small!");
        } else if (cryptoInfo.numBytesOfEncryptedData != null
                && cryptoInfo.numBytesOfEncryptedData.length < cryptoInfo.numSubSamples) {
            throw new IllegalArgumentException(
                    "Invalid CryptoInfo: numBytesOfEncryptedData is too small!");
        } else if (cryptoInfo.key == null || cryptoInfo.key.length != 16) {
            throw new IllegalArgumentException(
                    "Invalid CryptoInfo: key array is invalid!");
        }

        try {
            return native_descramble(
                    cryptoInfo.key[0],
                    cryptoInfo.key[1],
                    cryptoInfo.numSubSamples,
                    cryptoInfo.numBytesOfClearData,
                    cryptoInfo.numBytesOfEncryptedData,
                    srcBuf, srcBuf.position(), srcBuf.limit(),
                    dstBuf, dstBuf.position(), dstBuf.limit());
        } catch (ServiceSpecificException e) {
            MediaCasStateException.throwExceptionIfNeeded(e.errorCode, e.getMessage());
        } catch (RemoteException e) {
            cleanupAndRethrowIllegalState();
        }
        return -1;
    }

    @Override
    public void close() {
        if (mIDescrambler != null) {
            try {
                mIDescrambler.release();
            } catch (RemoteException e) {
            } finally {
                mIDescrambler = null;
            }
        }
        native_release();
    }

    @Override
    protected void finalize() {
        close();
    }

    private static native final void native_init();
    private native final void native_setup(@NonNull IHwBinder decramblerBinder);
    private native final void native_release();
    private native final int native_descramble(
            byte key, byte flags, int numSubSamples,
            int[] numBytesOfClearData, int[] numBytesOfEncryptedData,
            @NonNull ByteBuffer srcBuf, int srcOffset, int srcLimit,
            ByteBuffer dstBuf, int dstOffset, int dstLimit) throws RemoteException;

    static {
        System.loadLibrary("media_jni");
        native_init();
    }

    private long mNativeContext;
}