content/res/AssetFileDescriptor.java

/*
 * Copyright (C) 2006 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.content.res;

import android.os.MemoryFile;
import android.os.Parcel;
import android.os.ParcelFileDescriptor;
import android.os.Parcelable;

import java.io.FileDescriptor;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.nio.channels.FileChannel;

/**
 * File descriptor of an entry in the AssetManager.  This provides your own
 * opened FileDescriptor that can be used to read the data, as well as the
 * offset and length of that entry's data in the file.
 */
public class AssetFileDescriptor implements Parcelable {
    /**
     * Length used with {@link #AssetFileDescriptor(ParcelFileDescriptor, long, long)}
     * and {@link #getDeclaredLength} when a length has not been declared.  This means
     * the data extends to the end of the file.
     */
    public static final long UNKNOWN_LENGTH = -1;

    private final ParcelFileDescriptor mFd;
    private final long mStartOffset;
    private final long mLength;

    /**
     * Create a new AssetFileDescriptor from the given values.
     * @param fd The underlying file descriptor.
     * @param startOffset The location within the file that the asset starts.
     * This must be 0 if length is UNKNOWN_LENGTH.
     * @param length The number of bytes of the asset, or
     * {@link #UNKNOWN_LENGTH if it extends to the end of the file.
     */
    public AssetFileDescriptor(ParcelFileDescriptor fd, long startOffset,
            long length) {
        if (length < 0 && startOffset != 0) {
            throw new IllegalArgumentException(
                    "startOffset must be 0 when using UNKNOWN_LENGTH");
        }
        mFd = fd;
        mStartOffset = startOffset;
        mLength = length;
    }

    /**
     * The AssetFileDescriptor contains its own ParcelFileDescriptor, which
     * in addition to the normal FileDescriptor object also allows you to close
     * the descriptor when you are done with it.
     */
    public ParcelFileDescriptor getParcelFileDescriptor() {
        return mFd;
    }

    /**
     * Returns the FileDescriptor that can be used to read the data in the
     * file.
     */
    public FileDescriptor getFileDescriptor() {
        return mFd.getFileDescriptor();
    }

    /**
     * Returns the byte offset where this asset entry's data starts.
     */
    public long getStartOffset() {
        return mStartOffset;
    }

    /**
     * Returns the total number of bytes of this asset entry's data.  May be
     * {@link #UNKNOWN_LENGTH} if the asset extends to the end of the file.
     * If the AssetFileDescriptor was constructed with {@link #UNKNOWN_LENGTH},
     * this will use {@link ParcelFileDescriptor#getStatSize()
     * ParcelFileDescriptor.getStatSize()} to find the total size of the file,
     * returning that number if found or {@link #UNKNOWN_LENGTH} if it could
     * not be determined.
     *
     * @see #getDeclaredLength()
     */
    public long getLength() {
        if (mLength >= 0) {
            return mLength;
        }
        long len = mFd.getStatSize();
        return len >= 0 ? len : UNKNOWN_LENGTH;
    }

    /**
     * Return the actual number of bytes that were declared when the
     * AssetFileDescriptor was constructed.  Will be
     * {@link #UNKNOWN_LENGTH} if the length was not declared, meaning data
     * should be read to the end of the file.
     *
     * @see #getDeclaredLength()
     */
    public long getDeclaredLength() {
        return mLength;
    }

    /**
     * Convenience for calling <code>getParcelFileDescriptor().close()</code>.
     */
    public void close() throws IOException {
        mFd.close();
    }

    /**
     * Checks whether this file descriptor is for a memory file.
     */
    private boolean isMemoryFile() {
        try {
            return MemoryFile.isMemoryFile(mFd.getFileDescriptor());
        } catch (IOException e) {
            return false;
        }
    }

    /**
     * Create and return a new auto-close input stream for this asset.  This
     * will either return a full asset {@link AutoCloseInputStream}, or
     * an underlying {@link ParcelFileDescriptor.AutoCloseInputStream
     * ParcelFileDescriptor.AutoCloseInputStream} depending on whether the
     * the object represents a complete file or sub-section of a file.  You
     * should only call this once for a particular asset.
     */
    public FileInputStream createInputStream() throws IOException {
        if (isMemoryFile()) {
            if (mLength > Integer.MAX_VALUE) {
                throw new IOException("File length too large for a memory file: " + mLength);
            }
            return new AutoCloseMemoryFileInputStream(mFd, (int)mLength);
        }
        if (mLength < 0) {
            return new ParcelFileDescriptor.AutoCloseInputStream(mFd);
        }
        return new AutoCloseInputStream(this);
    }

    /**
     * Create and return a new auto-close output stream for this asset.  This
     * will either return a full asset {@link AutoCloseOutputStream}, or
     * an underlying {@link ParcelFileDescriptor.AutoCloseOutputStream
     * ParcelFileDescriptor.AutoCloseOutputStream} depending on whether the
     * the object represents a complete file or sub-section of a file.  You
     * should only call this once for a particular asset.
     */
    public FileOutputStream createOutputStream() throws IOException {
        if (mLength < 0) {
            return new ParcelFileDescriptor.AutoCloseOutputStream(mFd);
        }
        return new AutoCloseOutputStream(this);
    }

    @Override
    public String toString() {
        return "{AssetFileDescriptor: " + mFd
                + " start=" + mStartOffset + " len=" + mLength + "}";
    }

    /**
     * An InputStream you can create on a ParcelFileDescriptor, which will
     * take care of calling {@link ParcelFileDescriptor#close
     * ParcelFileDescritor.close()} for you when the stream is closed.
     */
    public static class AutoCloseInputStream
            extends ParcelFileDescriptor.AutoCloseInputStream {
        private long mRemaining;

        public AutoCloseInputStream(AssetFileDescriptor fd) throws IOException {
            super(fd.getParcelFileDescriptor());
            super.skip(fd.getStartOffset());
            mRemaining = (int)fd.getLength();
        }

        @Override
        public int available() throws IOException {
            return mRemaining >= 0
                    ? (mRemaining < 0x7fffffff ? (int)mRemaining : 0x7fffffff)
                    : super.available();
        }

        @Override
        public int read() throws IOException {
            if (mRemaining >= 0) {
                if (mRemaining == 0) return -1;
                int res = super.read();
                if (res >= 0) mRemaining--;
                return res;
            }

            return super.read();
        }

        @Override
        public int read(byte[] buffer, int offset, int count) throws IOException {
            if (mRemaining >= 0) {
                if (mRemaining == 0) return -1;
                if (count > mRemaining) count = (int)mRemaining;
                int res = super.read(buffer, offset, count);
                if (res >= 0) mRemaining -= res;
                return res;
            }

            return super.read(buffer, offset, count);
        }

        @Override
        public int read(byte[] buffer) throws IOException {
            if (mRemaining >= 0) {
                if (mRemaining == 0) return -1;
                int count = buffer.length;
                if (count > mRemaining) count = (int)mRemaining;
                int res = super.read(buffer, 0, count);
                if (res >= 0) mRemaining -= res;
                return res;
            }

            return super.read(buffer);
        }

        @Override
        public long skip(long count) throws IOException {
            if (mRemaining >= 0) {
                if (mRemaining == 0) return -1;
                if (count > mRemaining) count = mRemaining;
                long res = super.skip(count);
                if (res >= 0) mRemaining -= res;
                return res;
            }

            // TODO Auto-generated method stub
            return super.skip(count);
        }

        @Override
        public void mark(int readlimit) {
            if (mRemaining >= 0) {
                // Not supported.
                return;
            }
            super.mark(readlimit);
        }

        @Override
        public boolean markSupported() {
            if (mRemaining >= 0) {
                return false;
            }
            return super.markSupported();
        }

        @Override
        public synchronized void reset() throws IOException {
            if (mRemaining >= 0) {
                // Not supported.
                return;
            }
            super.reset();
        }
    }

    /**
     * An input stream that reads from a MemoryFile and closes it when the stream is closed.
     * This extends FileInputStream just because {@link #createInputStream} returns
     * a FileInputStream. All the FileInputStream methods are
     * overridden to use the MemoryFile instead.
     */
    private static class AutoCloseMemoryFileInputStream extends FileInputStream {
        private ParcelFileDescriptor mParcelFd;
        private MemoryFile mFile;
        private InputStream mStream;

        public AutoCloseMemoryFileInputStream(ParcelFileDescriptor fd, int length)
                throws IOException {
            super(fd.getFileDescriptor());
            mParcelFd = fd;
            mFile = new MemoryFile(fd.getFileDescriptor(), length, "r");
            mStream = mFile.getInputStream();
        }

        @Override
        public int available() throws IOException {
            return mStream.available();
        }

        @Override
        public void close() throws IOException {
            mParcelFd.close();  // must close ParcelFileDescriptor, not just the file descriptor,
                                // since it could be a subclass of ParcelFileDescriptor.
                                // E.g. ContentResolver.ParcelFileDescriptorInner.close() releases
                                // a content provider
            mFile.close();      // to unmap the memory file from the address space.
            mStream.close();    // doesn't actually do anything
        }

        @Override
        public FileChannel getChannel() {
            return null;
        }

        @Override
        public int read() throws IOException {
            return mStream.read();
        }

        @Override
        public int read(byte[] buffer, int offset, int count) throws IOException {
            return mStream.read(buffer, offset, count);
        }

        @Override
        public int read(byte[] buffer) throws IOException {
            return mStream.read(buffer);
        }

        @Override
        public long skip(long count) throws IOException {
            return mStream.skip(count);
        }
    }

    /**
     * An OutputStream you can create on a ParcelFileDescriptor, which will
     * take care of calling {@link ParcelFileDescriptor#close
     * ParcelFileDescritor.close()} for you when the stream is closed.
     */
    public static class AutoCloseOutputStream
            extends ParcelFileDescriptor.AutoCloseOutputStream {
        private long mRemaining;

        public AutoCloseOutputStream(AssetFileDescriptor fd) throws IOException {
            super(fd.getParcelFileDescriptor());
            if (fd.getParcelFileDescriptor().seekTo(fd.getStartOffset()) < 0) {
                throw new IOException("Unable to seek");
            }
            mRemaining = (int)fd.getLength();
        }

        @Override
        public void write(byte[] buffer, int offset, int count) throws IOException {
            if (mRemaining >= 0) {
                if (mRemaining == 0) return;
                if (count > mRemaining) count = (int)mRemaining;
                super.write(buffer, offset, count);
                mRemaining -= count;
                return;
            }

            super.write(buffer, offset, count);
        }

        @Override
        public void write(byte[] buffer) throws IOException {
            if (mRemaining >= 0) {
                if (mRemaining == 0) return;
                int count = buffer.length;
                if (count > mRemaining) count = (int)mRemaining;
                super.write(buffer);
                mRemaining -= count;
                return;
            }

            super.write(buffer);
        }

        @Override
        public void write(int oneByte) throws IOException {
            if (mRemaining >= 0) {
                if (mRemaining == 0) return;
                super.write(oneByte);
                mRemaining--;
                return;
            }

            super.write(oneByte);
        }
    }


    /* Parcelable interface */
    public int describeContents() {
        return mFd.describeContents();
    }

    public void writeToParcel(Parcel out, int flags) {
        mFd.writeToParcel(out, flags);
        out.writeLong(mStartOffset);
        out.writeLong(mLength);
    }

    AssetFileDescriptor(Parcel src) {
        mFd = ParcelFileDescriptor.CREATOR.createFromParcel(src);
        mStartOffset = src.readLong();
        mLength = src.readLong();
    }

    public static final Parcelable.Creator<AssetFileDescriptor> CREATOR
            = new Parcelable.Creator<AssetFileDescriptor>() {
        public AssetFileDescriptor createFromParcel(Parcel in) {
            return new AssetFileDescriptor(in);
        }
        public AssetFileDescriptor[] newArray(int size) {
            return new AssetFileDescriptor[size];
        }
    };

    /**
     * Creates an AssetFileDescriptor from a memory file.
     *
     * @hide
     */
    public static AssetFileDescriptor fromMemoryFile(MemoryFile memoryFile)
            throws IOException {
        ParcelFileDescriptor fd = memoryFile.getParcelFileDescriptor();
        return new AssetFileDescriptor(fd, 0, memoryFile.length());
    }

}