RRDFile.java

package org.rrd4j.core.jrrd;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;

/**
 * This class is used read information from an RRD file. Writing
 * to RRD files is not currently supported. It uses NIO's RandomAccessFile to read the file
 * <p/>
 * Currently this can read RRD files that were generated on Solaris (Sparc)
 * and Linux (x86).
 *
 * @author <a href="mailto:ciaran@codeloop.com">Ciaran Treanor</a>
 * @version $Revision: 1.1 $
 */
class RRDFile implements Constants {
    private int alignment;
    private int longSize = 4;

    private final FileInputStream underlying;
    private final MappedByteBuffer mappedByteBuffer;

    private ByteOrder order;

    RRDFile(String name) throws IOException {
        this(new File(name));
    }

    RRDFile(File file) throws IOException {
        long len = file.length();
        if (len > Integer.MAX_VALUE) {
            throw new IllegalArgumentException(
                    "RRDFile cannot read files larger than 2**31 because of limitations of java.nio.ByteBuffer");
        }

        boolean ok = false;
        try {
            underlying = new FileInputStream(file);
            mappedByteBuffer = underlying.getChannel().map(FileChannel.MapMode.READ_ONLY, 0, len);
            initDataLayout(file);
            ok = true;
        } finally {
            if (!ok) {
                try {
                    close();
                } catch (Throwable ignored) {
                }
                // and then rethrow
            }
        }
    }

    private void initDataLayout(File file) throws IOException {

        if (file.exists()) {    // Load the data formats from the file
            byte[] buffer = new byte[32];
            mappedByteBuffer.get(buffer);
            ByteBuffer bbuffer = ByteBuffer.wrap(buffer);

            int index;

            if ((index = indexOf(FLOAT_COOKIE_BIG_ENDIAN, buffer)) != -1) {
                order = ByteOrder.BIG_ENDIAN;
            }
            else if ((index = indexOf(FLOAT_COOKIE_LITTLE_ENDIAN, buffer))
                    != -1) {
                order = ByteOrder.LITTLE_ENDIAN;
            }
            else {
                throw new IOException("Invalid RRD file");
            }
            mappedByteBuffer.order(order);
            bbuffer.order(order);

            switch (index) {

            case 12:
                alignment = 4;
                break;

            case 16:
                alignment = 8;
                break;

            default:
                throw new RuntimeException("Unsupported architecture");
            }

            bbuffer.position(index + 8);
            //We cannot have dsCount && rracount == 0
            //If one is 0, it's a 64 bits rrd
            int int1 = bbuffer.getInt();  //Should be dsCount in ILP32
            int int2 = bbuffer.getInt();  //Should be rraCount in ILP32
            if(int1  == 0 || int2 ==0) {
                longSize = 8;
            }
        }
        else {                // Default to data formats for this hardware architecture
        }
        // Reset file pointer to start of file
        mappedByteBuffer.rewind();
    }

    private int indexOf(byte[] pattern, byte[] array) {
        return (new String(array)).indexOf(new String(pattern));
    }

    boolean isBigEndian() {
        return order == ByteOrder.BIG_ENDIAN;
    }

    int getAlignment() {
        return alignment;
    }

    double readDouble() throws IOException {
        return mappedByteBuffer.getDouble();
    }

    int readInt() throws IOException {
        return mappedByteBuffer.getInt();
    }

    int readLong() throws IOException {
        if(longSize == 4) {
            return mappedByteBuffer.getInt();
        }
        else {
            return (int) mappedByteBuffer.getLong();
        }
    }

    String readString(int maxLength) throws IOException {
        byte[] array = new byte[maxLength];
        mappedByteBuffer.get(array);

        return new String(array, 0, maxLength).trim();
    }

    void skipBytes(int n) throws IOException {
        mappedByteBuffer.position(mappedByteBuffer.position() + n);
    }

    int align(int boundary) throws IOException {

        int skip = (int) (boundary - (mappedByteBuffer.position() % boundary)) % boundary;

        if (skip != 0) {
            mappedByteBuffer.position(mappedByteBuffer.position() + skip);
        }

        return skip;
    }

    int align() throws IOException {
        return align(alignment);
    }

    long info() throws IOException {
        return mappedByteBuffer.position();
    }

    long getFilePointer() throws IOException {
        return mappedByteBuffer.position();
    }

    void close() throws IOException {
        if (underlying != null) {
            underlying.close();
        }
    }

    void read(ByteBuffer bb) throws IOException{
        int count = bb.remaining();
        bb.put((ByteBuffer) mappedByteBuffer.duplicate().limit(mappedByteBuffer.position() + count));
        mappedByteBuffer.position(mappedByteBuffer.position() + count);
    }

    UnivalArray getUnivalArray(int size) throws IOException {
        return new UnivalArray(this, size);
    }

    /**
     * @return the long size in bits for this file
     */
    int getBits() {
        return longSize * 8;
    }

    public void seek(long position) {
        mappedByteBuffer.position((int) position);
    }

    public void seekToEndOfFile() {
        mappedByteBuffer.position(mappedByteBuffer.limit());
    }
}