src/net/lightstone/util/nbt/NBTInputStream.java

package net.lightstone.util.nbt;

import java.io.Closeable;
import java.io.DataInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.zip.GZIPInputStream;

/**
 * This class reads NBT, or Named Binary Tag streams, and produces an object
 * graph of subclasses of the {@link Tag} object.
 * <p />
 * The NBT format was created by Markus Persson, and the specification may
 * be found at <a href="http://www.minecraft.net/docs/NBT.txt">
 * http://www.minecraft.net/docs/NBT.txt</a>.
 * @author Graham Edgecombe
 */
public final class NBTInputStream implements Closeable {

	/**
	 * The data input stream.
	 */
	private final DataInputStream is;

	/**
	 * Creates a new {@link NBTInputStream}, which will source its data
	 * from the specified input stream. This assumes the stream is compressed.
	 * @param is The input stream.
	 * @throws IOException if an I/O error occurs.
	 */
	public NBTInputStream(InputStream is) throws IOException {
		this(is, true);
	}

	/**
	 * Creates a new {@link NBTInputStream}, which sources its data from the
	 * specified input stream. A flag must be passed which indicates if the
	 * stream is compressed with GZIP or not.
	 * @param is The input stream.
	 * @param compressed A flag indicating if the stream is compressed.
	 * @throws IOException if an I/O error occurs.
	 */
	public NBTInputStream(InputStream is, boolean compressed) throws IOException {
		this.is = new DataInputStream(compressed ? new GZIPInputStream(is) : is);
	}

	/**
	 * Reads an NBT {@link Tag} from the stream.
	 * @return The tag that was read.
	 * @throws IOException if an I/O error occurs.
	 */
	public Tag readTag() throws IOException {
		return readTag(0);
	}

	/**
	 * Reads an NBT {@link Tag} from the stream.
	 * @param depth The depth of this tag.
	 * @return The tag that was read.
	 * @throws IOException if an I/O error occurs.
	 */
	private Tag readTag(int depth) throws IOException {
		int type = is.readByte() & 0xFF;

		String name;
		if (type != NBTConstants.TYPE_END) {
			int nameLength = is.readShort() & 0xFFFF;
			byte[] nameBytes = new byte[nameLength];
			is.readFully(nameBytes);
			name = new String(nameBytes, NBTConstants.CHARSET);
		} else {
			name = "";
		}

		return readTagPayload(type, name, depth);
	}

	/**
	 * Reads the payload of a {@link Tag}, given the name and type.
	 * @param type The type.
	 * @param name The name.
	 * @param depth The depth.
	 * @return The tag.
	 * @throws IOException if an I/O error occurs.
	 */
	@SuppressWarnings("unchecked")
	private Tag readTagPayload(int type, String name, int depth) throws IOException {
		switch (type) {
		case NBTConstants.TYPE_END:
			if (depth == 0) {
				throw new IOException("TAG_End found without a TAG_Compound/TAG_List tag preceding it.");
			} else {
				return new EndTag();
			}

		case NBTConstants.TYPE_BYTE:
			return new ByteTag(name, is.readByte());

		case NBTConstants.TYPE_SHORT:
			return new ShortTag(name, is.readShort());

		case NBTConstants.TYPE_INT:
			return new IntTag(name, is.readInt());

		case NBTConstants.TYPE_LONG:
			return new LongTag(name, is.readLong());

		case NBTConstants.TYPE_FLOAT:
			return new FloatTag(name, is.readFloat());

		case NBTConstants.TYPE_DOUBLE:
			return new DoubleTag(name, is.readDouble());

		case NBTConstants.TYPE_BYTE_ARRAY:
			int length = is.readInt();
			byte[] bytes = new byte[length];
			is.readFully(bytes);
			return new ByteArrayTag(name, bytes);

		case NBTConstants.TYPE_STRING:
			length = is.readShort();
			bytes = new byte[length];
			is.readFully(bytes);
			return new StringTag(name, new String(bytes, NBTConstants.CHARSET));

		case NBTConstants.TYPE_LIST:
			int childType = is.readByte();
			length = is.readInt();

			Class<? extends Tag> clazz = NBTUtils.getTypeClass(childType);
			List<Tag> tagList = new ArrayList<Tag>();
			for (int i = 0; i < length; i++) {
				Tag tag = readTagPayload(childType, "", depth + 1);
				if (tag instanceof EndTag) {
					throw new IOException("TAG_End not permitted in a list.");
				} else if (!clazz.isInstance(tag)) {
					throw new IOException("Mixed tag types within a list.");
				}
				tagList.add(tag);
			}

			return new ListTag(name, clazz, tagList);

		case NBTConstants.TYPE_COMPOUND:
			Map<String, Tag> tagMap = new HashMap<String, Tag>();
			while (true) {
				Tag tag = readTag(depth + 1);
				if(tag instanceof EndTag) {
					break;
				} else {
					tagMap.put(tag.getName(), tag);
				}
			}

			return new CompoundTag(name, tagMap);

		default:
			throw new IOException("Invalid tag type: " + type + ".");
		}
	}

	@Override
	public void close() throws IOException {
		is.close();
	}

}