net.lenni0451.mcping.stream.MCInputStream Maven / Gradle / Ivy

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A simple library to ping minecraft servers
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package net.lenni0451.mcping.stream;

import net.lenni0451.mcping.exception.DataReadException;
import net.lenni0451.mcping.pings.impl.ClassicPing;

import java.io.DataInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.nio.charset.StandardCharsets;

/**
 * A data input stream which can read minecraft specific data types.
 * Implemented types:
 * - var int
 * - var string
 * - legacy string
 * - classic string
 */
public class MCInputStream extends DataInputStream {

    public MCInputStream(final InputStream is) {
        super(is);
    }

    /**
     * Read a var int from the stream.
     *
     * @return The read var int
     * @throws IOException       If an I/O error occurs
     * @throws DataReadException If the var int is too big
     */
    public int readVarInt() throws IOException {
        int i = 0;
        int j = 0;

        byte b;
        do {
            b = this.readByte();
            i |= (b & 127) << j++ * 7;
            if (j > 5) throw new DataReadException("Var int too big");
        } while ((b & 128) == 128);

        return i;
    }

    /**
     * Read a var string from the stream.

     * This is the string format used by the modern ping protocol ({@literal >}= 1.7).
     *
     * @param maxLength The maximum length of the string
     * @return The read string
     * @throws IOException       If an I/O error occurs
     * @throws DataReadException If the string length is invalid
     */
    public String readVarString(final int maxLength) throws IOException {
        int length = this.readVarInt();
        if (length > maxLength * 4) throw new DataReadException("Encoded string buffer is larger than allowed (" + length + " > " + (maxLength * 4) + ")");
        if (length < 0) throw new DataReadException("Encoded string buffer is smaller than allowed (" + length + " < 0)");

        byte[] bytes = new byte[length];
        this.readFully(bytes);
        String string = new String(bytes, StandardCharsets.UTF_8);
        if (string.length() > maxLength) throw new DataReadException("String is longer than allowed (" + length + " > " + maxLength + ")");
        else return string;
    }

    /**
     * Read a legacy string from the stream.

     * This is the string format used by the old ping protocol ({@literal <}= 1.6).
     *
     * @return The read string
     * @throws IOException       If an I/O error occurs
     * @throws DataReadException If the string length is invalid
     */
    public String readLegacyString() throws IOException {
        int length = this.readShort();
        if (length < 0) throw new DataReadException("Encoded string buffer is smaller than allowed (" + length + " < 0)");

        char[] chars = new char[length];
        for (int i = 0; i < length; i++) chars[i] = this.readChar();
        return new String(chars);
    }

    /**
     * Read a classic string from the stream.

     * This is the string format used by the classic protocol.
     *
     * @return The read string
     * @throws IOException If an I/O error occurs
     */
    public String readClassicString() throws IOException {
        byte[] stringBytes = new byte[64];
        char[] chars = new char[stringBytes.length];
        this.readFully(stringBytes);
        for (int i = 0; i < stringBytes.length; i++) chars[i] = ClassicPing.CP437[stringBytes[i] & 0xFF];
        return new String(chars).trim();
    }

}