BencodeDecoder

package me.rabrg.bencode;

import java.io.IOException;
import java.io.InputStream;
import java.nio.charset.Charset;

public final class BencodeDecoder {

    private static final Charset CHARSET = Charset.forName("US-ASCII");

    private final byte[] buffer;

    private int pos = 0;

    public BencodeDecoder(final InputStream inputStream) throws IOException {
        buffer = new byte[inputStream.available()];
        inputStream.read(buffer);
    }

    public BencodeDecoder(final String string) {
        buffer = string.getBytes(CHARSET);
    }

    public BencodeDecoder(final byte[] bytes) {
        buffer = bytes;
    }

    public Object read() {
        if (buffer[pos] >= '0' && buffer[pos] <= '9') {
            return readString();
        } else if (buffer[pos] == 'i') {
            return readInteger();
        }
        throw new IllegalStateException("the byte " + buffer[pos] + " (char " + (char) buffer[pos] + ") is not a valid key");
    }

    private int readInteger() {
        final int start = ++pos;
        while (buffer[pos] != 'e') {
            pos++;
        }
        return Integer.parseInt(new String(buffer, start, pos++ - start, CHARSET));
    }

    private String readString() {
        final int start = pos++;
        while (buffer[pos++] != ':') {
        }
        final String string = new String(buffer, pos, Integer.parseInt(new String(buffer, start, pos - start - 1, CHARSET)), CHARSET);
        pos += string.length();
        return string;
    }
}