websocket-driver-ruby/ext/websocket_driver/com/jcoglan/websocket/Unparser.java

package com.jcoglan.websocket;

public class Unparser {
    private static final byte
        FIN                   = -0x80,
        RSV1                  =  0x40,
        RSV2                  =  0x20,
        RSV3                  =  0x10,
        OPCODE                =  0x0f,
        MASK                  = -0x80,
        LENGTH                =  0x7f;

    private boolean masking;

    public Unparser(boolean masking) {
        this.masking = masking;
    }

    public byte[] frame(Frame frame) {
        int flen    = (int)frame.length,
            lenlen  = (flen <= 125) ? 0 : (flen <= 65535) ? 2 : 8,
            masklen = masking ? 4 : 0,
            buflen  = 2 + lenlen + masklen + flen;

        byte[] buf  = new byte[buflen];
        int mask    = 0;

        buf[0] = (byte)( (frame.fin  ? FIN  : 0)
                       | (frame.rsv1 ? RSV1 : 0)
                       | (frame.rsv2 ? RSV2 : 0)
                       | (frame.rsv3 ? RSV3 : 0)
                       | frame.opcode );

        if (masking) {
            frame.masked = true;
            Frame.mask(frame);
            mask = MASK;
        }

        long length = frame.length;

        if (lenlen == 0) {
            buf[1] = (byte)(mask | length);

        } else if (lenlen == 2) {
            buf[1] = (byte)(mask | 126);
            Buffer.writeUInt16(buf, 2, length);
        } else {
            buf[1] = (byte)(mask | 127);
            Buffer.writeUInt64(buf, 2, length);
        }

        System.arraycopy(frame.maskingKey, 0, buf, 2 + lenlen, masklen);
        System.arraycopy(frame.payload, 0, buf, 2 + lenlen + masklen, flen);

        return buf;
    }
}