public SocketIO addHeader(String key, String value) {
		if (this.connection != null)
			throw new RuntimeException(
					"You may only set headers before connecting.\n"
							+ " Try to use new SocketIO().addHeader(key, value).connect(host, callback) "
							+ "instead of SocketIO(host, callback).addHeader(key, value)");
		this.headers.setProperty(key, value);
		return this;
	}
Adds an header to the {@link #headers}
@return SocketIO.this for daisy chaining.
src/io/socket/SocketIO.java