For when a single passthrough stream is not enough.
var dp = new DuplexPassThrough(stream, options);
Or, if the stream is not available yet:
var dp = new DuplexPassThrough(null, options); // some time later.. dp.wrapStream(stream);
This is useful if you have to buffer up both sides of a duplex stream for some reason, like if you want to read some bits of a socket, but then send it somewhere else, or do other crazy stuff.