Pumps data from a ReadStream to a WriteStream and performs flow control where necessary to prevent the write stream buffer from getting overfull.

Instances of this class read bytes from a ReadStream and write them to a WriteStream. If data can be read faster than it can be written this could result in the write queue of the WriteStream growing without bound, eventually causing it to exhaust all available RAM.

To prevent this, after each write, instances of this class check whether the write queue of the WriteStream is full, and if so, the {@link ReadStream} is paused, and a WriteStream.drainHandler() is set on the WriteStream. When the WriteStream has processed half of its backlog, the WriteStream.drainHandler() will be called, which results in the pump resuming the ReadStream.

This class can be used to pump from any ReadStream to any WriteStream, e.g. from an HttpServerRequest to an {@link org.vertx.java.core.file.AsyncFile} (todo), or from {@link org.vertx.java.core.net.NetSocket} (todo) to a {@link org.vertx.java.core.http.WebSocket} (todo).

Instances of this class are not thread-safe.