private void decrementOutstandingUserCalls() {
        var remaining = numberOfOutstandingUserCalls.decrementAndGet();
        if (remaining == 0) {
            jettyReadCompletion.complete(null);
        }
        if (remaining < 0) {
            throw new AssertionError("Number of outstanding user calls is negative: " + remaining);
        }
    }
Reads request content from a Jetty {@link Request} and writes it to the {@link ContentChannel}
returned by the {@link com.yahoo.jdisc.handler.RequestHandler}.

@author bjorncs
container-core/src/main/java/com/yahoo/jdisc/http/server/jetty/JettyRequestContentReader.java