Related to spring-projects/spring-framework#25744
Simply run mvn clean package to build the project, and java -jar target/spring-content-length-sample-0.0.1-SNAPSHOT.jar to run the Spring application.
A Ruby script is available to simulate the case where a Content-Length is specified in the request, but the connection is terminated before the required number of bytes is sent. Simply run bundle install and bundle exec ruby request.rb to execute it.