The org.jboss.resteasy.plugins.providers.DataSourceProvider class does not properly read from the request input stream. This may result in reading only a part of the input stream.
The method readDataSource() reads from the input stream without actually verifying that the end of the input stream has been reached. Javadoc of InputStream.read() says: "...Reads up to len bytes of data from the input stream into an array of bytes. An attempt is made to read as many as len bytes, but a smaller number may be read. ...".