There is a whole class of attacks called HTTP Desync Attacks that target just that problem since it is hard to get that right, especially accross multiple diffe

There is a whole class of attacks called HTTP Desync Attacks that target just that problem since it is hard to get that right, especially accross multiple different http stacks. And if you dont get it right the result.is that bytes are left on the TCP connections and read as the next request in case of a reuse.