To cope with the growing performance needs of appliances in datacenters or the network edge, current middlebox functionalities such as firewalls, NAT, DPI, content-aware optimizers or load-balancers are often implemented on multiple (perhaps virtual) machines.In this work, we design a system able to run a pipeline of VNFs with a high level of parallelism to handle many flows. We provide the user facilities to define the traffic class of interest for the VNF, a definition of session to group the packets such as the TCP 4-tuples, and the amount of space per sessions. The system will then synthesize the classification and build a unique, efficient flow table. We build an abstract view of flows and use it to implement support for seamless inspection and modification of the content of any flow (such as TCP or HTTP), automatically reflecting a consistent view, across layers, of flows modified onthe-fly.Our prototype gives rise to a user-space software NFV dataplane enabling easy implementation of middlebox functionalities, as well as the deployment of complex scenarios. Our prototype implementation is able to handle our testbed limit of ~34 Gbps of HTTP requests (for 8-KB files) through a service chain of multiples stateful VNFs, on a single Xeon core.