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+.. _quic_plugin:
+.. _quicly: https://github.com/h2o/quicly
+
+.. toctree::
+
+QUIC HostStack
+==============
+
+The quic plugin provides an `IETF QUIC protocol <https://tools.ietf.org/html/draft-ietf-quic-transport-22>`_ implementation. It is based on
+the quicly_ library.
+
+This plugin adds the QUIC protocol to VPP's Host Stack. As a result QUIC is
+usable both in internal VPP applications and in external apps.
+
+**Maturity**
+
+- This plugin is under current development: it should mostly work, but has not been thoroughly tested and should not be used in production.
+- Only bidirectional streams are supported currently.
+
+Getting started
+---------------
+
+* A common sample setup is with two vpp instances interconnected #twovppinstances
+* Ensure your vpp configuration file contains ``session { evt_qs_memfd_seg }``
+* Then run ``session enable`` in the debug cli (vppctl)
+
+This plugin can be tested in the following cases.
+
+Internal client
+^^^^^^^^^^^^^^^
+
+This application is a simple command to be run on the debug cli to test connectivity & throughput on QUIC over the debug cli (vppctl). It does not reflect reality and is mostly used for internal tests.
+
+* Run ``test echo server uri quic://1.1.1.1/1234`` on your first instance
+* Then ``test echo client uri quic://20.20.1.1/1`` on the second one
+
+Source for the internal client lives in ``src/plugins/hs_apps/echo_client.c``
+
+External client
+^^^^^^^^^^^^^^^
+
+This setup reflects the use case of an app developper using vpp to create a quic client / server. The application is an external binary that connects to VPP via its binary API.
+
+After having setup two interconnected vpps, you can attach the quic_echo binary to each of them.
+
+* The binary can be found in ``./build-root/build-vpp[_debug]-native/vpp/bin/quic_echo``
+* To run the client & server use ``quic_echo socket-name /vpp.sock client|server uri quic://1.1.1.1/1234``
+* Several options are available to customize the amount of data sent, number of threads, logging and timinig.
+
+The behavior of this app when run with ``nclient 2/4`` is two first establish 2 connections with the given peer, and once everything has been openend start opening 4 quic streams, and transmit data. Flow is as follows.
+
+.. image:: /_images/quic_plugin_echo_flow.png
+
+This allows timinig of either the whole setup & teardown or specific phases in assessing the protocol's performance
+
+Source for the internal client lives in ``src/plugins/hs_apps/sapi/quic_echo.c``
+
+VCL client
+^^^^^^^^^^
+
+The hoststack exposes a simplified API call the VCL (blocking posix like calls), this API is used by a sample client & server implementation that supports QUIC, TCP and UDP.
+
+* The binaries can be found in ``./build-root/build-vpp[_debug]-native/vpp/bin/``
+* Create the VCL conf files ``echo "vcl { api-socket-name /vpp.sock }" | tee /tmp/vcl.conf]``
+* For the server ``VCL_CONFIG=/tmp/vcl.conf ; vcl_test_server -p QUIC 1234"``
+* For the client ``VCL_CONFIG=/tmp/vcl.conf ; vcl_test_client -p QUIC 1.1.1.1 1234"``
+
+Source for the internal client lives in ``src/plugins/hs_apps/vcl/vcl_test_client.c``
+
+A basic usage is the following client side
+
+.. code-block:: C
+
+  #include <vcl/vppcom.h>
+  int fd = vppcom_session_create (VPPCOM_PROTO_QUIC);
+  vppcom_session_tls_add_cert (/* args */);
+  vppcom_session_tls_add_key (/* args */);
+  vppcom_session_connect (fd, "quic://1.1.1.1/1234"); /* create a quic connection */
+  int sfd = vppcom_session_create (VPPCOM_PROTO_QUIC);
+  vppcom_session_stream_connect (sfd, fd); /* open a quic stream on the connection*/
+  vppcom_session_write (sfd, buf, n);
+
+Server side
+
+.. code-block:: C
+
+  #include <vcl/vppcom.h>
+  int lfd = vppcom_session_create (VPPCOM_PROTO_QUIC);
+  vppcom_session_tls_add_cert (/* args */);
+  vppcom_session_tls_add_key (/* args */);
+  vppcom_session_bind (fd, "quic://1.1.1.1/1234");
+  vppcom_session_listen (fd);
+  int fd = vppcom_session_accept (lfd); /* accept quic connection*/
+  vppcom_session_is_connectable_listener (fd); /* is true */
+  int sfd = vppcom_session_accept (fd); /* accept quic stream */
+  vppcom_session_is_connectable_listener (sfd); /* is false */
+  vppcom_session_read (sfd, buf, n);
+
+
+Internal Mechanics
+------------------
+
+QUIC constructs are exposed as follows:
+
+- QUIC connections and streams are both regular host stack session, exposed via the API with their 64bits handle.
+- QUIC connections can be created and destroyed with regular ``connect`` and ``close`` calls with ``TRANSPORT_PROTO_QUIC``.
+- Streams can be opened in a connection by calling ``connect`` again and passing the handle of the connection to which the new stream should belong.
+- Streams can be closed with a regular ``close`` call.
+- Streams opened by peers can be accepted from the sessions corresponding to QUIC connections.
+- Data can ba exchanged by using the regular ``send`` and ``recv`` calls on the stream sessions.
+
+Data structures
+^^^^^^^^^^^^^^^
+
+Quic relies on the hoststack constructs, namely applications, sessions, transport_connections, and app_listeners. When listening on a port with the quic protocol, an external application :
+
+* Attaches to vpp and register an ``application``
+* It creates an ``app_listener`` and a ``quic_listen_session``.
+* The ``quic_listen_session`` relies on a ``transport_connection`` (``lctx``) to access the underlying ``udp_listen_session`` that will receive packets.
+* Upon connection request, we create the same data structure (``quic_session``, ``qctx``, ``udp_session``) and pass a handle to the ``quic_session`` in the accept callback to acknowledge the creation of a quic connection. All further UDP datagrams for the peers at each end of the connection will be exchanged through the ``udp_session``
+* Upon receiving a Stream opening request, we create the ``stream_session`` and its transport ``sctx`` and pass the handle to the ``stream_session`` back to the app. Here we don't have any UDP datastructures, as all datagrams are bound to the connection.
+
+
+Thoses structures are linked as follows :
+
+.. image:: /_images/quic_plugin_datastructures.png
+