# Ryu application API

## Ryu application programming model

### Threads, events, and event queues

Ryu applications are single-threaded entities which implement various functionalities in Ryu. Events are messages between them.

Ryu applications send asynchronous events each other. Besides that, there are some Ryu-internal event sources which are not Ryu applications. One of examples of such event sources is OpenFlow controller. While an event can currently contain arbitrary python objects, it’s discouraged to pass complex objects (eg. unpickleable objects) between Ryu applications.

Each Ryu application has a receive queue for events. The queue is FIFO and preserves the order of events. Each Ryu application has a thread for event processing. The thread keep draining the receive queue by dequeueing an event and calling the appropritate event handler for the event type. Because the event handler is called in the context of the event processing thread, it should be careful for blocking. I.e. while an event handler is blocked, no further events for the Ryu application will be processed.

There are kinds of events which are used to implement synchronous inter-application calls between Ryu applications. While such requests uses the same machinary as ordinary events, their replies are put on a queue dedicated to the transaction to avoid deadlock.

While threads and queues is currently implemented with eventlet/greenlet, a direct use of them in a Ryu application is strongly discouraged.

### Contexts

Contexts are ordinary python objects shared among Ryu applications. The use of contexts are discouraged for new code.

## Create a Ryu application

A Ryu application is a python module which defines a subclass of ryu.base.app_manager.RyuApp. If two or more such classes are defined in a module, the first one (by name order) will be picked by app_manager. Ryu application is singleton: only single instance of a given Ryu application is supported.

## Observe events

A Ryu application can register itself to listen for specific events using ryu.controller.handler.set_ev_cls decorator.

## Generate events

A Ryu application can raise events by calling appropriate ryu.base.app_manager.RyuApp’s methods like send_event or send_event_to_observers.

## Event classes

An event class describes a Ryu event generated in the system. By convention, event class names are prefixed by “Event”. Events are generated either by the core part of Ryu or Ryu applications. A Ryu application can register its interest for a specific type of event by providing a handler method using ryu.controller.handler.set_ev_cls decorator.

### OpenFlow event classes

ryu.controller.ofp_event module exports event classes which describe receptions of OpenFlow messages from connected switches. By convention, they are named as ryu.controller.ofp_event.EventOFPxxxx where xxxx is the name of the corresponding OpenFlow message. For example, EventOFPPacketIn for packet-in message. The OpenFlow controller part of Ryu automatically decodes OpenFlow messages received from switches and send these events to Ryu applications which expressed an interest using ryu.controller.handler.set_ev_cls. OpenFlow event classes have at least the following attributes.

Attribute | Description
--- | ---
msg | An object which describes the corresponding OpenFlow message.
msg.datapath | A ryu.controller.controller.Datapath instance which describes an OpenFlow switch from which we received this OpenFlow message.

The msg object has some more additional members whose values are extracted from the original OpenFlow message. See OpenFlow protocol API Reference for more info about OpenFlow messages.

## ryu.base.app_manager.RyuApp

See Ryu API Reference.

## ryu.controller.handler.set_ev_cls(ev_cls, dispatchers=None)

A decorator for Ryu application to declare an event handler. Decorated method will become an event handler. ev_cls is an event class whose instances this RyuApp wants to receive. dispatchers argument specifies one of the following negotiation phases (or a list of them) for which events should be generated for this handler. Note that, in case an event changes the phase, the phase before the change is used to check the interest.

Negotiation phase | Description
--- | ---
ryu.controller.handler.HANDSHAKE_DISPATCHER | Sending and waiting for hello message
ryu.controller.handler.CONFIG_DISPATCHER | Version negotiated and sent features-request message
ryu.controller.handler.MAIN_DISPATCHER | Switch-features message received and sent set-config message
ryu.controller.handler.DEAD_DISPATCHER | Disconnect from the peer. Or disconnecting due to some unrecoverable errors.

## ryu.controller.controller.Datapath

A class to describe an OpenFlow switch connected to this controller. An instance has the following attributes.

Attribute | Description
--- | ---
id | 64-bit OpenFlow Datapath ID. Only available for ryu.controller.handler.MAIN_DISPATCHER phase.
ofproto | A module which exports OpenFlow definitions, mainly constants appeared in the specification, for the negotiated OpenFlow version. For example, ryu.ofproto.ofproto_v1_0 for OpenFlow 1.0.
ofproto_parser | A module which exports OpenFlow wire message encoder and decoder for the negotiated OpenFlow version. For example, ryu.ofproto.ofproto_v1_0_parser for OpenFlow 1.0.
ofproto_parser.OFPxxxx(datapath, ....) | A callable to prepare an OpenFlow message for the given switch. It can be sent with Datapath.send_msg later. xxxx is a name of the message. For example OFPFlowMod for flow-mod message. Arguemnts depend on the message.
set_xid(self, msg) | Generate an OpenFlow XID and put it in msg.xid.
send_msg(self, msg) | Queue an OpenFlow message to send to the corresponding switch. If msg.xid is None, set_xid is automatically called on the message before queueing.
send_packet_out | deprecated
send_flow_mod | deprecated
send_flow_del | deprecated
send_delete_all_flows | deprecated
send_barrier | Queue an OpenFlow barrier message to send to the switch.
send_nxt_set_flow_format | deprecated
is_reserved_port | deprecated

## ryu.controller.event.EventBase

The base of all event classes. A Ryu application can define its own event type by creating a subclass.

## ryu.controller.event.EventRequestBase

The base class for synchronous request for RyuApp.send_request.

## ryu.controller.event.EventReplyBase

The base class for synchronous request reply for RyuApp.send_reply.

## ryu.controller.ofp_event.EventOFPStateChange

An event class for negotiation phase change notification. An instance of this class is sent to observer after changing the negotiation phase. An instance has at least the following attributes.

Attribute | Description
--- | ---
datapath | ryu.controller.controller.Datapath instance of the switch

## ryu.controller.dpset.EventDP

An event class to notify connect/disconnect of a switch. For OpenFlow switches, one can get the same notification by observing ryu.controller.ofp_event.EventOFPStateChange. An instance has at least the following attributes.

Attribute | Description
--- | ---
dp | A ryu.controller.controller.Datapath instance of the switch
enter | True when the switch connected to our controller. False for disconnect.

## ryu.controller.dpset.EventPortAdd

An event class for switch port status notification. This event is generated when a new port is added to a switch. For OpenFlow switches, one can get the same notification by observing ryu.controller.ofp_event.EventOFPPortStatus. An instance has at least the following attributes.

Attribute | Description
--- | ---
dp | A ryu.controller.controller.Datapath instance of the switch
port | port number

## ryu.controller.dpset.EventPortDelete

An event class for switch port status notification. This event is generated when a port is removed from a switch. For OpenFlow switches, one can get the same notification by observing ryu.controller.ofp_event.EventOFPPortStatus. An instance has at least the following attributes.

Attribute | Description
--- | ---
dp | A ryu.controller.controller.Datapath instance of the switch
port | port number

## ryu.controller.dpset.EventPortModify

An event class for switch port status notification. This event is generated when some attribute of a port is changed. For OpenFlow switches, one can get the same notification by observing ryu.controller.ofp_event.EventOFPPortStatus. An instance has at least the following attributes.

Attribute | Description
--- | ---
dp | A ryu.controller.controller.Datapath instance of the switch
port | port number

## ryu.controller.network.EventNetworkPort

An event class for notification of port arrival and deperture. This event is generated when a port is introduced to or removed from a network by the REST API. An instance has at least the following attributes.

Attribute | Description
--- | ---
network_id | Network ID
dpid | OpenFlow Datapath ID of the switch to which the port belongs.
port_no | OpenFlow port number of the port
add_del | True for adding a port. False for removing a port.

## ryu.controller.network.EventNetworkDel

An event class for network deletion. This event is generated when a network is deleted by the REST API. An instance has at least the following attributes.

Attribute | Description
--- | ---
network_id | Network ID

## ryu.controller.network.EventMacAddress

An event class for end-point MAC address registration. This event is generated when a end-point MAC address is updated by the REST API. An instance has at least the following attributes.

Attribute | Description
--- | ---
network_id | Network ID
dpid | OpenFlow Datapath ID of the switch to which the port belongs.
port_no | OpenFlow port number of the port
mac_address | The old MAC address of the port if add_del is False. Otherwise the new MAC address.
add_del | False if this event is a result of a port removal. Otherwise True.

## ryu.controller.tunnels.EventTunnelKeyAdd

An event class for tunnel key registration. This event is generated when a tunnel key is registered or updated by the REST API. An instance has at least the following attributes.

Attribute | Description
--- | ---
network_id | Network ID
tunnel_key | Tunnel Key

## ryu.controller.tunnels.EventTunnelKeyDel

An event class for tunnel key registration. This event is generated when a tunnel key is removed by the REST API. An instance has at least the following attributes.

Attribute | Description
--- | ---
network_id | Network ID
tunnel_key | Tunnel Key

## ryu.controller.tunnels.EventTunnelPort

An event class for tunnel port registration. This event is generated when a tunnel port is added or removed by the REST API. An instance has at least the following attributes.

Attribute | Description
--- | ---
dpid | OpenFlow Datapath ID
port_no | OpenFlow port number
remote_dpid | OpenFlow port number of the tunnel peer
add_del | True for adding a tunnel. False for removal.