[govpp.git] / api / api.go

// Copyright (c) 2017 Cisco and/or its affiliates.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at:
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package api

import (
        "errors"
        "fmt"
        "time"
)

// MessageType represents the type of a VPP message.
type MessageType int

const (
        // RequestMessage represents a VPP request message
        RequestMessage MessageType = iota
        // ReplyMessage represents a VPP reply message
        ReplyMessage
        // OtherMessage represents other VPP message (e.g. counters)
        OtherMessage
)

// Message is an interface that is implemented by all VPP Binary API messages generated by the binapi_generator.
type Message interface {
        // GetMessageName returns the original VPP name of the message, as defined in the VPP API.
        GetMessageName() string

        // GetMessageType returns the type of the VPP message.
        GetMessageType() MessageType

        // GetCrcString returns the string with CRC checksum of the message definition (the string represents a hexadecimal number).
        GetCrcString() string
}

// DataType is an interface that is implemented by all VPP Binary API data types by the binapi_generator.
type DataType interface {
        // GetTypeName returns the original VPP name of the data type, as defined in the VPP API.
        GetTypeName() string

        // GetCrcString returns the string with CRC checksum of the data type definition (the string represents a hexadecimal number).
        GetCrcString() string
}

// ChannelProvider provides the communication channel with govpp core.
type ChannelProvider interface {
        // NewAPIChannel returns a new channel for communication with VPP via govpp core.
        // It uses default buffer sizes for the request and reply Go channels.
        NewAPIChannel() (*Channel, error)

        // NewAPIChannel returns a new channel for communication with VPP via govpp core.
        // It allows to specify custom buffer sizes for the request and reply Go channels.
        NewAPIChannelBuffered() (*Channel, error)
}

// MessageDecoder provides functionality for decoding binary data to generated API messages.
type MessageDecoder interface {
        // DecodeMsg decodes binary-encoded data of a message into provided Message structure.
        DecodeMsg(data []byte, msg Message) error
}

// MessageIdentifier provides identification of generated API messages.
type MessageIdentifier interface {
        // GetMessageID returns message identifier of given API message.
        GetMessageID(msg Message) (uint16, error)
}

// Channel is the main communication interface with govpp core. It contains two Go channels, one for sending the requests
// to VPP and one for receiving the replies from it. The user can access the Go channels directly, or use the helper
// methods  provided inside of this package. Do not use the same channel from multiple goroutines concurrently,
// otherwise the responses could mix! Use multiple channels instead.
type Channel struct {
        ReqChan   chan *VppRequest // channel for sending the requests to VPP, closing this channel releases all resources in the ChannelProvider
        ReplyChan chan *VppReply   // channel where VPP replies are delivered to

        NotifSubsChan      chan *NotifSubscribeRequest // channel for sending notification subscribe requests
        NotifSubsReplyChan chan error                  // channel where replies to notification subscribe requests are delivered to

        MsgDecoder    MessageDecoder    // used to decode binary data to generated API messages
        MsgIdentifier MessageIdentifier // used to retrieve message ID of a message

        replyTimeout time.Duration // maximum time that the API waits for a reply from VPP before returning an error, can be set with SetReplyTimeout
        metadata     interface{}   // opaque metadata of the API channel
}

// VppRequest is a request that will be sent to VPP.
type VppRequest struct {
        Message   Message // binary API message to be send to VPP
        Multipart bool    // true if multipart response is expected, false otherwise
}

// VppReply is a reply received from VPP.
type VppReply struct {
        MessageID         uint16 // ID of the message
        Data              []byte // encoded data with the message - MessageDecoder can be used for decoding
        LastReplyReceived bool   // in case of multipart replies, true if the last reply has been already received and this one should be ignored
        Error             error  // in case of error, data is nil and this member contains error description
}

// NotifSubscribeRequest is a request to subscribe for delivery of specific notification messages.
type NotifSubscribeRequest struct {
        Subscription *NotifSubscription // subscription details
        Subscribe    bool               // true if this is a request to subscribe, false if unsubscribe
}

// NotifSubscription represents a subscription for delivery of specific notification messages.
type NotifSubscription struct {
        NotifChan  chan Message   // channel where notification messages will be delivered to
        MsgFactory func() Message // function that returns a new instance of the specific message that is expected as a notification
}

// RequestCtx is a context of a ongoing request (simple one - only one response is expected).
type RequestCtx struct {
        ch *Channel
}

// MultiRequestCtx is a context of a ongoing multipart request (multiple responses are expected).
type MultiRequestCtx struct {
        ch *Channel
}

const defaultReplyTimeout = time.Second * 1 // default timeout for replies from VPP, can be changed with SetReplyTimeout

// NewChannelInternal returns a new channel structure with metadata field filled in with the provided argument.
// Note that this is just a raw channel not yet connected to VPP, it is not intended to be used directly.
// Use ChannelProvider to get an API channel ready for communication with VPP.
func NewChannelInternal(metadata interface{}) *Channel {
        return &Channel{
                replyTimeout: defaultReplyTimeout,
                metadata:     metadata,
        }
}

// Metadata returns the metadata stored within the channel structure by the NewChannelInternal call.
func (ch *Channel) Metadata() interface{} {
        return ch.metadata
}

// SetReplyTimeout sets the timeout for replies from VPP. It represents the maximum time the API waits for a reply
// from VPP before returning an error.
func (ch *Channel) SetReplyTimeout(timeout time.Duration) {
        ch.replyTimeout = timeout
}

// Close closes the API channel and releases all API channel-related resources in the ChannelProvider.
func (ch *Channel) Close() {
        if ch.ReqChan != nil {
                close(ch.ReqChan)
        }
}

// SendRequest asynchronously sends a request to VPP. Returns a request context, that can be used to call ReceiveReply.
// In case of any errors by sending, the error will be delivered to ReplyChan (and returned by ReceiveReply).
func (ch *Channel) SendRequest(msg Message) *RequestCtx {
        ch.ReqChan <- &VppRequest{
                Message: msg,
        }
        return &RequestCtx{ch: ch}
}

// ReceiveReply receives a reply from VPP (blocks until a reply is delivered from VPP, or until an error occurs).
// The reply will be decoded into the msg argument. Error will be returned if the response cannot be received or decoded.
func (req *RequestCtx) ReceiveReply(msg Message) error {
        if req == nil || req.ch == nil {
                return errors.New("invalid request context")
        }

        lastReplyReceived, err := req.ch.receiveReplyInternal(msg)

        if lastReplyReceived {
                err = errors.New("multipart reply recieved while a simple reply expected")
        }
        return err
}

// SendMultiRequest asynchronously sends a multipart request (request to which multiple responses are expected) to VPP.
// Returns a multipart request context, that can be used to call ReceiveReply.
// In case of any errors by sending, the error will be delivered to ReplyChan (and returned by ReceiveReply).
func (ch *Channel) SendMultiRequest(msg Message) *MultiRequestCtx {
        ch.ReqChan <- &VppRequest{
                Message:   msg,
                Multipart: true,
        }
        return &MultiRequestCtx{ch: ch}
}

// ReceiveReply receives a reply from VPP (blocks until a reply is delivered from VPP, or until an error occurs).
// The reply will be decoded into the msg argument. If the last reply has been already consumed, LastReplyReceived is
// set to true. Do not use the message itself if LastReplyReceived is true - it won't be filled with actual data.
// Error will be returned if the response cannot be received or decoded.
func (req *MultiRequestCtx) ReceiveReply(msg Message) (LastReplyReceived bool, err error) {
        if req == nil || req.ch == nil {
                return false, errors.New("invalid request context")
        }

        return req.ch.receiveReplyInternal(msg)
}

// receiveReplyInternal receives a reply from the reply channel into the provided msg structure.
func (ch *Channel) receiveReplyInternal(msg Message) (LastReplyReceived bool, err error) {
        if msg == nil {
                return false, errors.New("nil message passed in")
        }
        select {
        // blocks until a reply comes to ReplyChan or until timeout expires
        case vppReply := <-ch.ReplyChan:
                if vppReply.Error != nil {
                        err = vppReply.Error
                        return
                }
                if vppReply.LastReplyReceived {
                        LastReplyReceived = true
                        return
                }
                // message checks
                expMsgID, err := ch.MsgIdentifier.GetMessageID(msg)
                if err != nil {
                        err = fmt.Errorf("message %s with CRC %s is not compatible with the VPP we are connected to",
                                msg.GetMessageName(), msg.GetCrcString())
                        return false, err
                }
                if vppReply.MessageID != expMsgID {
                        err = fmt.Errorf("invalid message ID %d, expected %d "+
                                "(also check if multiple goroutines are not sharing one GoVPP channel)", vppReply.MessageID, expMsgID)
                        return false, err
                }
                // decode the message
                err = ch.MsgDecoder.DecodeMsg(vppReply.Data, msg)

        case <-time.After(ch.replyTimeout):
                err = fmt.Errorf("no reply received within the timeout period %ds", ch.replyTimeout/time.Second)
        }
        return
}

// SubscribeNotification subscribes for receiving of the specified notification messages via provided Go channel.
// Note that the caller is responsible for creating the Go channel with preferred buffer size. If the channel's
// buffer is full, the notifications will not be delivered into it.
func (ch *Channel) SubscribeNotification(notifChan chan Message, msgFactory func() Message) (*NotifSubscription, error) {
        subscription := &NotifSubscription{
                NotifChan:  notifChan,
                MsgFactory: msgFactory,
        }
        ch.NotifSubsChan <- &NotifSubscribeRequest{
                Subscription: subscription,
                Subscribe:    true,
        }
        return subscription, <-ch.NotifSubsReplyChan
}

// UnsubscribeNotification unsubscribes from receiving the notifications tied to the provided notification subscription.
func (ch *Channel) UnsubscribeNotification(subscription *NotifSubscription) error {
        ch.NotifSubsChan <- &NotifSubscribeRequest{
                Subscription: subscription,
                Subscribe:    false,
        }
        return <-ch.NotifSubsReplyChan
}

// CheckMessageCompatibility checks whether provided messages are compatible with the version of VPP
// which the library is connected to.
func (ch *Channel) CheckMessageCompatibility(messages ...Message) error {
        for _, msg := range messages {
                _, err := ch.MsgIdentifier.GetMessageID(msg)
                if err != nil {
                        return fmt.Errorf("message %s with CRC %s is not compatible with the VPP we are connected to",
                                msg.GetMessageName(), msg.GetCrcString())
                }
        }
        return nil
}