circolog/hub.go

package circolog

import (
	"container/ring"
	"time"

	"gopkg.in/mcuadros/go-syslog.v2/format"
)

// Client represent a client connected via websocket. Its most important field is the messages channel, where
// new messages are sent.
type Client struct {
	Messages chan format.LogParts // only hub should write/close this
	Options  ClientOptions
}

type ClientOptions struct {
	BacklogLength int  // how many past messages the client wants to receive upon connection
	Nofollow      bool // if Nofollow is true, the hub will not keep this client permanently. Rather, it will send every message to "Messages" and close the channel. Use this if you want to get the messages one-shot
}

// The Hub is the central "registry"; it keeps both the data storage and clients notifications
//
// The channel "register" and "unregister" can be seen as "command"
// keep in mind that "registering" is what you do also to get messages in a one-time fashion. In fact, Client
// has "options", such as Nofollow, to explain the Hub what should be given

// An HubCommand is an "enum" of different commands
type HubCommand int

const (
	CommandClear       = iota
	CommandPauseToggle = iota
)

// An HubFullCommand is a Command, complete with arguments
type HubFullCommand struct {
	Command  HubCommand
	Response chan CommandResponse
}
type CommandResponse struct {
	Value interface{}
}

type Hub struct {
	Register    chan Client
	Unregister  chan Client
	LogMessages chan format.LogParts
	Commands    chan HubFullCommand

	clients map[Client]bool
	circbuf *ring.Ring
}

// NewHub creates an empty hub
func NewHub(ringBufSize int) Hub {
	return Hub{clients: make(map[Client]bool),
		Register:    make(chan Client),
		Unregister:  make(chan Client),
		LogMessages: make(chan format.LogParts),
		Commands:    make(chan HubFullCommand),
		circbuf:     ring.New(ringBufSize),
	}
}

func (h *Hub) register(cl Client) {
	if _, ok := h.clients[cl]; !ok {
		if !cl.Options.Nofollow { // we won't need it in future
			h.clients[cl] = true
		}

		howmany := cl.Options.BacklogLength
		if howmany > h.circbuf.Len() || howmany == -1 {
			howmany = h.circbuf.Len()
		}
		buf := h.circbuf.Move(-howmany)
		for i := 0; i < howmany; i++ {
			item := buf.Value
			if item != nil {
				select { // send with short timeout
				case cl.Messages <- item.(format.LogParts):
					break
				case <-time.After(500 * time.Millisecond):
					close(cl.Messages)
					return
				}
			}

			buf = buf.Next()
		}

		if cl.Options.Nofollow {
			close(cl.Messages)
		}
	}
}

// Run is hub main loop; keeps everything going
func (h *Hub) Run() {
	active := true
	for {
		select {
		case cl := <-h.Register:
			h.register(cl)
		case cl := <-h.Unregister:
			_, ok := h.clients[cl]
			if ok {
				close(cl.Messages)
				delete(h.clients, cl)
			}
		case msg := <-h.LogMessages:
			if active == true {
				h.circbuf.Value = msg
				h.circbuf = h.circbuf.Next()
				for client := range h.clients {
					select { // send without blocking
					case client.Messages <- msg:
						break
					default:
						break
					}
				}
			}
		case cmd := <-h.Commands:
			if cmd.Command == CommandClear {
				h.clear()
				cmd.Response <- CommandResponse{Value: true}
			}
			if cmd.Command == CommandPauseToggle {
				active = !active
				cmd.Response <- CommandResponse{Value: active}
			}
		}
	}
}

// Clear removes all elements from the buffer
func (h *Hub) clear() {
	buf := h.circbuf
	for i := 0; i < buf.Len(); i++ {
		buf.Value = nil
		buf = buf.Next()
	}
}