refactor: now Hub keeps everything

before this there was some hidden race condition because raceCondition
is not concurrent-safe, and there was some concurrent reading and
writing.
Now everything is handled safely by the Hub.

Client now have "options" which are understood by the Hub to handle
them differently.

http.go

@@ -1,7 +1,6 @@
 package main
 
 import (
-	"container/ring"
 	"net/http"
 	"time"
 
@@ -9,25 +8,27 @@ import (
 	"gopkg.in/mcuadros/go-syslog.v2/format"
 )
 
-func setupHttp(circbuf *ring.Ring, hub Hub) {
-	http.HandleFunc("/", getHTTPHandler(circbuf))
+func setupHttp(hub Hub) {
+	http.HandleFunc("/", getHTTPHandler(hub))
 	http.HandleFunc("/ws", getWSHandler(hub))
 }
 
-func getHTTPHandler(circbuf *ring.Ring) http.HandlerFunc {
+func getHTTPHandler(hub Hub) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
-		circbuf.Do(func(x interface{}) {
-			if x == nil {
-				return
-			}
-			logmsg := x.(format.LogParts)
+		client := Client{
+			Messages: make(chan format.LogParts),
+			Nofollow: true}
+		hub.Register <- client
+
+		for x := range client.Messages {
+			logmsg := x
 			if logmsg["message"] == nil {
-				return
+				continue
 			}
 			c := logmsg["message"].(string)
 			w.Write([]byte(c))
 			w.Write([]byte("\n"))
-		})
+		}
 	}
 }
 
@@ -41,7 +42,7 @@ func getWSHandler(hub Hub) http.HandlerFunc {
 		if err != nil {
 			return
 		}
-		client := Client{messages: make(chan format.LogParts)}
+		client := Client{Messages: make(chan format.LogParts)}
 		hub.Register <- client
 
 		// Allow collection of memory referenced by the caller by doing all work in
@@ -53,7 +54,7 @@ func getWSHandler(hub Hub) http.HandlerFunc {
 			}()
 			for {
 				select {
-				case message, ok := <-c.messages:
+				case message, ok := <-c.Messages:
 					conn.SetWriteDeadline(time.Now().Add(10 * time.Second))
 					if !ok {
 						// The hub closed the channel.

hub.go

@@ -1,49 +1,71 @@
 package main
 
 import (
-	"fmt"
+	"container/ring"
 
 	"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. It is a struct so that it can later be "expanded" to contain other fields (ie:
-// filters)
+// new messages are sent.
 type Client struct {
-	messages chan format.LogParts
+	Messages chan format.LogParts // only hub should write/close this
+	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"
+// 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
 type Hub struct {
-	clients     map[Client]bool
 	Register    chan Client
 	Unregister  chan Client
-	logMessages chan format.LogParts
+	LogMessages chan format.LogParts
+
+	clients map[Client]bool
+	circbuf *ring.Ring
 }
 
 // NewHub creates an empty hub
-func NewHub() 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),
+		LogMessages: make(chan format.LogParts),
+		circbuf:     ring.New(ringBufSize),
 	}
 }
 
+// Run is hub main loop; keeps everything going
 func (h *Hub) Run() {
 	for {
 		select {
 		case cl := <-h.Register:
+			if _, ok := h.clients[cl]; !ok {
+				if !cl.Nofollow { // we won't need it in future
 					h.clients[cl] = true
+				}
+				h.circbuf.Do(func(x interface{}) {
+					if x != nil {
+						cl.Messages <- x.(format.LogParts)
+					}
+				})
+				if cl.Nofollow {
+					close(cl.Messages)
+				}
+			}
 		case cl := <-h.Unregister:
 			_, ok := h.clients[cl]
 			if ok {
+				close(cl.Messages)
 				delete(h.clients, cl)
 			}
-		case msg := <-h.logMessages:
-			fmt.Println("ricevuto", msg["message"], len(h.clients))
+		case msg := <-h.LogMessages:
+			h.circbuf.Value = msg
+			h.circbuf = h.circbuf.Next()
 			for client := range h.clients {
-				client.messages <- msg
+				client.Messages <- msg
 			}
 		}
 	}

main.go

@@ -1,27 +1,14 @@
 package main
 
 import (
-	"container/ring"
 	"flag"
 	"fmt"
 	"net/http"
 	"os"
 
 	syslog "gopkg.in/mcuadros/go-syslog.v2"
-	"gopkg.in/mcuadros/go-syslog.v2/format"
 )
 
-func getSyslogdHandler(circbuf *ring.Ring, hub Hub) func(channel syslog.LogPartsChannel) {
-	return func(channel syslog.LogPartsChannel) {
-		for logParts := range channel {
-			hub.logMessages <- logParts
-			fmt.Println(logParts)
-			circbuf.Value = logParts
-			circbuf = circbuf.Next()
-		}
-	}
-}
-
 func main() {
 	var err error
 	syslogSocketPath := flag.String("syslogd-socket", "", "The socket to listen to syslog addresses")
@@ -32,9 +19,8 @@ func main() {
 	flag.Parse()
 
 	var hub Hub
-	hub = NewHub()
-	channel := make(chan format.LogParts)
-	handler := syslog.NewChannelHandler(channel)
+	hub = NewHub(*bufsize)
+	handler := syslog.NewChannelHandler(hub.LogMessages)
 
 	server := syslog.NewServer()
 	server.SetFormat(syslog.RFC5424)
@@ -52,15 +38,13 @@ func main() {
 			os.Exit(1)
 		}
 	}
-	circbuf := ring.New(*bufsize)
 	if err = server.Boot(); err != nil {
 		fmt.Fprintln(os.Stderr, "argh", err)
 		os.Exit(1)
 	}
 	go hub.Run()
-	go getSyslogdHandler(circbuf, hub)(channel)
 
-	setupHttp(circbuf, hub)
+	setupHttp(hub)
 	fmt.Printf("Binding address `%s` [http]\n", *queryAddr)
 	http.ListenAndServe(*queryAddr, nil)
 	server.Wait()