Cache times

README.md

@@ -9,6 +9,7 @@ Flags are supplied to the compiled go program in the form ```-flag=stuff```.
 | Flag | Description | Default |
 | ---- | ----------- | ------- |
 | listen | Port number to listen on | 8080 |
+| redis | Host and port of redis | :6379 |
 
 ## API
 
@@ -18,7 +19,7 @@ Flags are supplied to the compiled go program in the form ```-flag=stuff```.
 GET /subscribe/:userid/client/:clientid
 ```
 
-Subscribe to a user. Every time a user pings this service, the time will be sent to all subscribed users.
+Subscribe to a user. Every time a user pings this service, the time will be sent to all subscribed users. Upon subscription, if it exists, the last cached time of the target user will be pushed immediately to the stream.
 
 ```js
 const es = new EventSource(`${host}/subscribe/${user}/client/${device}`);

main.go

@@ -9,9 +9,11 @@ import (
   "time"
 
   "github.com/julienschmidt/httprouter"
+  "github.com/go-redis/redis"
 )
 
 var listen string
+var redisHost string
 
 type RawClient struct {
   UserId string
@@ -19,14 +21,23 @@ type RawClient struct {
 }
 
 var connections map[RawClient][]chan []byte
+var redisClient *redis.Client
 
 func main() {
   // Parse flags
   flag.StringVar(&listen, "listen", ":8080", "host and port to listen on")
+  flag.StringVar(&redisHost, "redis", ":6379", "host and port of redis")
   flag.Parse()
 
   connections = make(map[RawClient][]chan []byte)
 
+  // Redis
+  redisClient = redis.NewClient(&redis.Options{
+    Addr: redisHost,
+    Password: "",
+    DB: 0,
+  })
+
   // Routes
 	router := httprouter.New()
   router.GET("/subscribe/:userid/client/:clientid", Subscribe)
@@ -59,6 +70,13 @@ func Subscribe(w http.ResponseWriter, r *http.Request, p httprouter.Params) {
   resClosed := w.(http.CloseNotifier).CloseNotify()
   ticker := time.NewTicker(25 * time.Second)
 
+  // Push cached value (if it exists) to the connection
+  cachedTime, err := redisClient.Get(client.UserId + client.ClientId).Result()
+  if err == nil {
+    fmt.Fprintf(w, "data: %s\n\n", cachedTime)
+    flusher.Flush()
+  }
+
   for {
     select {
       case msg := <- recv:
@@ -81,10 +99,12 @@ func PostTime(w http.ResponseWriter, r *http.Request, p httprouter.Params) {
     ClientId: p.ByName("clientid"),
   }
 
-  time := time.Now().UTC().Unix()
+  time := []byte(strconv.FormatInt(time.Now().UTC().Unix(), 10)) // UTC Epoch Time in []byte
+  key := client.UserId + client.ClientId
+  _ = redisClient.Set(key, time, 0)
 
   for _, connection := range connections[client] {
-    connection <- []byte(strconv.FormatInt(time, 10))
+    connection <- time
   }
 
   w.WriteHeader(http.StatusOK)