websocket support

go.mod

@@ -7,6 +7,7 @@ require (
 	github.com/caarlos0/env/v11 v11.2.2
 	github.com/gleich/lumber/v3 v3.0.2
 	github.com/go-chi/chi/v5 v5.1.0
+	github.com/gorilla/websocket v1.5.3
 	github.com/joho/godotenv v1.5.1
 	github.com/minio/minio-go/v7 v7.0.81
 	github.com/prometheus/client_golang v1.20.5

go.sum

@@ -28,6 +28,8 @@ github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
 github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
 github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
 github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
+github.com/gorilla/websocket v1.5.3 h1:saDtZ6Pbx/0u+bgYQ3q96pZgCzfhKXGPqt7kZ72aNNg=
+github.com/gorilla/websocket v1.5.3/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=
 github.com/joho/godotenv v1.5.1 h1:7eLL/+HRGLY0ldzfGMeQkb7vMd0as4CfYvUVzLqw0N0=
 github.com/joho/godotenv v1.5.1/go.mod h1:f4LDr5Voq0i2e/R5DDNOoa2zzDfwtkZa6DnEwAbqwq4=
 github.com/klauspost/compress v1.17.11 h1:In6xLpyWOi1+C7tXUUWv2ot1QvBjxevKAaI6IXrJmUc=

internal/cache/cache.go

@@ -14,18 +14,22 @@ import (
 	"github.com/gleich/lcp-v2/internal/metrics"
 	"github.com/gleich/lcp-v2/internal/secrets"
 	"github.com/gleich/lumber/v3"
+	"github.com/gorilla/websocket"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promauto"
 )
 
 type Cache[T any] struct {
-	name           string
-	mutex          sync.RWMutex
-	data           T
-	updated        time.Time
-	updateCounter  prometheus.Counter
-	requestCounter prometheus.Counter
-	filePath       string
+	name            string
+	dataMutex       sync.RWMutex
+	data            T
+	updated         time.Time
+	updateCounter   prometheus.Counter
+	requestCounter  prometheus.Counter
+	filePath        string
+	wsConnPool      map[*websocket.Conn]bool
+	wsConnPoolMutex sync.Mutex
+	wsUpgrader      websocket.Upgrader
 }
 
 func NewCache[T any](name string, data T) *Cache[T] {
@@ -39,7 +43,9 @@ func NewCache[T any](name string, data T) *Cache[T] {
 			Name: fmt.Sprintf("cache_%s_requests", name),
 			Help: fmt.Sprintf(`The total number of times the cache "%s" has been requested`, name),
 		}),
-		filePath: filepath.Join(secrets.SECRETS.CacheFolder, fmt.Sprintf("%s.json", name)),
+		filePath:   filepath.Join(secrets.SECRETS.CacheFolder, fmt.Sprintf("%s.json", name)),
+		wsConnPool: make(map[*websocket.Conn]bool),
+		wsUpgrader: websocket.Upgrader{},
 	}
 	cache.loadFromFile()
 	cache.Update(data)
@@ -58,10 +64,10 @@ func (c *Cache[T]) ServeHTTP() http.HandlerFunc {
 			w.WriteHeader(http.StatusUnauthorized)
 			return
 		}
-		c.mutex.RLock()
+		c.dataMutex.RLock()
 		w.Header().Set("Content-Type", "application/json")
 		err := json.NewEncoder(w).Encode(cacheData[T]{Data: c.data, Updated: c.updated})
-		c.mutex.RUnlock()
+		c.dataMutex.RUnlock()
 		c.requestCounter.Inc()
 		if err != nil {
 			lumber.Error(err, "failed to write data")
@@ -74,7 +80,7 @@ func (c *Cache[T]) ServeHTTP() http.HandlerFunc {
 // Update the given cache
 func (c *Cache[T]) Update(data T) {
 	var updated bool
-	c.mutex.Lock()
+	c.dataMutex.Lock()
 	old, err := json.Marshal(c.data)
 	if err != nil {
 		lumber.Error(err, "failed to json marshal old data")
@@ -90,12 +96,18 @@ func (c *Cache[T]) Update(data T) {
 		c.updated = time.Now()
 		updated = true
 	}
-	c.mutex.Unlock()
+	c.dataMutex.Unlock()
+
 	if updated {
 		c.updateCounter.Inc()
 		metrics.CacheUpdates.Inc()
 		c.persistToFile()
-		lumber.Done(strings.ToUpper(c.name), "cache updated")
+		connectionsUpdated := c.broadcastUpdate()
+		lumber.Done(
+			strings.ToUpper(c.name),
+			"cache updated;",
+			"broadcasted to", connectionsUpdated, "websocket connections",
+		)
 	}
 }
 

internal/cache/websockets.go

@@ -0,0 +1,62 @@
+package cache
+
+import (
+	"net/http"
+
+	"github.com/gleich/lumber/v3"
+	"github.com/gorilla/websocket"
+)
+
+// Handle websocket connections
+func (c *Cache[T]) ServeWS() http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		conn, err := c.wsUpgrader.Upgrade(w, r, nil)
+		if err != nil {
+			lumber.Error(err, "failed to upgrade connection to websocket")
+			return
+		}
+		c.wsConnPoolMutex.Lock()
+		c.wsConnPool[conn] = true
+		c.wsConnPoolMutex.Unlock()
+
+		// sending initial data
+		c.dataMutex.RLock()
+		err = conn.WriteJSON(c.data)
+		c.dataMutex.RUnlock()
+		if err != nil {
+			lumber.Error(err, "failed to write initial cache data for", c.name)
+			c.removeConnection(conn)
+			return
+		}
+
+		// spawning goroutine to handle connection
+		go func() {
+			defer c.removeConnection(conn)
+		}()
+	}
+}
+
+func (c *Cache[T]) broadcastUpdate() int {
+	c.dataMutex.RLock()
+	d := c.data
+	c.dataMutex.RUnlock()
+
+	updatedConnections := 0
+	for conn := range c.wsConnPool {
+		err := conn.WriteJSON(d)
+		if err != nil {
+			lumber.Error(err, "failed to broadcast update to client")
+			c.removeConnection(conn)
+		} else {
+			updatedConnections++
+		}
+	}
+	return updatedConnections
+}
+
+func (c *Cache[T]) removeConnection(conn *websocket.Conn) {
+	c.wsConnPoolMutex.Lock()
+	delete(c.wsConnPool, conn)
+	c.wsConnPoolMutex.Unlock()
+	conn.Close()
+}