From d43255885cd84d3ed1f7e70a4b00eae64eb7a7de Mon Sep 17 00:00:00 2001
From: ifedorenko <igor@ifedorenko.com>
Date: Thu, 20 Feb 2020 19:58:40 -0500
Subject: [PATCH] Serialize websocket writes with a mutex (#256)

Fixes #241

Signed-off-by: Igor Fedorenko <igor@ifedorenko.com>
---
 internal/api/websocket.go | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/internal/api/websocket.go b/internal/api/websocket.go
index 2e0b80b86..40055f76d 100644
--- a/internal/api/websocket.go
+++ b/internal/api/websocket.go
@@ -33,7 +33,7 @@ var wsAuth = struct {
 	mutex         sync.RWMutex
 }{authenticated: make(map[string]bool)}
 
-func wsReader(ws *websocket.Conn, connId string, conf *config.Config) {
+func wsReader(ws *websocket.Conn, writeMutex *sync.Mutex, connId string, conf *config.Config) {
 	defer ws.Close()
 
 	ws.SetReadLimit(512)
@@ -61,17 +61,19 @@ func wsReader(ws *websocket.Conn, connId string, conf *config.Config) {
 				wsAuth.authenticated[connId] = true
 				wsAuth.mutex.Unlock()
 
+				writeMutex.Lock()
 				ws.SetWriteDeadline(time.Now().Add(30 * time.Second))
 
 				if err := ws.WriteJSON(gin.H{"event": "config.updated", "data": event.Data(conf.ClientConfig())}); err != nil {
 					log.Error(err)
 				}
+				writeMutex.Unlock()
 			}
 		}
 	}
 }
 
-func wsWriter(ws *websocket.Conn, connId string) {
+func wsWriter(ws *websocket.Conn, writeMutex *sync.Mutex, connId string) {
 	pingTicker := time.NewTicker(15 * time.Second)
 	s := event.Subscribe("log.*", "notify.*", "index.*", "upload.*", "import.*", "config.*", "count.*", "photos.*", "albums.*", "labels.*")
 
@@ -98,12 +100,15 @@ func wsWriter(ws *websocket.Conn, connId string) {
 			wsAuth.mutex.RUnlock()
 
 			if auth {
+				writeMutex.Lock()
 				ws.SetWriteDeadline(time.Now().Add(30 * time.Second))
 
 				if err := ws.WriteJSON(gin.H{"event": msg.Name, "data": msg.Fields}); err != nil {
+					writeMutex.Unlock()
 					log.Debug(err)
 					return
 				}
+				writeMutex.Unlock()
 			}
 		}
 	}
@@ -131,6 +136,8 @@ func Websocket(router *gin.RouterGroup, conf *config.Config) {
 			return
 		}
 
+		var writeMutex sync.Mutex
+
 		defer ws.Close()
 
 		connId := rnd.UUID()
@@ -143,8 +150,8 @@ func Websocket(router *gin.RouterGroup, conf *config.Config) {
 
 		log.Debug("websocket: connected")
 
-		go wsWriter(ws, connId)
+		go wsWriter(ws, &writeMutex, connId)
 
-		wsReader(ws, connId, conf)
+		wsReader(ws, &writeMutex, connId, conf)
 	})
 }