From a0dccea9a301fcd2c1ffee6242fc8a459176d149 Mon Sep 17 00:00:00 2001
From: Michael Geers <michael@geers.tv>
Date: Sun, 8 Mar 2026 12:32:23 +0100
Subject: [PATCH] Websocket: split welcome message (#27967)

---
 server/socket.go | 32 +++++++++++++++++++++++++-------
 1 file changed, 25 insertions(+), 7 deletions(-)

diff --git a/server/socket.go b/server/socket.go
index 40d042051..8b5a9c128 100644
--- a/server/socket.go
+++ b/server/socket.go
@@ -52,10 +52,11 @@ func (h *SocketHub) ServeWebsocket(w http.ResponseWriter, r *http.Request) {
 		InsecureSkipVerify: true,
 	}
 
-	// https://github.com/nhooyr/websocket/issues/218
+	// Safari deflate message compression is broken, enable for others
+	// see: https://github.com/gorilla/websocket/issues/731
 	ua := strings.ToLower(r.Header.Get("User-Agent"))
-	if strings.Contains(ua, "safari") && !strings.Contains(ua, "chrome") && !strings.Contains(ua, "android") {
-		acceptOptions.CompressionMode = websocket.CompressionDisabled
+	if strings.Contains(ua, "chrome") || strings.Contains(ua, "firefox") {
+		acceptOptions.CompressionMode = websocket.CompressionContextTakeover
 	}
 
 	conn, err := websocket.Accept(w, r, acceptOptions)
@@ -88,6 +89,7 @@ func (h *SocketHub) subscribe(ctx context.Context, conn *websocket.Conn) error {
 		select {
 		case msg := <-s.send:
 			if err := writeTimeout(ctx, socketWriteTimeout, conn, msg); err != nil {
+				log.TRACE.Printf("ws write error: %v, len: %.1fkB, msg: %s", err, float64(len(msg))/1024, msg[:min(len(msg), 20)])
 				return err
 			}
 		case <-ctx.Done():
@@ -112,6 +114,7 @@ func (h *SocketHub) deleteSubscriber(s *socketSubscriber) {
 
 func (h *SocketHub) welcome(subscriber *socketSubscriber, params []util.Param) {
 	msg := make(map[string]json.RawMessage, len(params))
+	sharders := make(map[string]util.Sharder)
 
 	for _, p := range params {
 		k := p.Key
@@ -119,13 +122,28 @@ func (h *SocketHub) welcome(subscriber *socketSubscriber, params []util.Param) {
 			k = "loadpoints." + p.UniqueID()
 		}
 
-		msg[k] = json.RawMessage(socketEncode(p.Val))
+		// Sharder values are split into shards and sent as a separate message
+		if sharder, ok := (p.Val).(util.Sharder); ok {
+			sharders[k] = sharder
+		} else {
+			msg[k] = json.RawMessage(socketEncode(p.Val))
+		}
 	}
 
-	b, _ := json.Marshal(msg)
+	// send compact state first, then potentially large sharded data
+	if b, err := json.Marshal(msg); err == nil {
+		subscriber.send <- b
+	}
 
-	// should not block
-	subscriber.send <- b
+	for k, sharder := range sharders {
+		for key, val := range sharder.AllShards() {
+			if b, err := json.Marshal(map[string]json.RawMessage{
+				k + "." + key: json.RawMessage(socketEncode(val)),
+			}); err == nil {
+				subscriber.send <- b
+			}
+		}
+	}
 }
 
 func (h *SocketHub) broadcast(p util.Param) {