From ccc64e545466c34c7f919eded0dd536e974c2935 Mon Sep 17 00:00:00 2001
From: Jozef Kralik <jozef.kralik@plgd.dev>
Date: Wed, 14 Jul 2021 16:10:42 +0200
Subject: [PATCH] fix write concurrency to socket

according to https://pkg.go.dev/github.com/gorilla/websocket#hdr-Concurrency, is not supported by WriteMessage.

fixes issue with nginx proxy: SSL routines:ssl3_get_record:decryption failed or bad record mac
---
 wsproxy/websocket_proxy.go | 44 ++++++++++++++++++++++----------------
 1 file changed, 26 insertions(+), 18 deletions(-)

diff --git a/wsproxy/websocket_proxy.go b/wsproxy/websocket_proxy.go
index 7092162..601b6be 100644
--- a/wsproxy/websocket_proxy.go
+++ b/wsproxy/websocket_proxy.go
@@ -261,28 +261,39 @@ func (p *Proxy) proxy(w http.ResponseWriter, r *http.Request) {
 			}
 		}
 	}()
-	// ping write loop
-	if p.pingInterval > 0 && p.pingWait > 0 && p.pongWait > 0 {
-		go func() {
+
+	// write loop -- take bytes from http and write to websocket
+	dataWriteChan := make(chan []byte, 32)
+	go func() {
+		var pingChan <-chan time.Time
+		if p.pingInterval > 0 && p.pingWait > 0 && p.pongWait > 0 {
 			ticker := time.NewTicker(p.pingInterval)
+			pingChan = ticker.C
 			defer func() {
 				ticker.Stop()
 				conn.Close()
 			}()
-			for {
-				select {
-				case <-ctx.Done():
-					p.logger.Debugln("ping loop done")
+		} else {
+			pingChan = make(chan time.Time)
+		}
+		for {
+			select {
+			case <-ctx.Done():
+				p.logger.Debugln("write loop done")
+				return
+			case <-pingChan:
+				if err := conn.WriteMessage(websocket.PingMessage, nil); err != nil {
+					return
+				}
+			case data := <-dataWriteChan:
+				if err = conn.WriteMessage(websocket.TextMessage, data); err != nil {
+					p.logger.Warnln("[write] error writing websocket message:", err)
 					return
-				case <-ticker.C:
-					conn.SetWriteDeadline(time.Now().Add(p.pingWait))
-					if err := conn.WriteMessage(websocket.PingMessage, nil); err != nil {
-						return
-					}
 				}
 			}
-		}()
-	}
+		}
+	}()
+
 	// write loop -- take messages from response and write to websocket
 	scanner := bufio.NewScanner(responseBodyR)
 
@@ -299,10 +310,7 @@ func (p *Proxy) proxy(w http.ResponseWriter, r *http.Request) {
 			continue
 		}
 		p.logger.Debugln("[write] scanned", scanner.Text())
-		if err = conn.WriteMessage(websocket.TextMessage, scanner.Bytes()); err != nil {
-			p.logger.Warnln("[write] error writing websocket message:", err)
-			return
-		}
+		dataWriteChan <- scanner.Bytes()
 	}
 	if err := scanner.Err(); err != nil {
 		p.logger.Warnln("scanner err:", err)