From 2b866fdcb4a69285306a4db7910742b5525bc79f Mon Sep 17 00:00:00 2001
From: Sam Rose <samwho@lbak.co.uk>
Date: Thu, 25 Jul 2019 19:30:37 +0100
Subject: [PATCH] Serialise websocket writes as per
 https://godoc.org/github.com/gorilla/websocket#hdr-Concurrency

---
 client.go | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/client.go b/client.go
index 22af1f2..94a1aa0 100644
--- a/client.go
+++ b/client.go
@@ -9,6 +9,7 @@ import (
 	"net/url"
 	"os"
 	"os/signal"
+	"sync"
 	"time"
 
 	"github.com/gorilla/websocket"
@@ -26,12 +27,13 @@ func Log() *log.Logger {
 type EventHandler func(ctx context.Context, client *Client, event Event) error
 
 type Client struct {
-	ctx      context.Context
-	params   RegistrationParams
-	c        *websocket.Conn
-	actions  map[string]*Action
-	handlers map[string][]EventHandler
-	done     chan struct{}
+	ctx       context.Context
+	params    RegistrationParams
+	c         *websocket.Conn
+	actions   map[string]*Action
+	handlers  map[string][]EventHandler
+	done      chan struct{}
+	sendMutex sync.Mutex
 }
 
 func NewClient(ctx context.Context, params RegistrationParams) *Client {
@@ -140,6 +142,8 @@ func (client *Client) register(params RegistrationParams) error {
 
 func (client *Client) send(event Event) error {
 	j, _ := json.Marshal(event)
+	client.sendMutex.Lock()
+	defer client.sendMutex.Unlock()
 	logger.Printf("sending message: %v\n", string(j))
 	return client.c.WriteJSON(event)
 }