From 172e7890b98875999b66c218fc109a533d19dc7d Mon Sep 17 00:00:00 2001
From: fiatjaf <fiatjaf@gmail.com>
Date: Sat, 28 Mar 2026 10:47:25 -0300
Subject: [PATCH] khatru: use a channelmutex so we can fail to lock on
 addListener() if there's a disconnect.

---
 go.mod             | 1 +
 go.sum             | 2 ++
 khatru/listener.go | 8 ++++++--
 khatru/relay.go    | 8 +++++---
 4 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/go.mod b/go.mod
index 95864b5..4baecdc 100644
--- a/go.mod
+++ b/go.mod
@@ -40,6 +40,7 @@ require (
 )
 
 require (
+	fiatjaf.com/lib v0.3.6
 	github.com/dgraph-io/ristretto/v2 v2.3.0
 	github.com/go-git/go-git/v5 v5.16.3
 	github.com/sivukhin/godjot v1.0.6
diff --git a/go.sum b/go.sum
index b4ececd..788c24b 100644
--- a/go.sum
+++ b/go.sum
@@ -1,3 +1,5 @@
+fiatjaf.com/lib v0.3.6 h1:GRZNSxHI2EWdjSKVuzaT+c0aifLDtS16SzkeJaHyJfY=
+fiatjaf.com/lib v0.3.6/go.mod h1:UlHaZvPHj25PtKLh9GjZkUHRmQ2xZ8Jkoa4VRaLeeQ8=
 github.com/FactomProject/basen v0.0.0-20150613233007-fe3947df716e h1:ahyvB3q25YnZWly5Gq1ekg6jcmWaGj/vG/MhF4aisoc=
 github.com/FactomProject/basen v0.0.0-20150613233007-fe3947df716e/go.mod h1:kGUqhHd//musdITWjFvNTHn90WG9bMLBEPQZ17Cmlpw=
 github.com/FactomProject/btcutilecc v0.0.0-20130527213604-d3a63a5752ec h1:1Qb69mGp/UtRPn422BH4/Y4Q3SLUrD9KHuDkm8iodFc=
diff --git a/khatru/listener.go b/khatru/listener.go
index 579abbc..7a35ce1 100644
--- a/khatru/listener.go
+++ b/khatru/listener.go
@@ -40,8 +40,12 @@ func (rl *Relay) addListener(
 	filter nostr.Filter,
 	cancel context.CancelCauseFunc,
 ) {
-	rl.clientsMutex.Lock()
-	defer rl.clientsMutex.Unlock()
+	select {
+	case <-rl.clientsMutex.C():
+		defer rl.clientsMutex.Unlock()
+	case <-ws.Context.Done():
+		return
+	}
 
 	if specs, ok := rl.clients[ws]; ok /* this will always be true unless client has disconnected very rapidly */ {
 		idx := len(subrelay.listeners)
diff --git a/khatru/relay.go b/khatru/relay.go
index f395501..0cc150e 100644
--- a/khatru/relay.go
+++ b/khatru/relay.go
@@ -8,9 +8,9 @@ import (
 	"os"
 	"strconv"
 	"strings"
-	"sync"
 	"time"
 
+	"fiatjaf.com/lib/channelmutex"
 	"fiatjaf.com/nostr"
 	"fiatjaf.com/nostr/eventstore"
 	"fiatjaf.com/nostr/nip11"
@@ -39,7 +39,9 @@ func NewRelay() *Relay {
 			CheckOrigin:     func(r *http.Request) bool { return true },
 		},
 
-		clients:   make(map[*WebSocket][]listenerSpec, 100),
+		clients:      make(map[*WebSocket][]listenerSpec, 100),
+		clientsMutex: channelmutex.New(),
+
 		listeners: make([]listener, 0, 100),
 
 		serveMux: &http.ServeMux{},
@@ -107,7 +109,7 @@ type Relay struct {
 	// also used for keeping track of who is listening to what
 	clients      map[*WebSocket][]listenerSpec
 	listeners    []listener
-	clientsMutex sync.Mutex
+	clientsMutex *channelmutex.Mutex
 
 	// set this to true to support negentropy
 	Negentropy bool