From f50b7b0f8dcb93785c11a71078b5e10b21625253 Mon Sep 17 00:00:00 2001
From: fiatjaf <fiatjaf@gmail.com>
Date: Thu, 16 Apr 2026 11:56:33 -0300
Subject: [PATCH] khatru: list clients and client details.

---
 khatru/relay.go     | 86 +++++++++++++++++++++++++++++++++++++++++++++
 khatru/websocket.go | 10 ++++++
 2 files changed, 96 insertions(+)

diff --git a/khatru/relay.go b/khatru/relay.go
index 9e22b0b..107137b 100644
--- a/khatru/relay.go
+++ b/khatru/relay.go
@@ -2,6 +2,8 @@ package khatru
 
 import (
 	"context"
+	"encoding/base64"
+	"encoding/binary"
 	"iter"
 	"log"
 	"net/http"
@@ -9,6 +11,7 @@ import (
 	"strconv"
 	"strings"
 	"time"
+	"unsafe"
 
 	"fiatjaf.com/lib/channelmutex"
 	"fiatjaf.com/nostr"
@@ -212,6 +215,89 @@ func (rl *Relay) Stats() (clients, listeners int) {
 	return len(rl.clients), listeners
 }
 
+type ClientInfo struct {
+	ID                string
+	IP                string
+	UserAgent         string
+	Origin            string
+	Authenticated     []nostr.PubKey
+	SubscriptionCount int
+}
+
+type SubscriptionInfo struct {
+	ID     string
+	Filter nostr.Filter
+}
+
+type ClientSnapshot struct {
+	ClientInfo
+	Subscriptions []SubscriptionInfo
+}
+
+func (rl *Relay) ListClients() []ClientInfo {
+	rl.clientsMutex.Lock()
+	defer rl.clientsMutex.Unlock()
+
+	clients := make([]ClientInfo, 0, len(rl.clients))
+	for ws, specs := range rl.clients {
+		clients = append(clients, ClientInfo{
+			ID:                ws.GetID(),
+			IP:                GetIPFromRequest(ws.Request),
+			UserAgent:         ws.Request.UserAgent(),
+			Origin:            ws.Request.Header.Get("Origin"),
+			Authenticated:     ws.AuthedPublicKeys,
+			SubscriptionCount: len(specs),
+		})
+	}
+
+	return clients
+}
+
+func (rl *Relay) GetClientSnapshot(id string) (ClientSnapshot, bool) {
+	rl.clientsMutex.Lock()
+	defer rl.clientsMutex.Unlock()
+
+	ptrn, err := base64.RawURLEncoding.DecodeString(id)
+	if err != nil {
+		return ClientSnapshot{}, false
+	}
+	ptr := binary.LittleEndian.Uint64(ptrn)
+
+	// DANGEROUS:
+	// don't try to do anything with this `ws` object before we confirm it exists by checking the rl.clients map
+	ws := (*WebSocket)(unsafe.Pointer(uintptr(ptr)))
+	specs, ok := rl.clients[ws]
+	if !ok {
+		return ClientSnapshot{}, false
+	}
+
+	details := ClientSnapshot{
+		ClientInfo: ClientInfo{
+			ID:                id,
+			IP:                GetIPFromRequest(ws.Request),
+			UserAgent:         ws.Request.UserAgent(),
+			Origin:            ws.Request.Header.Get("Origin"),
+			Authenticated:     ws.AuthedPublicKeys,
+			SubscriptionCount: len(specs),
+		},
+		Subscriptions: make([]SubscriptionInfo, 0, len(specs)),
+	}
+
+	for _, spec := range specs {
+		filter := nostr.Filter{}
+		if sub, ok := rl.dispatcher.subscriptions.Load(spec.ssid); ok {
+			filter = sub.filter
+		}
+
+		details.Subscriptions = append(details.Subscriptions, SubscriptionInfo{
+			ID:     spec.sid,
+			Filter: filter,
+		})
+	}
+
+	return details, true
+}
+
 func (rl *Relay) Router() *http.ServeMux {
 	return rl.serveMux
 }
diff --git a/khatru/websocket.go b/khatru/websocket.go
index 40484c6..f90f235 100644
--- a/khatru/websocket.go
+++ b/khatru/websocket.go
@@ -2,9 +2,12 @@ package khatru
 
 import (
 	"context"
+	"encoding/base64"
+	"encoding/binary"
 	"fmt"
 	"net/http"
 	"sync"
+	"unsafe"
 
 	"fiatjaf.com/nostr"
 	"github.com/fasthttp/websocket"
@@ -31,6 +34,13 @@ type WebSocket struct {
 	negentropySessions *xsync.MapOf[string, *NegentropySession]
 }
 
+func (ws *WebSocket) GetID() string {
+	ptr := uintptr(unsafe.Pointer(ws))
+	var id [8]byte
+	binary.LittleEndian.PutUint64(id[:], uint64(ptr))
+	return base64.RawURLEncoding.EncodeToString(id[:])
+}
+
 func (ws *WebSocket) WriteJSON(any any) error {
 	if ws == nil {
 		return fmt.Errorf("connection doesn't exist")