From 32ca0fba5108d0dc2c7415f36e55f031d5a0562e Mon Sep 17 00:00:00 2001
From: bndw <ben@bdw.to>
Date: Sat, 14 Feb 2026 21:53:14 -0800
Subject: feat: add rate limiting to WebSocket connections

WebSocket clients were completely unprotected from abuse. Add RateLimiter
interface to WebSocket handler and enforce limits on EVENT and REQ messages.

- Add RateLimiter interface with Allow(identifier, method) method
- Track client IP in connState (proxy-aware via X-Forwarded-For)
- Check rate limits in handleEvent and handleReq
- Use authenticated pubkey as identifier, fallback to IP
- Share same rate limiter instance with gRPC
- Add getClientIP() helper that checks proxy headers first

Critical security fix for production deployment. Without this, any client
could spam unlimited events/subscriptions via WebSocket.
---
 internal/handler/websocket/handler.go | 54 ++++++++++++++++++++++++++++++++++-
 1 file changed, 53 insertions(+), 1 deletion(-)

(limited to 'internal/handler/websocket/handler.go')

diff --git a/internal/handler/websocket/handler.go b/internal/handler/websocket/handler.go
index 8bd246d..a7b73ec 100644
--- a/internal/handler/websocket/handler.go
+++ b/internal/handler/websocket/handler.go
@@ -31,6 +31,10 @@ type MetricsRecorder interface {
 	SetActiveSubscriptions(count int)
 }
 
+type RateLimiter interface {
+	Allow(identifier, method string) bool
+}
+
 type AuthConfig struct {
 	ReadEnabled         bool
 	WriteEnabled        bool
@@ -41,6 +45,7 @@ type AuthConfig struct {
 type connState struct {
 	authenticatedPubkey string
 	authChallenge       string
+	clientIP            string
 }
 
 type Handler struct {
@@ -48,6 +53,7 @@ type Handler struct {
 	auth       AuthStore
 	subs       *subscription.Manager
 	metrics    MetricsRecorder
+	limiter    RateLimiter
 	authConfig *AuthConfig
 	indexData  IndexData
 }
@@ -67,6 +73,10 @@ func (h *Handler) SetAuth(a AuthStore) {
 	h.auth = a
 }
 
+func (h *Handler) SetRateLimiter(l RateLimiter) {
+	h.limiter = l
+}
+
 func (h *Handler) SetAuthConfig(cfg *AuthConfig) {
 	h.authConfig = cfg
 }
@@ -106,7 +116,9 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 
 	ctx := r.Context()
 	clientSubs := make(map[string]*subscription.Subscription)
-	state := &connState{}
+	state := &connState{
+		clientIP: getClientIP(r),
+	}
 
 	defer func() {
 		count := len(clientSubs)
@@ -224,6 +236,17 @@ func (h *Handler) handleEvent(ctx context.Context, conn *websocket.Conn, raw []j
 		return nil
 	}
 
+	// Rate limiting - use pubkey if authenticated, otherwise IP
+	if h.limiter != nil {
+		identifier := state.authenticatedPubkey
+		if identifier == "" {
+			identifier = state.clientIP
+		}
+		if !h.limiter.Allow(identifier, "EVENT") {
+			return fmt.Errorf("rate limit exceeded")
+		}
+	}
+
 	var event nostr.Event
 	if err := json.Unmarshal(raw[1], &event); err != nil {
 		return fmt.Errorf("invalid event: %w", err)
@@ -286,6 +309,17 @@ func (h *Handler) handleReq(ctx context.Context, conn *websocket.Conn, raw []jso
 		return nil
 	}
 
+	// Rate limiting - use pubkey if authenticated, otherwise IP
+	if h.limiter != nil {
+		identifier := state.authenticatedPubkey
+		if identifier == "" {
+			identifier = state.clientIP
+		}
+		if !h.limiter.Allow(identifier, "REQ") {
+			return fmt.Errorf("rate limit exceeded")
+		}
+	}
+
 	var subID string
 	if err := json.Unmarshal(raw[1], &subID); err != nil {
 		return fmt.Errorf("invalid subscription ID")
@@ -453,3 +487,21 @@ func (h *Handler) handleAuth(ctx context.Context, conn *websocket.Conn, raw []js
 	h.sendOK(ctx, conn, authEvent.ID, true, "")
 	return nil
 }
+
+// getClientIP extracts the real client IP from the HTTP request.
+// Checks X-Forwarded-For and X-Real-IP headers first (for reverse proxy setups),
+// then falls back to RemoteAddr.
+func getClientIP(r *http.Request) string {
+	// Check X-Forwarded-For header (set by reverse proxies like Caddy/nginx)
+	if xff := r.Header.Get("X-Forwarded-For"); xff != "" {
+		return xff
+	}
+
+	// Check X-Real-IP header
+	if xri := r.Header.Get("X-Real-IP"); xri != "" {
+		return xri
+	}
+
+	// Fall back to RemoteAddr (direct connection or proxy IP)
+	return r.RemoteAddr
+}
-- 
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