From 7aa684a354b7f14fb4d1066f0d93399fe25e1806 Mon Sep 17 00:00:00 2001
From: Gaukas Wang <i@gauk.as>
Date: Thu, 30 Mar 2023 09:14:55 -0600
Subject: [PATCH] fix: PSK extension w/o session cache crashing (#177)

Fixes a bug causing client to crash (SIGSEGV) WHEN PSK extension is set with empty session cache AND server sends HelloRetryRequest.
---
 u_tls_extensions.go | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/u_tls_extensions.go b/u_tls_extensions.go
index 3bc8826d..4d3b07bb 100644
--- a/u_tls_extensions.go
+++ b/u_tls_extensions.go
@@ -1859,6 +1859,9 @@ type FakePreSharedKeyExtension struct {
 }
 
 func (e *FakePreSharedKeyExtension) writeToUConn(uc *UConn) error {
+	if session, ok := uc.config.ClientSessionCache.Get(clientSessionCacheKey(uc.conn.RemoteAddr(), uc.config)); !ok || session == nil {
+		return nil // don't write the extension if there is no session
+	}
 	uc.HandshakeState.Hello.PskIdentities = e.PskIdentities
 	uc.HandshakeState.Hello.PskBinders = e.PskBinders
 	return nil