From 3d404919cd69acd36985b35d7268d52dcefc44fb Mon Sep 17 00:00:00 2001
From: Amir Khan <a.khan@psiphon.ca>
Date: Thu, 7 Nov 2024 11:40:31 -0500
Subject: [PATCH] Fixed KeySharesParams reset on subsequent ApplyPreset calls

* This fixes an issue where servers that selected a key_share other than
  CurveP256 would cause TLS handshake to fail. This is because
  the precomputed key_shares are thrown away and not replaced if
  ApplyPreset is called more than once.
---
 u_parrots.go | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/u_parrots.go b/u_parrots.go
index 86b8a19e..e55cd807 100644
--- a/u_parrots.go
+++ b/u_parrots.go
@@ -2636,7 +2636,9 @@ func (uconn *UConn) ApplyPreset(p *ClientHelloSpec) error {
 	} else if kemKey, ok := clientKeySharePrivate.(*kemPrivateKey); ok {
 		uconn.HandshakeState.State13.KEMKey = kemKey.ToPublic()
 	}
-	uconn.HandshakeState.State13.KeySharesParams = NewKeySharesParameters()
+	if uconn.HandshakeState.State13.KeySharesParams == nil {
+		uconn.HandshakeState.State13.KeySharesParams = NewKeySharesParameters()
+	}
 	hello := uconn.HandshakeState.Hello
 
 	switch len(hello.Random) {