From 0df93bfab7c3132a333f3e6b2013c4ba1945eaa9 Mon Sep 17 00:00:00 2001
From: Vladimir Dubrovin <3proxy@3proxy.ru>
Date: Wed, 26 Aug 2026 16:55:37 +0300
Subject: [PATCH] Let a Windows UDP service bind the socket it answers from

A UDP service on Windows binds a second socket to the address it listens on,
so a reply leaves the port the client sent to. Windows only allows that when
both sockets ask for it, and the listening socket was never asked, so the
bind failed and dnspr answered nothing at all on Windows.

Ask for it on the listening socket of a UDP service, and there only: the
reason it is withheld otherwise, that another local process could take a
listening port, is unchanged for everything else.
---
 src/proxymain.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/proxymain.c b/src/proxymain.c
index a09bcaa..8b3f141 100644
--- a/src/proxymain.c
+++ b/src/proxymain.c
@@ -830,6 +830,14 @@ int MODULEMAINFUNC (int argc, char** argv){
 #ifndef _WIN32
 		opt = 1;
 		if(srv.so._setsockopt(srv.so.state, sock, SOL_SOCKET, SO_REUSEADDR, (char *)&opt, sizeof(int)))perror("setsockopt()");
+#else
+		/* A UDP service on Windows answers from a second socket bound to
+		   the address it listens on, and Windows only allows that bind
+		   when both sockets ask for it. */
+		if(isudp){
+			opt = 1;
+			if(srv.so._setsockopt(srv.so.state, sock, SOL_SOCKET, SO_REUSEADDR, (char *)&opt, sizeof(int)))perror("setsockopt()");
+		}
 #endif
 #ifdef SO_REUSEPORT
 		opt = 1;