From 00d475bc7e44abe90944b399efc65d66a8691596 Mon Sep 17 00:00:00 2001
From: cpq <valenok@gmail.com>
Date: Thu, 21 Sep 2023 12:35:47 +0100
Subject: [PATCH] Address https://github.com/cesanta/mongoose/discussions/2305
 - bind to v6 only / v6 and v4

---
 mongoose.c   | 3 ++-
 mongoose.h   | 4 ++++
 src/config.h | 4 ++++
 src/sock.c   | 3 ++-
 4 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/mongoose.c b/mongoose.c
index ec134faea8..22bb4448b6 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -6062,7 +6062,8 @@ bool mg_open_listener(struct mg_connection *c, const char *url) {
       // won't work! (setsockopt will return EINVAL)
       MG_ERROR(("setsockopt(SO_REUSEADDR): %d", MG_SOCK_ERR(rc)));
 #endif
-#if defined(IPV6_V6ONLY)
+#if MG_IPV6_V6ONLY
+      // Bind only to the V6 address, not V4 address on this port
     } else if (c->loc.is_ip6 &&
                (rc = setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, (char *) &on,
                                 sizeof(on))) != 0) {
diff --git a/mongoose.h b/mongoose.h
index df3d236dd2..90268f4db9 100644
--- a/mongoose.h
+++ b/mongoose.h
@@ -709,6 +709,10 @@ struct timeval {
 #define MG_ENABLE_IPV6 0
 #endif
 
+#ifndef MG_IPV6_V6ONLY
+#define MG_IPV6_V6ONLY 0  // IPv6 socket binds only to V6, not V4 address
+#endif
+
 #ifndef MG_ENABLE_MD5
 #define MG_ENABLE_MD5 1
 #endif
diff --git a/src/config.h b/src/config.h
index a1eff241ec..f69da6571b 100644
--- a/src/config.h
+++ b/src/config.h
@@ -44,6 +44,10 @@
 #define MG_ENABLE_IPV6 0
 #endif
 
+#ifndef MG_IPV6_V6ONLY
+#define MG_IPV6_V6ONLY 0  // IPv6 socket binds only to V6, not V4 address
+#endif
+
 #ifndef MG_ENABLE_MD5
 #define MG_ENABLE_MD5 1
 #endif
diff --git a/src/sock.c b/src/sock.c
index 089714c754..ff4d2dff87 100644
--- a/src/sock.c
+++ b/src/sock.c
@@ -212,7 +212,8 @@ bool mg_open_listener(struct mg_connection *c, const char *url) {
       // won't work! (setsockopt will return EINVAL)
       MG_ERROR(("setsockopt(SO_REUSEADDR): %d", MG_SOCK_ERR(rc)));
 #endif
-#if defined(IPV6_V6ONLY)
+#if MG_IPV6_V6ONLY
+      // Bind only to the V6 address, not V4 address on this port
     } else if (c->loc.is_ip6 &&
                (rc = setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, (char *) &on,
                                 sizeof(on))) != 0) {