From 265f4eb61e1f494eb78071c13e8c061f63132f67 Mon Sep 17 00:00:00 2001
From: Philipp Schafft <phschafft@de.loewenfelsen.net>
Date: Mon, 7 Mar 2022 09:49:12 +0000
Subject: [PATCH] Feature: Added a way to prefer IPv6 for binding sockets

---
 net/sock.c | 51 +++++++++++++++++++++++++++++++++------------------
 net/sock.h |  2 +-
 2 files changed, 34 insertions(+), 19 deletions(-)

diff --git a/net/sock.c b/net/sock.c
index 28c4e31..889d09a 100644
--- a/net/sock.c
+++ b/net/sock.c
@@ -712,7 +712,7 @@ sock_t sock_connect_wto_bind (const char *hostname, int port, const char *bnd, i
 }
 
 
-sock_t sock_get_server_socket (int port, const char *sinterface)
+sock_t sock_get_server_socket (int port, const char *sinterface, bool prefer_inet6)
 {
     struct sockaddr_storage sa;
     struct addrinfo hints, *res, *ai;
@@ -722,6 +722,10 @@ sock_t sock_get_server_socket (int port, const char *sinterface)
     if (port < 0)
         return SOCK_ERROR;
 
+#ifndef AF_INET6
+    prefer_inet6 = false;
+#endif
+
     memset(&sa,    0, sizeof(sa));
     memset(&hints, 0, sizeof(hints));
 
@@ -733,27 +737,38 @@ sock_t sock_get_server_socket (int port, const char *sinterface)
     if (getaddrinfo(sinterface, service, &hints, &res))
         return SOCK_ERROR;
 
-    for (ai = res; ai; ai = ai->ai_next) {
-        int on = 1;
+    while (true) {
+        for (ai = res; ai; ai = ai->ai_next) {
+            int on = 1;
 
-        sock = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
-        if (sock < 0)
-            continue;
-
-        setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (const void *)&on, sizeof(on));
-
-#ifdef IPV6_V6ONLY
-        on = 0;
-        setsockopt(sock, IPPROTO_IPV6, IPV6_V6ONLY, &on, sizeof(on));
+#ifdef AF_INET6
+            if (prefer_inet6 && ai->ai_family != AF_INET6)
+                continue;
 #endif
 
-        if (bind(sock, ai->ai_addr, ai->ai_addrlen) < 0){
-            sock_close(sock);
-            continue;
+            sock = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
+            if (sock < 0)
+                continue;
+
+            setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (const void *)&on, sizeof(on));
+
+#ifdef IPV6_V6ONLY
+            on = 0;
+            setsockopt(sock, IPPROTO_IPV6, IPV6_V6ONLY, &on, sizeof(on));
+#endif
+
+            if (bind(sock, ai->ai_addr, ai->ai_addrlen) < 0){
+                sock_close(sock);
+                continue;
+            }
+
+            freeaddrinfo(res);
+            return sock;
         }
 
-        freeaddrinfo(res);
-        return sock;
+        if (!prefer_inet6)
+            break;
+        prefer_inet6 = false;
     }
 
     freeaddrinfo(res);
@@ -971,7 +986,7 @@ bool sock_is_ipv4_mapped_supported(void)
     sock_t csock;
     char ip[MAX_ADDR_LEN+1];
 
-    ssock = sock_get_server_socket(0, "::");
+    ssock = sock_get_server_socket(0, "::", true);
 
     if (ssock == SOCK_ERROR)
         return false;
diff --git a/net/sock.h b/net/sock.h
index 0e1b6ac..e2d5be8 100644
--- a/net/sock.h
+++ b/net/sock.h
@@ -153,7 +153,7 @@ int sock_read_bytes(sock_t sock, char *buff, size_t len);
 int sock_read_line(sock_t sock, char *string, const int len);
 
 /* server socket functions */
-sock_t sock_get_server_socket(int port, const char *sinterface);
+sock_t sock_get_server_socket(int port, const char *sinterface, bool prefer_inet6);
 int sock_listen(sock_t serversock, int backlog);
 sock_t sock_accept(sock_t serversock, char *ip, size_t len);