Bring this back.

src/core/io/srt_io.ml

@@ -74,12 +74,7 @@ let getaddrinfo ~(log : Log.t) ~prefer_address address port =
   let open Posix_socket in
   let hints = allocate_n Addrinfo.t ~count:1 in
   hints |-> Addrinfo.ai_flags <-@ ni_numerichost;
-  (hints |-> Addrinfo.ai_family
-  <-@
-  match prefer_address with
-    | `System_default -> af_unspec
-    | `Ipv4 -> af_inet
-    | `Ipv6 -> af_inet6);
+  hints |-> Addrinfo.ai_family <-@ af_unspec;
   hints |-> Addrinfo.ai_socktype <-@ sock_stream;
   match getaddrinfo ~hints ~port:(`Int port) address with
     | ptr when is_null !@ptr ->
@@ -89,7 +84,31 @@ let getaddrinfo ~(log : Log.t) ~prefer_address address port =
                address port)
           "srt"
     | ptr ->
-        let sockaddr = !@ptr in
+        let first_address = !@ptr in
+        let sockaddr =
+          match prefer_address with
+            | `System_default -> first_address
+            | `Ipv4 ->
+                let rec f ptr cur =
+                  let sockaddr = !@ptr in
+                  if is_null sockaddr then cur
+                  else (
+                    match !@(sockaddr |-> Sockaddr.sa_family) with
+                      | id when id = af_inet -> sockaddr
+                      | _ -> f (ptr +@ 1) cur)
+                in
+                f ptr first_address
+            | `Ipv6 ->
+                let rec f ptr cur =
+                  let sockaddr = !@ptr in
+                  if is_null sockaddr then cur
+                  else (
+                    match !@(sockaddr |-> Sockaddr.sa_family) with
+                      | id when id = af_inet6 -> sockaddr
+                      | _ -> f (ptr +@ 1) cur)
+                in
+                f ptr first_address
+        in
         if log#active 5 then
           log#f 5 "Address %s:%n resolved to: %s" address port
             (string_of_address (to_unix_sockaddr sockaddr));