From 1e87d9252782423885f569a789714966c237b61f Mon Sep 17 00:00:00 2001
From: Luca Boccassi <luca.boccassi@gmail.com>
Date: Thu, 7 Apr 2016 13:15:41 +0100
Subject: [PATCH] Problem: zmq_connect (TCP) has no IPv4 fallback

Solution: if opening an IPv6 TCP socket fails because IPv6 is not
available, try to open an IPv4 socket instead when creating and
connecting a TCP endpoint.
---
 src/tcp_connecter.cpp | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/src/tcp_connecter.cpp b/src/tcp_connecter.cpp
index fdbc45c2..75c049e9 100644
--- a/src/tcp_connecter.cpp
+++ b/src/tcp_connecter.cpp
@@ -235,6 +235,21 @@ int zmq::tcp_connecter_t::open ()
 
     //  Create the socket.
     s = open_socket (tcp_addr->family (), SOCK_STREAM, IPPROTO_TCP);
+
+    //  IPv6 address family not supported, try automatic downgrade to IPv4.
+    if (s == -1 && tcp_addr->family () == AF_INET6
+    && errno == EAFNOSUPPORT
+    && options.ipv6) {
+        rc = addr->resolved.tcp_addr->resolve (
+            addr->address.c_str (), false, false);
+        if (rc != 0) {
+            delete addr->resolved.tcp_addr;
+            addr->resolved.tcp_addr = NULL;
+            return -1;
+        }
+        s = open_socket (AF_INET, SOCK_STREAM, IPPROTO_TCP);
+    }
+
 #ifdef ZMQ_HAVE_WINDOWS
     if (s == INVALID_SOCKET) {
         errno = wsa_error_to_errno (WSAGetLastError ());