connectx.patch

 configure.ac          | 39 +++++++++++++++++++++++++++++++++++++++
 lib/system/fastopen.c |  4 ++--
 2 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/configure.ac b/configure.ac
index e81ff8970..b25778a83 100644
--- a/configure.ac
+++ b/configure.ac
@@ -127,6 +127,45 @@ case "$host" in
     AC_MSG_CHECKING([whether the linker supports -Wl,-no_weak_imports])
     AC_LINK_IFELSE([AC_LANG_PROGRAM([], [])],
       [AC_MSG_RESULT(yes)], [AC_MSG_RESULT(no); LDFLAGS="$save_LDFLAGS"])
+
+    dnl CURL_CHECK_FUNC_CONNECTX
+    dnl
+    dnl Check if connectx() function is present.
+    dnl The connectx() function call appeared in Darwin 15.0.0
+    dnl but it's not declared using availability attribute.
+    dnl Additionally _connectx symbol is part of OS X 10.9/10.10
+    dnl system lib but does not have specified functionality.
+    dnl
+
+    AC_DEFUN([CURL_CHECK_FUNC_CONNECTX], [
+      AC_REQUIRE([CURL_MAC_CFLAGS])dnl
+      AC_CHECK_FUNCS([connectx])
+      AC_MSG_CHECKING([if connectx is available in deployment target])
+      AC_COMPILE_IFELSE(
+        [AC_LANG_PROGRAM([[
+    #if defined(HAVE_CONNECTX)
+    #  include <Availability.h>
+    #  if defined(__MAC_OS_X_VERSION_MIN_REQUIRED)
+    #    if (__MAC_OS_X_VERSION_MIN_REQUIRED < 101100)
+    #      error Function requires deployment target OS X 10.11 or later
+    #    endif
+    #  elif defined(__IPHONE_OS_VERSION_MIN_REQUIRED)
+    #    if (__IPHONE_OS_VERSION_MIN_REQUIRED < 90000)
+    #      error Function requires deployment target iOS 9.0 or later
+    #    endif
+    #  endif
+    #else
+    #  error Function not present in the headers
+    #endif
+        ]])],
+        [
+          AC_DEFINE(HAVE_VALID_CONNECTX, 1,
+            [Set to 1 if connectx() function have specified functionality.])
+          AC_MSG_RESULT([yes])
+        ],
+        [AC_MSG_RESULT([no])]
+      )
+    ])
   ;;
   *solaris*)
     have_elf=yes
diff --git a/lib/system/fastopen.c b/lib/system/fastopen.c
index 0f673b7c4..2f61b1c28 100644
--- a/lib/system/fastopen.c
+++ b/lib/system/fastopen.c
@@ -126,8 +126,8 @@ tfo_writev(gnutls_transport_ptr_t ptr, const giovec_t * iovec, int iovec_cnt)
 		if (ret == 0)
 			p->connect_only = 0;
 	}
-# elif defined(TCP_FASTOPEN_OSX)
-	{
+# elif defined(TCP_FASTOPEN_OSX) && HAVE_VALID_CONNECTX
+        {
 		sa_endpoints_t endpoints = { .sae_dstaddr = (struct sockaddr*)&p->connect_addr, .sae_dstaddrlen = p->connect_addrlen };
 
 		ret = connectx(fd, &endpoints, SAE_ASSOCID_ANY, CONNECT_RESUME_ON_READ_WRITE | CONNECT_DATA_IDEMPOTENT, NULL, 0, NULL, NULL);