unix: add if_indextoname

if_indextoname(...) is a function defined in <net/if.h>

It is used to convert an IPv6 scope_id into an interface
identifier string such as %eth0 or %lo

The Windows implementation has not been tested.

Adds documentation and an ASSERT to the relevant test case.

PR-URL: libuv#1445

docs/src/misc.rst

@@ -271,6 +271,21 @@ API
     and :man:`inet_pton(3)`. On success they return 0. In case of error
     the target `dst` pointer is unmodified.
 
+.. c:macro:: UV_IF_NAMESIZE
+
+    Maximum IPv6 interface identifier name lenght.  Defined as
+    `IFNAMSIZ` in Unix and `IF_NAMESIZE` in Linux and Windows.
+
+    .. versionadded:: 1.14.0
+
+.. c:function:: char* uv_if_indextoname(unsigned int ifindex, char* ifname)
+
+    Cross-platform IPv6-capable implementation of :man:`if_indextoname(3)`.
+    Writes the result to `ifname`, which must be at least `UV_IF_NAMESIZE` long.
+    On success returns the generated string.  In case of error returns `NULL`.
+
+    .. versionadded:: 1.14.0
+
 .. c:function:: int uv_exepath(char* buffer, size_t* size)
 
     Gets the executable path.

include/uv-unix.h

@@ -32,6 +32,7 @@
 #include <netinet/tcp.h>
 #include <arpa/inet.h>
 #include <netdb.h>
+#include <net/if.h>
 
 #include <termios.h>
 #include <pwd.h>

include/uv.h

@@ -1392,6 +1392,14 @@ UV_EXTERN int uv_ip6_name(const struct sockaddr_in6* src, char* dst, size_t size
 UV_EXTERN int uv_inet_ntop(int af, const void* src, char* dst, size_t size);
 UV_EXTERN int uv_inet_pton(int af, const char* src, void* dst);
 
+#if defined(IF_NAMESIZE)
+# define UV_IF_NAMESIZE IF_NAMESIZE
+#elif defined(IFNAMSIZ)
+# define UV_IF_NAMESIZE IFNAMSIZ
+#endif
+
+UV_EXTERN int uv_if_indextoname(unsigned int ifindex, char* ifname);
+
 UV_EXTERN int uv_exepath(char* buffer, size_t* size);
 
 UV_EXTERN int uv_cwd(char* buffer, size_t* size);

src/uv-common.c

@@ -225,6 +225,35 @@ int uv_ip6_name(const struct sockaddr_in6* src, char* dst, size_t size) {
   return uv_inet_ntop(AF_INET6, &src->sin6_addr, dst, size);
 }
 
+int uv_if_indextoname(unsigned int ifindex, char* ifname) {
+#ifdef _WIN32
+  NET_LUID InterfaceLuid;
+  int error = ConvertInterfaceIndexToLuid(ifindex, &InterfaceLuid);
+  if (NO_ERROR != error) {
+    return -error;
+  }
+  char InterfaceName[NDIS_IF_MAX_STRING_SIZE + 1];
+  int status = ConvertInterfaceLuidToAName(InterfaceLuid, InterfaceName, sizeof(InterfaceName));
+  if (NETIO_ERROR_SUCCESS != status) {
+    return -status;
+  }
+  if (strlen(InterfaceName) >= UV_IF_NAMESIZE) {
+    return UV__ENAMETOOLONG;
+  }
+  strncpy(ifname, InterfaceName, UV_IF_NAMESIZE);
+  return 0;
+#else
+  const int saved_errno = errno;
+  errno = 0;
+  if (NULL == if_indextoname(ifindex, ifname)) {
+    assert(errno);
+    return -errno;
+  }
+  errno = saved_errno;
+  return 0;
+#endif
+}
+
 
 int uv_tcp_bind(uv_tcp_t* handle,
                 const struct sockaddr* addr,

test/test-ip6-addr.c

@@ -67,6 +67,9 @@ TEST_IMPL(ip6_addr_link_local) {
     iface_index = address->address.address6.sin6_scope_id;
     device_name = address->name;
 
+    ASSERT(0 == uv_if_indextoname(iface_index, scoped_addr));
+    ASSERT(0 == strcmp(device_name, scoped_addr));
+
 #ifdef _WIN32
     snprintf(scoped_addr,
              sizeof(scoped_addr),
@@ -96,6 +99,8 @@ TEST_IMPL(ip6_addr_link_local) {
 
   uv_free_interface_addresses(addresses, count);
 
+  ASSERT(0 != uv_if_indextoname((unsigned int)-1, scoped_addr));
+
   MAKE_VALGRIND_HAPPY();
   return 0;
 }