threadedresolver: Return valid addresses when only having loopback interfaces

The AI_ADDRCONFIG flag filters out addresses for invalid interfaces. This causes it to resolve nothing when only having loopback interfaces.

So we can detect if you only have loopback interfaces, request all addresses, and filter out non-loopback results.

Closes #3641

gio/gthreadedresolver.c

@@ -40,6 +40,10 @@
 #include "gsocketaddress.h"
 #include "gsrvtarget.h"
 
+#if HAVE_GETIFADDRS
+#include <ifaddrs.h>
+#endif
+
 /*
  * GThreadedResolver is a threaded wrapper around the system libc’s
  * `getaddrinfo()`.
@@ -255,6 +259,53 @@ lookup_data_free (LookupData *data)
   g_free (data);
 }
 
+static gboolean
+only_has_loopback_interfaces (void)
+{
+#if HAVE_GETIFADDRS
+  struct ifaddrs *addrs;
+  gboolean only_loopback = TRUE;
+
+  if (getifaddrs (&addrs) != 0)
+    {
+      int saved_errno = errno;
+      g_debug ("getifaddrs() failed: %s", g_strerror (saved_errno));
+      return FALSE;
+    }
+
+  for (struct ifaddrs *addr = addrs; addr; addr = addr->ifa_next)
+    {
+      struct sockaddr *sa = addr->ifa_addr;
+      GSocketAddress *saddr = g_socket_address_new_from_native (sa, sizeof (struct sockaddr));
+
+      if (!saddr)
+        continue;
+
+      if (!G_IS_INET_SOCKET_ADDRESS (saddr))
+        {
+          g_object_unref (saddr);
+          continue;
+        }
+
+      GInetAddress *inetaddr = g_inet_socket_address_get_address (G_INET_SOCKET_ADDRESS (saddr));
+      if (!g_inet_address_get_is_loopback (inetaddr))
+        {
+          only_loopback = FALSE;
+          g_object_unref (saddr);
+          break;
+        }
+
+      g_object_unref (saddr);
+    }
+
+  freeifaddrs (addrs);
+  return only_loopback;
+#else /* FIXME: Check GetAdaptersAddresses() on win32. */
+  return FALSE;
+#endif
+}
+
+
 static GList *
 do_lookup_by_name (const gchar   *hostname,
                    int            address_family,
@@ -266,8 +317,14 @@ do_lookup_by_name (const gchar   *hostname,
   gint retval;
   struct addrinfo addrinfo_hints = { 0 };
 
+  /* In general we only want IPs for valid interfaces.
+   * However this will return nothing if you only have loopback interfaces.
+   * Instead in this case we will manually filter out invalid IPs. */
+  gboolean only_loopback = only_has_loopback_interfaces ();
+
 #ifdef AI_ADDRCONFIG
-  addrinfo_hints.ai_flags = AI_ADDRCONFIG;
+  if (!only_loopback)
+    addrinfo_hints.ai_flags = AI_ADDRCONFIG;
 #endif
   /* socktype and protocol don't actually matter, they just get copied into the
   * returned addrinfo structures (and then we ignore them). But if
@@ -295,8 +352,14 @@ do_lookup_by_name (const gchar   *hostname,
               continue;
             }
 
-          addr = g_object_ref (g_inet_socket_address_get_address ((GInetSocketAddress *)sockaddr));
-          addresses = g_list_prepend (addresses, addr);
+          addr = g_inet_socket_address_get_address ((GInetSocketAddress *) sockaddr);
+          if (only_loopback && !g_inet_address_get_is_loopback (addr))
+            {
+              g_object_unref (sockaddr);
+              continue;
+            }
+
+          addresses = g_list_prepend (addresses, g_object_ref (addr));
           g_object_unref (sockaddr);
         }
 

meson.build

@@ -715,6 +715,7 @@ functions = [
   'getfsent',
   'getfsstat',
   'getgrgid_r',
+  'getifaddrs',
   'getmntent_r',
   'getpwuid_r',
   'getresuid',