util.prosodyctl.check: Fix error where hostname can't be turned into A label

Where gethostname or tohostname returns an invalid name, e.g. containing
underscores or something, to_ascii would reject this and return nil,
which triggers an error in the dns lookup.

Reported by prova2 in the chat, for whom tohostname returned a long name
containing underscores.

1 files changed, 5 insertions, 4 deletions

diff --git a/util/prosodyctl/check.lua b/util/prosodyctl/check.lua
index 2fd3c784..2e3fb6d8 100644
--- a/util/prosodyctl/check.lua
+++ b/util/prosodyctl/check.lua
@@ -751,16 +751,17 @@ local function check(arg)
 
 		local fqdn = socket.dns.tohostname(socket.dns.gethostname());
 		if fqdn then
-			do
-				local res = dns.lookup(idna.to_ascii(fqdn), "A");
+			local fqdn_a = idna.to_ascii(fqdn);
+			if fqdn_a then
+				local res = dns.lookup(fqdn_a, "A");
 				if res then
 					for _, record in ipairs(res) do
 						external_addresses:add(record.a);
 					end
 				end
 			end
-			do
-				local res = dns.lookup(idna.to_ascii(fqdn), "AAAA");
+			if fqdn_a then
+				local res = dns.lookup(fqdn_a, "AAAA");
 				if res then
 					for _, record in ipairs(res) do
 						external_addresses:add(record.aaaa);