738 		-- Check hostname validity

   739 		do

   740 			local idna = require "prosody.util.encodings".idna;

   741 			local invalid_hosts = {};

   742 			local alabel_hosts = {};

   743 			for host in it.filter("*", pairs(configmanager.getconfig())) do

   744 				local _, h, _ = jid_split(host);

   745 				if not h or not idna.to_ascii(h) then

   746 					table.insert(invalid_hosts, host);

   747 				else

   748 					for label in h:gmatch("[^%.]+") do

   749 						if label:match("^xn%-%-") then

   750 							table.insert(alabel_hosts, host);

   751 							break;

   752 						end

   753 					end

   754 				end

   755 			end

   756 

   757 			if #invalid_hosts > 0 then

   758 				table.sort(invalid_hosts);

   759 				print("");

   760 				print("    Your configuration contains invalid host names:");

   761 				print("        "..table.concat(invalid_hosts, "\n        "));

   762 				print("");

   763 				print("    Clients may not be able to log in to these hosts, or you may not be able to");

   764 				print("    communicate with remote servers.");

   765 				print("    Use a valid domain name to correct this issue.");

   766 			end

   767 

   768 			if #alabel_hosts > 0 then

   769 				table.sort(alabel_hosts);

   770 				print("");

   771 				print("    Your configuration contains incorrectly-encoded hostnames:");

   772 				for _, ahost in ipairs(alabel_hosts) do

   773 					print(("        '%s' (should be '%s')"):format(ahost, idna.to_unicode(ahost)));

   774 				end

   775 				print("");

   776 				print("    Clients may not be able to log in to these hosts, or you may not be able to");

   777 				print("    communicate with remote servers.");

   778 				print("    To correct this issue, use the Unicode version of the domain in Prosody's config file.");

   779 			end

   780 

   781 			if #invalid_hosts > 0 or #alabel_hosts > 0 then

   782 				print("");

   783 				print("WARNING: Changing the name of a VirtualHost in Prosody's config file");

   784 				print("         WILL NOT migrate any existing data (user accounts, etc.) to the new name.");

   785 				ok = false;

   786 			end

   787 		end

   788