tcp_connect forces errno to EINVAL if it can solve DNS address.

src/lua/bsdsocket.lua

@@ -966,6 +966,11 @@ local function tcp_connect(host, port, timeout)
     if dns == nil then
         return nil
     end
+
+    if #dns == 0 then
+        box.errno(box.errno.EINVAL)
+        return nil
+    end
     for i, remote in pairs(dns) do
         timeout = stop - box.time()
         if timeout <= 0 then

test/box/bsdsocket.result

@@ -1183,3 +1183,7 @@ lua s:close()
 ---
  - true
 ...
+lua box.cjson.encode{ box.socket.tcp_connect('test:test@localhost:3303') == nil, box.errno.strerror() }
+---
+ - [true,"Invalid argument"]
+...

test/box/bsdsocket.test

@@ -385,3 +385,6 @@ exec admin "lua s ~= nil"
 exec admin "lua s:close()"
 if os.path.exists(path):
     print 'unix socket was not removed: test failed'
+
+
+exec admin "lua box.cjson.encode{ box.socket.tcp_connect('test:test@localhost:3303') == nil, box.errno.strerror() }"