Allow override of public ip, open for someone else (#11)

* Allow override of public ip, open for someone else

    Sparoid.auth(.., open_for_ip:)

Useful when Sparoid.auth operation isn't done on the instance that will
connect, e.g. web server letting a browser accessing a host.

Performance detail, passing an `Resolv::IPv4` object to `Resolv::IPv4.create`
will just trigger early return, so it's fast.

lib/sparoid.rb

@@ -12,10 +12,10 @@ module Sparoid # rubocop:disable Metrics/ModuleLength
   SPAROID_CACHE_PATH = ENV.fetch("SPAROID_CACHE_PATH", "/tmp/.sparoid_public_ip")
 
   # Send an authorization packet
-  def auth(key, hmac_key, host, port)
+  def auth(key, hmac_key, host, port, open_for_ip: cached_public_ip)
     addrs = resolve_ip_addresses(host, port)
-
-    msg = message(cached_public_ip)
+    ip = Resolv::IPv4.create(open_for_ip)
+    msg = message(ip)
     data = prefix_hmac(hmac_key, encrypt(key, msg))
     sendmsg(addrs, data)
 

test/sparoid_test.rb

@@ -39,6 +39,19 @@ def test_it_sends_message
     end
   end
 
+  def test_it_opens_for_passed_in_ip_argument
+    key = "0000000000000000000000000000000000000000000000000000000000000000"
+    hmac_key = "0000000000000000000000000000000000000000000000000000000000000000"
+    UDPSocket.open do |server|
+      server.bind("127.0.0.1", 0)
+      port = server.addr[1]
+      s = Sparoid::Instance.new
+      s.stub(:public_ip, ->(*_) { raise "public_ip method not expected to be called" }) do
+        s.auth(key, hmac_key, "127.0.0.1", port, open_for_ip: "127.0.1.1")
+      end
+    end
+  end
+
   def test_it_sends_message_with_empty_cache_file
     Sparoid.stub_const(:SPAROID_CACHE_PATH, Tempfile.new.path) do
       assert_output(nil, "") { test_it_sends_message }