Updte DNS module and DNSResolver behaviour

Author: martosaur

Diff for: guides/migrating_to_1.0.md

@@ -28,3 +28,15 @@ iex> Application.put_env(:safeurl, :detailed_error, false)
 iex> SafeURL.validate("http://localhost")
 {:error, :restricted}
 ```
+
+### Change modules implementing `SafeURL.DNSResolver` behaviour
+
+If you have a module that implements `SafeURL.DNSResolver` behaviour, note that
+`DNSResolver.resolve/1` signature has changed. Specifically, the ok tuple should now
+always return a list of IPs. A single IP is not a valid return type:
+
+```elixir
+# DNS is the default implementation
+iex> DNS.resolve("wikipedia.org")
+{:ok, [{198, 35, 26, 96}]}
+```

Diff for: lib/safeurl/dns_resolver.ex

@@ -69,6 +69,5 @@ defmodule SafeURL.DNSResolver do
 
   """
 
-  @type resolution :: :inet.ip() | [:inet.ip()]
-  @callback resolve(host :: binary()) :: {:ok, resolution()} | {:error, atom()}
+  @callback resolve(host :: String.t()) :: {:ok, list()} | {:error, :inet_res.res_error()}
 end

Diff for: lib/safeurl/safeurl.ex

@@ -239,7 +239,7 @@ defmodule SafeURL do
       {:error, :einval} ->
         # TODO: safely handle multiple IPs/round-robin DNS
         case dns_module.resolve(hostname) do
-          {:ok, ips} -> ips |> List.wrap() |> List.first()
+          {:ok, [ip | _]} -> ip
           {:error, _reason} -> nil
         end
     end

Diff for: mix.exs

@@ -54,7 +54,7 @@ defmodule SafeURL.MixProject do
     [
       {:httpoison, "~> 1.0 or ~> 2.0", optional: true},
       {:inet_cidr, "~> 1.0 and >= 1.0.6"},
-      {:dns, "~> 2.2"},
+      {:dns, "~> 2.4"},
       {:tesla, "~> 1.0", optional: true},
       {:ex_doc, ">= 0.0.0", only: :dev, runtime: false}
     ]