Implement basic WebFinger endpoint

As prep for ActivityPub!

lib/asciinema_web.ex

@@ -177,6 +177,13 @@ defmodule AsciinemaWeb do
     end
   end
 
+  def json do
+    quote do
+      # Routes generation with the ~p sigil
+      unquote(verified_routes())
+    end
+  end
+
   def verified_routes do
     quote do
       use Phoenix.VerifiedRoutes,

lib/asciinema_web/controllers/webfinger_controller.ex

@@ -0,0 +1,20 @@
+defmodule AsciinemaWeb.WebFingerController do
+  use AsciinemaWeb, :new_controller
+  alias Asciinema.Accounts
+
+  def show(conn, %{"resource" => resource}) do
+    resource =
+      resource
+      |> String.trim()
+      |> String.downcase()
+
+    with "acct:" <> acct <- resource,
+         [username, domain] <- String.split(acct, "@"),
+         ^domain <- AsciinemaWeb.Endpoint.host(),
+         {:username, user} when not is_nil(user) <- Accounts.lookup_user(username) do
+      render(conn, :show, user: user, domain: domain)
+    else
+      _ -> {:error, :not_found}
+    end
+  end
+end

lib/asciinema_web/controllers/webfinger_json.ex

@@ -0,0 +1,19 @@
+defmodule AsciinemaWeb.WebFingerJSON do
+  use AsciinemaWeb, :json
+
+  def show(%{user: %{username: username}, domain: domain}) do
+    %{
+      subject: "acct:#{username}@#{domain}",
+      aliases: [
+        url(~p"/~#{username}")
+      ],
+      links: [
+        %{
+          rel: "http://webfinger.net/rel/profile-page",
+          type: "text/html",
+          href: url(~p"/~#{username}")
+        }
+      ]
+    }
+  end
+end

lib/asciinema_web/router.ex

@@ -42,6 +42,10 @@ defmodule AsciinemaWeb.Router do
     plug :put_secure_browser_headers
   end
 
+  pipeline :webfinger do
+    plug :put_format, :json
+  end
+
   scope "/", AsciinemaWeb do
     pipe_through :asciicast
 
@@ -54,6 +58,11 @@ defmodule AsciinemaWeb.Router do
     get "/oembed", OembedController, :show
   end
 
+  scope "/", AsciinemaWeb do
+    pipe_through :webfinger
+    get "/.well-known/webfinger", WebFingerController, :show
+  end
+
   scope "/", AsciinemaWeb do
     # Use the default browser stack
     pipe_through :browser

test/controllers/webfinger_controller_test.exs

@@ -0,0 +1,48 @@
+defmodule Asciinema.WebFingerControllerTest do
+  use AsciinemaWeb.ConnCase
+  import Asciinema.Factory
+
+  setup [:create_user]
+
+  describe "show" do
+    test "returns basic info", %{conn: conn} do
+      conn = get(conn, ~p"/.well-known/webfinger?resource=acct:Pinky@localhost")
+
+      assert json_response(conn, 200) == %{
+               "subject" => "acct:Pinky@localhost",
+               "aliases" => [
+                 url(~p"/~Pinky")
+               ],
+               "links" => [
+                 %{
+                   "rel" => "http://webfinger.net/rel/profile-page",
+                   "type" => "text/html",
+                   "href" => url(~p"/~Pinky")
+                 }
+               ]
+             }
+    end
+
+    test "does case-insensitive acct lookup", %{conn: conn} do
+      conn = get(conn, ~p"/.well-known/webfinger?resource=acct:pinky@lOcaLhOst")
+
+      assert %{"subject" => "acct:Pinky@localhost"} = json_response(conn, 200)
+    end
+
+    test "returns 404 when username not found", %{conn: conn} do
+      conn = get(conn, ~p"/.well-known/webfinger?resource=acct:nope@localhost")
+
+      assert json_response(conn, 404)
+    end
+
+    test "returns 404 when domain doesn't match", %{conn: conn} do
+      conn = get(conn, ~p"/.well-known/webfinger?resource=acct:[email protected]")
+
+      assert json_response(conn, 404)
+    end
+  end
+
+  defp create_user(_) do
+    %{user: insert(:user, username: "Pinky")}
+  end
+end