Add Webmention endpoint discovery

config/config.exs

@@ -40,6 +40,8 @@ config :clacks, Oban,
   prune: {:maxlen, 10_000},
   queues: [federate: 10]
 
+config :floki, :html_parser, Floki.HTMLParser.FastHtml
+
 # Import environment specific config. This must remain at the bottom
 # of this file so it overrides the configuration defined above.
 import_config "#{Mix.env()}.exs"

lib/clacks/http.ex

@@ -27,15 +27,7 @@ defmodule Clacks.HTTP do
         |> Enum.find(fn {name, _value} -> String.downcase(name) == "location" end)
         |> case do
           {_, new_url} ->
-            new_url =
-              case URI.parse(new_url) do
-                %URI{host: nil, path: path} ->
-                  # relative path
-                  %URI{URI.parse(url) | path: path} |> URI.to_string()
-
-                uri ->
-                  uri
-              end
+            new_url = URI.merge(URI.parse(url), URI.parse(new_url))
 
             Logger.debug("Got 301 redirect from #{url} to #{new_url}")
             fetch(method, new_url, headers)

lib/clacks/webmention/endpoint.ex

@@ -0,0 +1,119 @@
+defmodule Clacks.Webmention.Endpoint do
+  require Logger
+
+  @spec find_endpoint(url :: String.t()) :: URI.t() | nil
+  def find_endpoint(url) do
+    case find_endpoint_by_header(url) do
+      nil ->
+        find_endpoint_by_html(url)
+
+      :error ->
+        :error
+
+      endpoint ->
+        endpoint
+    end
+  end
+
+  defp find_endpoint_by_header(url) do
+    case Clacks.HTTP.head(url) do
+      {:ok, %HTTPoison.Response{headers: headers, request: %HTTPoison.Request{url: final_url}}} ->
+        headers
+        |> Enum.filter(fn {name, _} -> String.downcase(name) == "link" end)
+        |> webmention_link()
+        |> case do
+          nil ->
+            nil
+
+          str when is_binary(str) ->
+            URI.merge(final_url, str)
+        end
+
+      {:error, reason} ->
+        Logger.warn("Unable to find Webmention endpoint for '#{url}': #{reason}")
+        :error
+    end
+  end
+
+  defp webmention_link([]), do: nil
+
+  defp webmention_link([{_, value} | rest]) do
+    String.split(value, ",")
+    |> Enum.map(&parse_link_header/1)
+    |> Enum.find(fn {rels, _} -> "webmention" in rels end)
+    |> case do
+      nil ->
+        webmention_link(rest)
+
+      {_, res} ->
+        res
+    end
+  end
+
+  defp parse_link_header(value) do
+    [value | params] = String.split(value, ";")
+
+    uri_reference =
+      value
+      |> String.trim()
+      |> String.slice(1..-1)
+
+    {_, rel} =
+      params
+      |> Enum.map(fn str ->
+        str = String.trim(str)
+        [name | rest] = String.split(str, "=")
+        rest = Enum.join(rest, "=")
+
+        value =
+          if String.starts_with?(rest, "\"") do
+            {_, rest} = String.split_at(rest, 1)
+
+            if String.ends_with?(rest, "\"") do
+              {rest, _} = String.split_at(rest, -1)
+              rest
+            else
+              rest
+            end
+          else
+            rest
+          end
+
+        {name, value}
+      end)
+      |> Enum.find(fn {name, _} -> String.downcase(name) == "rel" end)
+
+    rels = String.split(rel, ~r/\s+/) |> Enum.map(&String.downcase/1)
+
+    {rels, uri_reference}
+  end
+
+  defp find_endpoint_by_html(url) do
+    case Clacks.HTTP.get(url) do
+      {:ok, %HTTPoison.Response{body: body, request: %HTTPoison.Request{url: final_url}}} ->
+        {:ok, doc} = Floki.parse_document(body)
+
+        Floki.find(doc, "link[rel~=webmention], a[rel~=webmention]")
+        |> Enum.reduce_while(nil, fn el, _acc ->
+          case Floki.attribute(el, "href") do
+            [href] when is_binary(href) ->
+              {:halt, href}
+
+            _ ->
+              {:cont, nil}
+          end
+        end)
+        |> case do
+          nil ->
+            nil
+
+          str when is_binary(str) ->
+            URI.merge(final_url, str)
+        end
+
+      {:error, reason} ->
+        Logger.warn("Unable to find Webmention endpoint for '#{url}': #{reason}")
+        :error
+    end
+  end
+end

mix.exs

@@ -52,7 +52,9 @@ defmodule Clacks.MixProject do
       {:bcrypt_elixir, "~> 2.0"},
       {:oban, "~> 1.2.0"},
       {:fast_sanitize, "~> 0.1.7"},
-      {:dialyxir, "~> 1.0", only: [:dev], runtime: false}
+      {:fast_html, "~> 1.0.3"},
+      {:dialyxir, "~> 1.0", only: [:dev], runtime: false},
+      {:floki, "~> 0.26.0"}
     ]
   end
 

mix.lock

@@ -19,8 +19,10 @@
   "fast_sanitize": {:hex, :fast_sanitize, "0.1.7", "2a7cd8734c88a2de6de55022104f8a3b87f1fdbe8bbf131d9049764b53d50d0d", [:mix], [{:fast_html, "~> 1.0", [hex: :fast_html, repo: "hexpm", optional: false]}, {:plug, "~> 1.8", [hex: :plug, repo: "hexpm", optional: false]}], "hexpm", "f39fe8ea08fbac17487c30bf09b7d9f3e12472e51fb07a88ffeb8fd17da8ab67"},
   "file_system": {:hex, :file_system, "0.2.7", "e6f7f155970975789f26e77b8b8d8ab084c59844d8ecfaf58cbda31c494d14aa", [:mix], [], "hexpm", "b4cfa2d69c7f0b18fd06db222b2398abeef743a72504e6bd7df9c52f171b047f"},
   "flake_id": {:hex, :flake_id, "0.1.0", "7716b086d2e405d09b647121a166498a0d93d1a623bead243e1f74216079ccb3", [:mix], [{:base62, "~> 1.2", [hex: :base62, repo: "hexpm", optional: false]}, {:ecto, ">= 2.0.0", [hex: :ecto, repo: "hexpm", optional: true]}], "hexpm", "31fc8090fde1acd267c07c36ea7365b8604055f897d3a53dd967658c691bd827"},
+  "floki": {:hex, :floki, "0.26.0", "4df88977e2e357c6720e1b650f613444bfb48c5acfc6a0c646ab007d08ad13bf", [:mix], [{:html_entities, "~> 0.5.0", [hex: :html_entities, repo: "hexpm", optional: false]}], "hexpm", "e7b66ce7feef5518a9cd9fc7b52dd62a64028bd9cb6d6ad282a0f0fc90a4ae52"},
   "gettext": {:hex, :gettext, "0.17.0", "abe21542c831887a2b16f4c94556db9c421ab301aee417b7c4fbde7fbdbe01ec", [:mix], [], "hexpm", "e0b8598e802676c81e66b061a2148c37c03886b24a3ca86a1f98ed40693b94b3"},
   "hackney": {:hex, :hackney, "1.15.2", "07e33c794f8f8964ee86cebec1a8ed88db5070e52e904b8f12209773c1036085", [:rebar3], [{:certifi, "2.5.1", [hex: :certifi, repo: "hexpm", optional: false]}, {:idna, "6.0.0", [hex: :idna, repo: "hexpm", optional: false]}, {:metrics, "1.0.1", [hex: :metrics, repo: "hexpm", optional: false]}, {:mimerl, "~>1.1", [hex: :mimerl, repo: "hexpm", optional: false]}, {:ssl_verify_fun, "1.1.5", [hex: :ssl_verify_fun, repo: "hexpm", optional: false]}], "hexpm", "e0100f8ef7d1124222c11ad362c857d3df7cb5f4204054f9f0f4a728666591fc"},
+  "html_entities": {:hex, :html_entities, "0.5.1", "1c9715058b42c35a2ab65edc5b36d0ea66dd083767bef6e3edb57870ef556549", [:mix], [], "hexpm", "30efab070904eb897ff05cd52fa61c1025d7f8ef3a9ca250bc4e6513d16c32de"},
   "http_signatures": {:git, "https://git.pleroma.social/pleroma/http_signatures.git", "293d77bb6f4a67ac8bde1428735c3b42f22cbb30", [ref: "293d77bb6f4a67ac8bde1428735c3b42f22cbb30"]},
   "httpoison": {:hex, :httpoison, "1.5.1", "0f55b5b673b03c5c327dac7015a67cb571b99b631acc0bc1b0b98dcd6b9f2104", [:mix], [{:hackney, "~> 1.8", [hex: :hackney, repo: "hexpm", optional: false]}], "hexpm", "191a3b6329c917de4e7ca68431919a59bf19e60694b313a69bc1f56a4cb160bf"},
   "idna": {:hex, :idna, "6.0.0", "689c46cbcdf3524c44d5f3dde8001f364cd7608a99556d8fbd8239a5798d4c10", [:rebar3], [{:unicode_util_compat, "0.4.1", [hex: :unicode_util_compat, repo: "hexpm", optional: false]}], "hexpm", "4bdd305eb64e18b0273864920695cb18d7a2021f31a11b9c5fbcd9a253f936e2"},