resolve relative item urls with the absolute feed_url

lib/feed_reader/formats/atom.ex

@@ -1,7 +1,7 @@
 defmodule FeedReader.Formats.Atom do
   @moduledoc "Atom feed detection and normalization."
   @behaviour FeedReader.Format
-  alias FeedReader.{Feed, Item, XMLResourceLimits}
+  alias FeedReader.{Feed, Item, URL, XMLResourceLimits}
 
   @impl true
   def matches_prefix?(prefix), do: Regex.match?(~r/<feed\b/is, prefix)
@@ -44,7 +44,13 @@ defmodule FeedReader.Formats.Atom do
     title = raw |> Map.get("title") |> text() |> clean()
     content = raw |> Map.get("content") |> content()
     summary = raw |> Map.get("summary") |> content() || if(is_nil(content), do: title)
-    canonical = raw |> Map.get("link") |> List.wrap() |> find_link() |> correct_url(feed.html_url)
+
+    canonical =
+      raw
+      |> Map.get("link")
+      |> List.wrap()
+      |> find_link()
+      |> URL.resolve_root_relative([feed.html_url, feed.feed_url])
 
     author = get_in(raw, ["author", "name"]) |> text()
 
@@ -88,10 +94,6 @@ defmodule FeedReader.Formats.Atom do
   defp valid_url?(url),
     do: is_binary(url) and url |> URI.parse() |> then(&(!is_nil(&1.scheme) and !is_nil(&1.host)))
 
-  defp correct_url("/" <> _ = url, base) when is_binary(base),
-    do: URI.merge(base, url) |> URI.to_string()
-
-  defp correct_url(url, _base), do: url
   defp clean(nil), do: nil
   defp clean(value), do: value |> HtmlSanitizeEx.strip_tags() |> blank_to_nil()
   defp blank_to_nil(value), do: if(String.trim(value) == "", do: nil, else: String.trim(value))

lib/feed_reader/formats/rdf.ex

@@ -2,7 +2,7 @@ defmodule FeedReader.Formats.RDF do
   @moduledoc "RDF Site Summary format detection and normalization."
   @behaviour FeedReader.Format
 
-  alias FeedReader.{Feed, Item, XMLResourceLimits}
+  alias FeedReader.{Feed, Item, URL, XMLResourceLimits}
 
   @impl true
   def matches_prefix?(prefix), do: Regex.match?(~r/<rdf:rdf\b/is, prefix)
@@ -52,7 +52,12 @@ defmodule FeedReader.Formats.RDF do
     title = raw |> Map.get("title") |> text() |> clean()
     description = text(raw["description"])
     content = text(raw["content:encoded"])
-    canonical = raw |> Map.get("link") |> text() |> correct_url(feed.html_url)
+
+    canonical =
+      raw
+      |> Map.get("link")
+      |> text()
+      |> URL.resolve_root_relative([feed.html_url, feed.feed_url])
 
     {:ok,
      %Item{
@@ -76,11 +81,6 @@ defmodule FeedReader.Formats.RDF do
   defp clean(nil), do: nil
   defp clean(value), do: value |> HtmlSanitizeEx.strip_tags() |> text()
 
-  defp correct_url("/" <> _ = url, base) when is_binary(base),
-    do: URI.merge(base, url) |> URI.to_string()
-
-  defp correct_url(url, _base), do: url
-
   defp published_at(nil), do: DateTime.utc_now(:second)
 
   defp published_at(value) do

lib/feed_reader/formats/rss.ex

@@ -3,7 +3,7 @@ defmodule FeedReader.Formats.RSS do
 
   @behaviour FeedReader.Format
 
-  alias FeedReader.{Feed, Item, XMLResourceLimits}
+  alias FeedReader.{Feed, Item, URL, XMLResourceLimits}
 
   @impl true
   def matches_prefix?(prefix) do
@@ -58,7 +58,7 @@ defmodule FeedReader.Formats.RSS do
     content = value(item, "content:encoded")
     link = value(item, "link")
 
-    canonical_url = correct_url(link, feed.html_url)
+    canonical_url = URL.resolve_root_relative(link, [feed.html_url, feed.feed_url])
     uuid = value(item, "guid") || canonical_url
     summary = description || if(is_nil(content), do: title)
     language_text = Enum.join(Enum.reject([title, content, description], &is_nil/1), "\n")
@@ -91,13 +91,6 @@ defmodule FeedReader.Formats.RSS do
   defp clean_title(nil), do: nil
   defp clean_title(value), do: value |> HtmlSanitizeEx.strip_tags() |> blank_to_nil()
 
-  defp correct_url(nil, _base), do: nil
-
-  defp correct_url("/" <> _ = url, base) when is_binary(base),
-    do: URI.merge(base, url) |> URI.to_string()
-
-  defp correct_url(url, _base), do: url
-
   defp published_at(nil), do: nil
 
   defp published_at(value) do

lib/feed_reader/url.ex

@@ -0,0 +1,32 @@
+defmodule FeedReader.URL do
+  @moduledoc false
+
+  @doc "Resolves root-relative URLs against the first valid absolute base."
+  @spec resolve_root_relative(String.t() | nil, [String.t() | nil]) :: String.t() | nil
+  def resolve_root_relative(nil, _bases), do: nil
+
+  def resolve_root_relative("/" <> _ = url, bases) when is_list(bases) do
+    case Enum.find(bases, &absolute?/1) do
+      nil -> url
+      base -> merge(base, url)
+    end
+  end
+
+  def resolve_root_relative(url, _bases), do: url
+
+  defp absolute?(url) when is_binary(url) do
+    uri = URI.parse(url)
+    is_binary(uri.scheme) and is_binary(uri.host)
+  rescue
+    URI.Error -> false
+  end
+
+  defp absolute?(_url), do: false
+
+  defp merge(base, url) do
+    URI.merge(base, url) |> URI.to_string()
+  rescue
+    URI.Error -> url
+    ArgumentError -> url
+  end
+end

test/feed_reader/atom_test.exs

@@ -20,6 +20,20 @@ defmodule FeedReader.AtomTest do
     assert_receive {:item, %Item{title: "12345", content_summary: "12345"}}
   end
 
+  test "preserves relative links when no absolute feed base is available" do
+    raw = %{"title" => "Story", "link" => [%{"href" => "/story", "rel" => "alternate"}]}
+
+    assert {:ok, %Item{canonical_url: "/story"}} =
+             Atom.normalize_item(raw, %Feed{html_url: "/"}, [])
+
+    assert {:ok, %Item{canonical_url: "https://example.com/story"}} =
+             Atom.normalize_item(
+               raw,
+               %Feed{html_url: "/", feed_url: "https://example.com/feed.xml"},
+               []
+             )
+  end
+
   test "accounts for parser failures and closes empty feeds" do
     handler = Atom.handler()
     sink = fn event -> send(self(), event) end

test/feed_reader/rdf_test.exs

@@ -34,6 +34,20 @@ defmodule FeedReader.RDFTest do
     assert_receive {:item, %Item{title: "Title only", content_full: nil, content_summary: nil}}
   end
 
+  test "preserves relative links when no absolute feed base is available" do
+    raw = %{"title" => "Story", "link" => "/story"}
+
+    assert {:ok, %Item{canonical_url: "/story"}} =
+             RDF.normalize_item(raw, %Feed{html_url: "/"}, [])
+
+    assert {:ok, %Item{canonical_url: "https://example.com/story"}} =
+             RDF.normalize_item(
+               raw,
+               %Feed{html_url: "/", feed_url: "https://example.com/feed.xml"},
+               []
+             )
+  end
+
   test "enforces shared SAX limits and reports malformed XML" do
     sink = fn _event -> :ok end
 

test/feed_reader/rss_test.exs

@@ -1,7 +1,7 @@
 defmodule FeedReader.RSSTest do
   use ExUnit.Case, async: true
 
-  alias FeedReader.Formats.RSS
+  alias FeedReader.{Feed, Formats.RSS, Item}
 
   @xml ~s(<rss version="2.0"><channel><title>Example</title><description>Latest news</description><link>https://example.com/</link><category>News</category><category>News</category><item><title>Story</title><guid isPermaLink="false">story-1</guid><link>/story</link><author>Writer</author><description>Summary</description><content:encoded><![CDATA[<p>Full text</p>]]></content:encoded><pubDate>Mon, 24 Feb 2025 17:00:05 GMT</pubDate></item><item><title> </title><link>https://example.com/second</link><pubDate>not a date</pubDate></item><item><title> </title></item></channel></rss>)
 
@@ -13,6 +13,22 @@ defmodule FeedReader.RSSTest do
     assert {:ok, _} = parse("<rss version='2.0'><channel/></rss>", sink)
   end
 
+  test "preserves relative links when no absolute feed base is available" do
+    assert {:ok, %Item{canonical_url: "/story"}} =
+             RSS.normalize_item(
+               %{"title" => "Story", "link" => "/story"},
+               %Feed{html_url: "/"},
+               []
+             )
+
+    assert {:ok, %Item{canonical_url: "https://example.com/story"}} =
+             RSS.normalize_item(
+               %{"title" => "Story", "link" => "/story"},
+               %Feed{html_url: "/", feed_url: "https://example.com/feed.xml"},
+               []
+             )
+  end
+
   test "stops malformed and over-budget input and rejects orphan SAX events" do
     sink = fn _event -> :ok end
     assert {:error, _} = parse("<rss version='2.0'>", sink)