Use URI.parse to handle url edge cases

CHANGELOG.md

@@ -4,6 +4,8 @@
 
 Requires Elixir 1.13+
 
+- Fixed bug with trailing slash in `:base_url` not being ommitted when concatenating with relative path
+
 ## v0.2.9 (2023-11-22)
 
 - Fixed bug where `Req` was not used by default if included in project

lib/assent/strategy.ex

@@ -183,11 +183,14 @@ defmodule Assent.Strategy do
 
   defp encode_value(value), do: URI.encode_www_form(Kernel.to_string(value))
 
-  defp endpoint(base_url, <<"/"::utf8, _::binary>> = uri),
-    do: base_url <> uri
+  defp endpoint(base_url, "/" <> uri = all) do
+    case :binary.last(base_url) do
+      ?/ -> base_url <> uri
+      _ -> base_url <> all
+    end
+  end
 
-  defp endpoint(_base_url, url),
-    do: url
+  defp endpoint(_base_url, uri), do: uri
 
   @doc """
   Normalize API user request response into standard claims

test/assent/strategy_test.exs

@@ -248,8 +248,20 @@ defmodule Assent.StrategyTest do
   end
 
   test "to_url/3" do
-    assert Strategy.to_url("http://localhost", "/path", a: 1, b: [c: 2, d: [e: 3]], f: [4, 5]) ==
-             "http://localhost/path?a=1&b[c]=2&b[d][e]=3&f[]=4&f[]=5"
+    assert Strategy.to_url("http://example.com", "/path") == "http://example.com/path"
+    assert Strategy.to_url("http://example.com/", "/path") == "http://example.com/path"
+
+    assert Strategy.to_url("http://example.com/path", "/other-path") ==
+             "http://example.com/path/other-path"
+
+    assert Strategy.to_url("http://example.com/path/", "/other-path") ==
+             "http://example.com/path/other-path"
+
+    assert Strategy.to_url("http://example.com/path", "http://example.org/other-path") ==
+             "http://example.org/other-path"
+
+    assert Strategy.to_url("http://example.com", "/path", a: 1, b: [c: 2, d: [e: 3]], f: [4, 5]) ==
+             "http://example.com/path?a=1&b[c]=2&b[d][e]=3&f[]=4&f[]=5"
   end
 
   test "normalize_userinfo/2" do