fix S3 links encoding in Mediaproxy

lib/pleroma/web/media_proxy/media_proxy.ex

@@ -19,11 +19,16 @@ def url(url) do
     else
       secret = Application.get_env(:pleroma, Pleroma.Web.Endpoint)[:secret_key_base]
 
+      # Must preserve `%2F` for compatibility with S3 (https://git.pleroma.social/pleroma/pleroma/issues/580)
+      replacement = get_replacement(url, ":2F:")
+
       # The URL is url-decoded and encoded again to ensure it is correctly encoded and not twice.
       base64 =
         url
+        |> String.replace("%2F", replacement)
         |> URI.decode()
         |> URI.encode()
+        |> String.replace(replacement, "%2F")
         |> Base.url_encode64(@base64_opts)
 
       sig = :crypto.hmac(:sha, secret, base64)
@@ -60,4 +65,12 @@ def build_url(sig_base64, url_base64, filename \\ nil) do
     |> Enum.filter(fn value -> value end)
     |> Path.join()
   end
+
+  defp get_replacement(url, replacement) do
+    if String.contains?(url, replacement) do
+      get_replacement(url, replacement <> replacement)
+    else
+      replacement
+    end
+  end
 end

test/media_proxy_test.exs

@@ -140,6 +140,15 @@ test "uses the configured base_url" do
 
       assert String.starts_with?(encoded, Pleroma.Config.get([:media_proxy, :base_url]))
     end
+
+    # https://git.pleroma.social/pleroma/pleroma/issues/580
+    test "encoding S3 links (must preserve `%2F`)" do
+      url =
+        "https://s3.amazonaws.com/example/test.png?X-Amz-Credential=your-access-key-id%2F20130721%2Fus-east-1%2Fs3%2Faws4_request"
+
+      encoded = url(url)
+      assert decode_result(encoded) == url
+    end
   end
 
   describe "when disabled" do