Use MDEx streaming to render chat content

docs/architecture.md

@@ -296,7 +296,7 @@ All authenticated routes live inside a single `live_session` with three `on_moun
 | Module | Purpose |
 |--------|---------|
 | `ErrorMessages` | Maps internal error terms (atoms, structs) to user-friendly gettext strings via `friendly_message/1` |
-| `Markdown` | Markdown-to-HTML conversion (MDEx with ammonia sanitization) with `[[double bracket]]` link syntax |
+| `Markdown` | Markdown-to-HTML conversion (MDEx with ammonia sanitization) with `[[double bracket]]` link syntax and streaming document support for chat |
 | `Duration` | Milliseconds to human-readable duration formatting |
 | `Auth` | Authentication plugs: login password check, API token validation, session enforcement |
 | `LiveHelpers.Params` | Pagination param parsing from URL query params |

lib/music_library_web/components/chat.ex

@@ -19,12 +19,18 @@ defmodule MusicLibraryWeb.Components.Chat do
      |> assign(:view, :active)
      |> assign(:chat, nil)
      |> assign(:chats, [])
+     |> assign(:streaming_doc, nil)
      |> assign(:has_history, false)}
   end
 
   @impl true
   def update(%{chunk: chunk}, socket) do
-    {:ok, update(socket, :current_response, &(&1 <> chunk))}
+    doc = socket.assigns.streaming_doc || Markdown.new_streaming_doc()
+
+    {:ok,
+     socket
+     |> update(:current_response, &(&1 <> chunk))
+     |> assign(:streaming_doc, MDEx.Document.put_markdown(doc, chunk))}
   end
 
   def update(%{done: true}, socket) do
@@ -36,6 +42,7 @@ defmodule MusicLibraryWeb.Components.Chat do
      socket
      |> update(:messages, &(&1 ++ [completed_message]))
      |> assign(:current_response, "")
+     |> assign(:streaming_doc, nil)
      |> assign(:loading, false)}
   end
 
@@ -207,7 +214,7 @@ defmodule MusicLibraryWeb.Components.Chat do
       phx-hook=".ScrollBottom"
     >
       <div
-        :if={@messages == [] and @current_response == ""}
+        :if={@messages == [] and @streaming_doc == nil}
         class="flex h-full flex-col items-center justify-center text-center text-zinc-500 dark:text-zinc-400"
       >
         <.icon
@@ -231,16 +238,16 @@ defmodule MusicLibraryWeb.Components.Chat do
       </div>
 
       <div
-        :if={@current_response != ""}
+        :if={@streaming_doc != nil}
         class="max-w-[85%] rounded-lg bg-zinc-100 px-4 py-2 text-sm text-zinc-900 dark:bg-zinc-700 dark:text-zinc-100"
       >
         <div class="dark:prose-invert prose prose-sm">
-          {raw(Markdown.to_html(@current_response))}
+          {raw(Markdown.streaming_to_html(@streaming_doc))}
         </div>
       </div>
 
       <div
-        :if={@loading and @current_response == ""}
+        :if={@loading and @streaming_doc == nil}
         class="flex items-center gap-2 text-zinc-500 dark:text-zinc-400"
       >
         <.loading class="size-4" />
@@ -306,6 +313,7 @@ defmodule MusicLibraryWeb.Components.Chat do
      socket
      |> assign(:messages, [])
      |> assign(:current_response, "")
+     |> assign(:streaming_doc, nil)
      |> assign(:error, nil)
      |> assign(:chat, nil)
      |> assign(:view, :active)}
@@ -329,6 +337,7 @@ defmodule MusicLibraryWeb.Components.Chat do
      |> assign(:chat, chat)
      |> assign(:messages, messages)
      |> assign(:current_response, "")
+     |> assign(:streaming_doc, nil)
      |> assign(:error, nil)
      |> assign(:view, :active)}
   end
@@ -346,6 +355,7 @@ defmodule MusicLibraryWeb.Components.Chat do
         |> assign(:chat, nil)
         |> assign(:messages, [])
         |> assign(:current_response, "")
+        |> assign(:streaming_doc, nil)
         |> assign(:error, nil)
       else
         socket
@@ -407,6 +417,7 @@ defmodule MusicLibraryWeb.Components.Chat do
      |> assign(:has_history, true)
      |> assign(:loading, true)
      |> assign(:current_response, "")
+     |> assign(:streaming_doc, nil)
      |> assign(:error, nil)}
   end
 

lib/music_library_web/markdown.ex

@@ -1,12 +1,19 @@
 defmodule MusicLibraryWeb.Markdown do
   @moduledoc """
-  Custom markdown processor that handles double square bracket links.
+  Custom markdown processor that handles double square bracket links
+  and streaming markdown rendering for chat.
 
   Text wrapped in double square brackets like `[[Foo]]` will be rendered as
   search links to the collection page.
   """
   alias MusicLibrary.Records
 
+  @mdex_options [
+    extension: [autolink: true, strikethrough: true, table: true],
+    render: [unsafe: true],
+    sanitize: MDEx.Document.default_sanitize_options()
+  ]
+
   @doc """
   Converts markdown with custom `[[link]]` syntax to HTML.
 
@@ -21,11 +28,7 @@ defmodule MusicLibraryWeb.Markdown do
         result =
           markdown_text
           |> process_double_bracket_links()
-          |> MDEx.to_html!(
+          |> MDEx.to_html!(@mdex_options)
-            extension: [autolink: true, strikethrough: true, table: true],
-            render: [unsafe: true],
-            sanitize: MDEx.Document.default_sanitize_options()
-          )
 
         {result, %{}}
       end
@@ -34,6 +37,29 @@ defmodule MusicLibraryWeb.Markdown do
 
   def to_html(nil), do: ""
 
+  @doc """
+  Creates a new streaming MDEx document for incremental markdown rendering.
+  """
+  @spec new_streaming_doc() :: MDEx.Document.t()
+  def new_streaming_doc do
+    MDEx.new([streaming: true] ++ @mdex_options)
+  end
+
+  @doc """
+  Renders a streaming MDEx document to HTML.
+  """
+  @spec streaming_to_html(MDEx.Document.t()) :: String.t()
+  def streaming_to_html(%MDEx.Document{} = doc) do
+    :telemetry.span(
+      [:markdown, :streaming_to_html],
+      %{},
+      fn ->
+        result = MDEx.to_html!(doc)
+        {result, %{}}
+      end
+    )
+  end
+
   @doc """
   Processes text to convert [[text]] patterns into markdown links.
 

test/music_library_web/markdown_test.exs

@@ -5,6 +5,40 @@ defmodule MusicLibraryWeb.MarkdownTest do
 
   doctest MusicLibraryWeb.Markdown
 
+  describe "streaming" do
+    test "new document renders empty string" do
+      doc = Markdown.new_streaming_doc()
+      assert Markdown.streaming_to_html(doc) == ""
+    end
+
+    test "incremental chunks produce valid HTML" do
+      doc = Markdown.new_streaming_doc()
+      doc = MDEx.Document.put_markdown(doc, "**bold")
+      html = Markdown.streaming_to_html(doc)
+      assert html =~ "<strong>bold</strong>"
+
+      doc = MDEx.Document.put_markdown(doc, " text**")
+      html = Markdown.streaming_to_html(doc)
+      assert html =~ "<strong>bold text</strong>"
+    end
+
+    test "handles incomplete code fences" do
+      doc = Markdown.new_streaming_doc()
+      doc = MDEx.Document.put_markdown(doc, "```elixir\nIO.puts")
+      html = Markdown.streaming_to_html(doc)
+      assert html =~ "IO"
+      assert html =~ "puts"
+      assert html =~ "<code"
+    end
+
+    test "sanitizes script tags" do
+      doc = Markdown.new_streaming_doc()
+      doc = MDEx.Document.put_markdown(doc, "<script>alert(1)</script>")
+      html = Markdown.streaming_to_html(doc)
+      refute html =~ "<script>"
+    end
+  end
+
   describe "to_html/1" do
     test "strips script tags" do
       result = Markdown.to_html("<script>alert('xss')</script>")