Fix posit-dev#1601: Force text/javascript for .js files

Author: jcheng5

CHANGELOG.md

@@ -31,7 +31,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 * `ui.notification_show(duration=None)` now persists the notification until the app user closes it. (#1577)
 
-### Bug fixes
+* Some copies of Windows 10 have registry entries mapping .js files to content type "text/plain", which was causing all sorts of problems for browsers.
 
 ### Deprecations
 

shiny/_utils.py

@@ -82,6 +82,12 @@ def guess_mime_type(
     """
     # Note that in the parameters above, "os.PathLike[str]" is in quotes to avoid
     # "TypeError: 'ABCMeta' object is not subscriptable", in Python<=3.8.
+    if url:
+        # Work around issue #1601, some installations of Windows 10 return text/plain
+        # as the mime type for .js files
+        _, ext = os.path.splitext(os.fspath(url))
+        if ext.lower() in [".js", ".mjs", ".cjs"]:
+            return "text/javascript"
     return mimetypes.guess_type(url, strict)[0] or default
 
 

shiny/http_staticfiles.py

@@ -12,6 +12,9 @@
 from __future__ import annotations
 
 import re
+from typing import Any
+
+from . import _utils
 
 __all__ = (
     "StaticFiles",
@@ -24,13 +27,32 @@
 
 if "pyodide" not in sys.modules:
     # Running in native mode; use starlette StaticFiles
+    import os
 
     import starlette.responses
     import starlette.staticfiles
 
-    StaticFiles = starlette.staticfiles.StaticFiles  # type: ignore
     FileResponse = starlette.responses.FileResponse  # type: ignore
 
+    # Wrapper for StaticFiles to fix .js content-type issues on Windows 10 (see #1601)
+    class StaticFiles(starlette.staticfiles.StaticFiles):  # type: ignore
+        def file_response(
+            self,
+            full_path: str | os.PathLike[str],
+            *args: Any,
+            **kwargs: Any,
+        ) -> starlette.responses.Response:
+            resp = super().file_response(full_path, *args, **kwargs)
+            if resp.headers["content-type"].startswith("text/plain"):
+                correct_type = _utils.guess_mime_type(full_path)
+                resp.headers["content-type"] = (
+                    f"{correct_type}; charset={resp.charset}"
+                    if correct_type.startswith("text/")
+                    else correct_type
+                )
+                resp.media_type = correct_type
+            return resp
+
 else:
     # Running in wasm mode; must use our own simple StaticFiles
 
@@ -43,8 +65,6 @@
     from starlette.responses import PlainTextResponse
     from starlette.types import Receive, Scope, Send
 
-    from . import _utils
-
     class StaticFiles:
         dir: pathlib.Path
         root_path: str