scripts: new web server script

This provides a new script for serving the output of `yarn build`. This
is needed since the app now requires special http headers to be defined
to use certain web APIs.

Author: dlech

CONTRIBUTING.md

@@ -118,10 +118,10 @@ So for local testing without https, we need to follow
 To serve the website, run:
 
     yarn build
-    python3 -m http.server --directory build
+    ./scripts/serve.py
 
 Note: the usual `npx serve` doesn't properly serve parts of the site so we use
-Python instead.
+a custom Python script instead.
 
 Then at `chrome://flags/#unsafely-treat-insecure-origin-as-secure`, add:
 

scripts/serve.py

@@ -0,0 +1,34 @@
+#!/usr/bin/env python3
+
+"""
+Serve the build directory using builtin Python web server.
+"""
+
+import http.server
+import pathlib
+import socketserver
+
+BUILD_DIR = (pathlib.Path(__file__).parent.parent / "build").resolve()
+PORT = 8000
+
+
+class Handler(http.server.SimpleHTTPRequestHandler):
+    def __init__(
+        self,
+        request: bytes,
+        client_address: tuple[str, int],
+        server: socketserver.BaseServer,
+        directory: str | None = ...
+    ) -> None:
+        super().__init__(request, client_address, server, directory=BUILD_DIR)
+
+    def end_headers(self) -> None:
+        # custom headers needed for some web API features
+        self.send_header("Cross-Origin-Opener-Policy", "same-origin")
+        self.send_header("Cross-Origin-Embedder-Policy", "require-corp")
+        return super().end_headers()
+
+
+with socketserver.TCPServer(("", PORT), Handler) as httpd:
+    print(f"serving at http://0.0.0.0:{PORT}")
+    httpd.serve_forever()