UnicodeEncodeError: ... surrogates not allowed

[dlucredativ]

$ cat app.py 
from starlette.applications import Starlette
from starlette.responses import JSONResponse
from starlette.routing import Route

external_data = {"Hello": 'World\udc82'}

async def homepage(request):
    return JSONResponse(external_data)

app = Starlette(debug=True, routes=[
    Route('/', homepage),
])

$ wget http://0.0.0.0:8000 -O -
--2025-12-30 13:10:10--  http://127.0.0.1:8000/
Connecting to 127.0.0.1:8000... connected.
HTTP request sent, awaiting response... 500 Internal Server Error
2025-12-30 13:10:10 ERROR 500: Internal Server Error.

$ uvicorn app:app
INFO:     Started server process [23478]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO:     127.0.0.1:56088 - "GET / HTTP/1.1" 500 Internal Server Error
ERROR:    Exception in ASGI application
Traceback (most recent call last):
  File "/tmp/venv/lib/python3.13/site-packages/uvicorn/protocols/http/httptools_impl.py", line 416, in run_asgi
    result = await app(  # type: ignore[func-returns-value]
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        self.scope, self.receive, self.send
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "/tmp/venv/lib/python3.13/site-packages/uvicorn/middleware/proxy_headers.py", line 60, in __call__
    return await self.app(scope, receive, send)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/venv/lib/python3.13/site-packages/starlette/applications.py", line 107, in __call__
    await self.middleware_stack(scope, receive, send)
  File "/tmp/venv/lib/python3.13/site-packages/starlette/middleware/errors.py", line 186, in __call__
    raise exc
  File "/tmp/venv/lib/python3.13/site-packages/starlette/middleware/errors.py", line 164, in __call__
    await self.app(scope, receive, _send)
  File "/tmp/venv/lib/python3.13/site-packages/starlette/middleware/exceptions.py", line 63, in __call__
    await wrap_app_handling_exceptions(self.app, conn)(scope, receive, send)
  File "/tmp/venv/lib/python3.13/site-packages/starlette/_exception_handler.py", line 53, in wrapped_app
    raise exc
  File "/tmp/venv/lib/python3.13/site-packages/starlette/_exception_handler.py", line 42, in wrapped_app
    await app(scope, receive, sender)
  File "/tmp/venv/lib/python3.13/site-packages/starlette/routing.py", line 716, in __call__
    await self.middleware_stack(scope, receive, send)
  File "/tmp/venv/lib/python3.13/site-packages/starlette/routing.py", line 736, in app
    await route.handle(scope, receive, send)
  File "/tmp/venv/lib/python3.13/site-packages/starlette/routing.py", line 290, in handle
    await self.app(scope, receive, send)
  File "/tmp/venv/lib/python3.13/site-packages/starlette/routing.py", line 78, in app
    await wrap_app_handling_exceptions(app, request)(scope, receive, send)
  File "/tmp/venv/lib/python3.13/site-packages/starlette/_exception_handler.py", line 53, in wrapped_app
    raise exc
  File "/tmp/venv/lib/python3.13/site-packages/starlette/_exception_handler.py", line 42, in wrapped_app
    await app(scope, receive, sender)
  File "/tmp/venv/lib/python3.13/site-packages/starlette/routing.py", line 75, in app
    response = await f(request)
               ^^^^^^^^^^^^^^^^
  File "/tmp/venv/demo/app.py", line 8, in homepage
    return JSONResponse(external_data)
  File "/tmp/venv/lib/python3.13/site-packages/starlette/responses.py", line 189, in __init__
    super().__init__(content, status_code, headers, media_type, background)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/venv/lib/python3.13/site-packages/starlette/responses.py", line 46, in __init__
    self.body = self.render(content)
                ~~~~~~~~~~~^^^^^^^^^
  File "/tmp/venv/lib/python3.13/site-packages/starlette/responses.py", line 198, in render
    ).encode("utf-8")
      ~~~~~~^^^^^^^^^
UnicodeEncodeError: 'utf-8' codec can't encode character '\udc82' in position 15: surrogates not allowed

I am aware of the following ugly workaround:

import json

from starlette.applications import Starlette
from starlette.responses import JSONResponse
from starlette.routing import Route

external_data = {"Hello": 'World\udc82'}

async def homepage(request):
    return JSONResponse(preprocess(external_data))

def preprocess(data):
    return json.loads(json.dumps(data, ensure_ascii=False).encode(errors='replace'))

app = Starlette(debug=True, routes=[
    Route('/', homepage),
])

$ wget http://127.0.0.1:8000 -q -O -
{"Hello":"World?"}