Request not closed with Unicode characters in headers

[kevin-mizu]

When responding with a unicode characters in a header key / value, it results in a UnicodeEncodeError (already known with #742, #1286...), but in addition, it doesn't close the connection, leading to use the body as a new request.

For example:

from flask import Flask, Response
app = Flask(__name__)

@app.route("/")
def index():
    return """<script>
fetch("/bug", { method: "POST", body: "GET /mizu HTTP/1.1\\r\\n\\r\\n" })
</script>"""

@app.route("/bug", methods=["POST", "GET"])
def bug():
    return Response("a", headers={ "x": "x\uffffx" })

app.run("0.0.0.0", 5000)

This will results in:

This comes from here > here > here. Because headers sending has already started when the error occurs, it will stop generating the response without reaching Connection: close and self.end_headers().

Environment:

• Python version: 3.9
• Werkzeug version: 3.0.1

[davidism]

I can't reproduce this issue. Using your application, I only see the first two requests (/ and /bug, but not /mizu). We added stream exhaustion in #2620, perhaps you're not actually testing on 3.0.1 like you've written?

Note that the development server must never be used in production. It is not designed to be particularly secure or robust to invalid use. It is only intended for local development.