Decode headers as UTF-8 also in ASGI (#2606)

Co-authored-by: Adam Hopkins <adam@amhopkins.com>

sanic/asgi.py

@@ -6,7 +6,7 @@ from typing import TYPE_CHECKING, Optional
 from urllib.parse import quote
 
 from sanic.compat import Header
-from sanic.exceptions import ServerError
+from sanic.exceptions import BadRequest, ServerError
 from sanic.helpers import Default
 from sanic.http import Stage
 from sanic.log import error_logger, logger
@@ -132,12 +132,20 @@ class ASGIApp:
         instance.sanic_app.state.is_started = True
         setattr(instance.transport, "add_task", sanic_app.loop.create_task)
 
-        headers = Header(
-            [
-                (key.decode("latin-1"), value.decode("latin-1"))
-                for key, value in scope.get("headers", [])
-            ]
-        )
+        try:
+            headers = Header(
+                [
+                    (
+                        key.decode("ASCII"),
+                        value.decode(errors="surrogateescape"),
+                    )
+                    for key, value in scope.get("headers", [])
+                ]
+            )
+        except UnicodeDecodeError:
+            raise BadRequest(
+                "Header names can only contain US-ASCII characters"
+            )
         path = (
             scope["path"][1:]
             if scope["path"].startswith("/")