PEP 594 has cgi module scheduled for deprecation in Python 3.8. Reimplement

cgi.parse_header in Sanic. The new implementation is much faster than either
cgi.parse_header or equivalent werkzeug.parse_options_header, and unlike the
two, handles also quoted values with semicolons or \" in them.

sanic/headers.py

@@ -0,0 +1,18 @@
+import re
+
+token, quoted = r"([\w!#$%&'*+\-.^_`|~]+)", r'"((?:[^"]|\\")*)"'
+parameter = re.compile(f';\s*{token}=(?:{token}|{quoted})', re.ASCII)
+
+
+def parse_options_header(value: str):
+    """Parse HTTP header values of Content-Type format."""
+    pos = value.find(';')
+    if pos == -1:
+        options = {}
+    else:
+        options = {
+            m.group(1).lower(): m.group(2) or m.group(3).replace(r'\"', '"')
+            for m in parameter.finditer(value[pos:])
+        }
+        value = value[:pos]
+    return value.strip().lower(), options

sanic/request.py

@@ -4,7 +4,6 @@ import json
 import sys
 import warnings
 
-from cgi import parse_header
 from collections import defaultdict, namedtuple
 from http.cookies import SimpleCookie
 from urllib.parse import parse_qs, parse_qsl, unquote, urlunparse
@@ -13,7 +12,7 @@ from httptools import parse_url
 
 from sanic.exceptions import InvalidUsage
 from sanic.log import error_logger, logger
-
+from sanic.headers import parse_options_header
 
 try:
     from ujson import loads as json_loads
@@ -177,7 +176,7 @@ class Request(dict):
             content_type = self.headers.get(
                 "Content-Type", DEFAULT_HTTP_CONTENT_TYPE
             )
-            content_type, parameters = parse_header(content_type)
+            content_type, parameters = parse_options_header(content_type)
             try:
                 if content_type == "application/x-www-form-urlencoded":
                     self.parsed_form = RequestParameters(
@@ -551,7 +550,7 @@ def parse_multipart_form(body, boundary):
 
             colon_index = form_line.index(":")
             form_header_field = form_line[0:colon_index].lower()
-            form_header_value, form_parameters = parse_header(
+            form_header_value, form_parameters = parse_options_header(
                 form_line[colon_index + 2 :]
             )