httputil: Centralize regexes based directly on RFCs

This will make it easier to stay in strict conformance with the RFCs.
Note that this commit makes a few small semantic changes to response
start-line parsing: status codes must be exactly three digits, and
control characters are not allowed in reason phrases.

Author: bdarnell

tornado/httputil.py

@@ -71,7 +71,32 @@
 # To be used with str.strip() and related methods.
 HTTP_WHITESPACE = " \t"
 
-HTTP_TOKEN_RE = re.compile(r"^[!#$%&'*+\-.^_`|~0-9A-Za-z]+$")
+
+class _ABNF:
+    """Class that holds a subset of ABNF rules from RFC 9110 and friends.
+
+    Class attributes are re.Pattern objects, with the same name as in the RFC
+    (with hyphens changed to underscores). Currently contains only the subset
+    we use (which is why this class is not public). Unfortunately the fields
+    cannot be alphabetized as they are in the RFCs because of dependencies.
+    """
+
+    # RFC 5234 (ABNF)
+    VCHAR = re.compile(r"[\x21-\x7E]")
+
+    # RFC 9110 (HTTP Semantics)
+    obs_text = re.compile(r"[\x80-\xFF]")
+    tchar = re.compile(r"[!#$%&'*+\-.^_`|~0-9A-Za-z]")
+    token = re.compile(rf"{tchar.pattern}+")
+    field_name = token
+
+    # RFC 9112 (HTTP/1.1)
+    HTTP_version = re.compile(r"HTTP/[0-9]\.[0-9]")
+    reason_phrase = re.compile(rf"(?:[\t ]|{VCHAR.pattern}|{obs_text.pattern})+")
+    status_code = re.compile(r"[0-9]{3}")
+    status_line = re.compile(
+        rf"({HTTP_version.pattern}) ({status_code.pattern}) ({reason_phrase.pattern})?"
+    )
 
 
 @lru_cache(1000)
@@ -145,7 +170,7 @@ def __init__(self, *args: typing.Any, **kwargs: str) -> None:  # noqa: F811
 
     def add(self, name: str, value: str) -> None:
         """Adds a new value for the given key."""
-        if not HTTP_TOKEN_RE.match(name):
+        if not _ABNF.token.fullmatch(name):
             raise HTTPInputError("Invalid header name %r" % name)
         norm_name = _normalize_header(name)
         self._last_key = norm_name
@@ -892,9 +917,6 @@ class RequestStartLine(typing.NamedTuple):
     version: str
 
 
-_http_version_re = re.compile(r"^HTTP/1\.[0-9]$")
-
-
 def parse_request_start_line(line: str) -> RequestStartLine:
     """Returns a (method, path, version) tuple for an HTTP 1.x request line.
 
@@ -909,10 +931,15 @@ def parse_request_start_line(line: str) -> RequestStartLine:
         # https://tools.ietf.org/html/rfc7230#section-3.1.1
         # invalid request-line SHOULD respond with a 400 (Bad Request)
         raise HTTPInputError("Malformed HTTP request line")
-    if not _http_version_re.match(version):
+    if not _ABNF.HTTP_version.fullmatch(version):
         raise HTTPInputError(
             "Malformed HTTP version in HTTP Request-Line: %r" % version
         )
+    if not version.startswith("HTTP/1"):
+        # HTTP/2 and above doesn't use parse_request_start_line.
+        # This could be folded into the regex but we don't want to deviate
+        # from the ABNF in the RFCs.
+        raise HTTPInputError("Unexpected HTTP version %r" % version)
     return RequestStartLine(method, path, version)
 
 
@@ -922,9 +949,6 @@ class ResponseStartLine(typing.NamedTuple):
     reason: str
 
 
-_http_response_line_re = re.compile(r"(HTTP/1.[0-9]) ([0-9]+) ([^\r]*)")
-
-
 def parse_response_start_line(line: str) -> ResponseStartLine:
     """Returns a (version, code, reason) tuple for an HTTP 1.x response line.
 
@@ -933,11 +957,14 @@ def parse_response_start_line(line: str) -> ResponseStartLine:
     >>> parse_response_start_line("HTTP/1.1 200 OK")
     ResponseStartLine(version='HTTP/1.1', code=200, reason='OK')
     """
-    line = native_str(line)
-    match = _http_response_line_re.match(line)
+    match = _ABNF.status_line.fullmatch(line)
     if not match:
         raise HTTPInputError("Error parsing response start line")
-    return ResponseStartLine(match.group(1), int(match.group(2)), match.group(3))
+    r = ResponseStartLine(match.group(1), int(match.group(2)), match.group(3))
+    if not r.version.startswith("HTTP/1"):
+        # HTTP/2 and above doesn't use parse_response_start_line.
+        raise HTTPInputError("Unexpected HTTP version %r" % r.version)
+    return r
 
 
 # _parseparam and _parse_header are copied and modified from python2.7's cgi.py