Fix --limit-request-line 0 to mean unlimited

Per documentation, limit_request_line=0 means unlimited. The code was
incorrectly treating 0 as "use default max" by checking <= 0 instead
of < 0.

For the fast C parser (gunicorn_h1c), which doesn't support 0 as
unlimited, pass a large value (1MB) instead. This applies to both
WSGI workers (http/message.py) and ASGI workers (asgi/protocol.py).

Fixes #3563

gunicorn/asgi/protocol.py

@@ -419,12 +419,18 @@ class ASGIProtocol(asyncio.Protocol):
             else:
                 parser_class = PythonProtocol
 
+        # Handle limit_request_line=0 (unlimited per documentation)
+        # PythonProtocol handles 0 correctly, but C parser needs a large value
+        limit_request_line = self.cfg.limit_request_line
+        if limit_request_line == 0 and parser_class != PythonProtocol:
+            limit_request_line = 1024 * 1024  # 1MB for C parser
+
         # Create parser with callbacks and limit parameters (both parsers support them)
         self._callback_parser = parser_class(
             on_headers_complete=self._on_headers_complete,
             on_body=self._on_body,
             on_message_complete=self._on_message_complete,
-            limit_request_line=self.cfg.limit_request_line,
+            limit_request_line=limit_request_line,
             limit_request_fields=self.cfg.limit_request_fields,
             limit_request_field_size=self.cfg.limit_request_field_size,
             permit_unconventional_http_method=self.cfg.permit_unconventional_http_method,

gunicorn/http/message.py

@@ -387,11 +387,19 @@ class Request(Message):
         self.query = None
         self.fragment = None
 
-        # get max request line size
+        # get max request line size (0 means unlimited per documentation)
         self.limit_request_line = cfg.limit_request_line
-        if (self.limit_request_line <= 0
-                or self.limit_request_line >= MAX_REQUEST_LINE):
+        if self.limit_request_line < 0:
             self.limit_request_line = MAX_REQUEST_LINE
+        # For fast parser: use large value when unlimited (0), since C parser
+        # doesn't support 0 as unlimited. 1MB should be more than enough.
+        if self.limit_request_line == 0:
+            self._fast_limit_request_line = 1024 * 1024  # 1MB
+        elif self.limit_request_line >= MAX_REQUEST_LINE:
+            self._fast_limit_request_line = MAX_REQUEST_LINE
+            self.limit_request_line = MAX_REQUEST_LINE
+        else:
+            self._fast_limit_request_line = self.limit_request_line
 
         self.req_number = req_number
         self.proxy_protocol_info = None
@@ -433,10 +441,11 @@ class Request(Message):
         while True:
             try:
                 # Pass all limit parameters to C parser
+                # Use _fast_limit_request_line which handles 0=unlimited
                 result = _fast_parser_module.parse_request(
                     data,
                     last_len=last_len,
-                    limit_request_line=self.limit_request_line,
+                    limit_request_line=self._fast_limit_request_line,
                     limit_request_fields=self.limit_request_fields,
                     limit_request_field_size=self.limit_request_field_size,
                     permit_unconventional_http_method=self.cfg.permit_unconventional_http_method,
@@ -447,7 +456,7 @@ class Request(Message):
                 last_len = len(data)
                 self.read_into(unreader, buf)
                 data = bytes(buf)
-                if len(data) > self.max_buffer_headers + self.limit_request_line:
+                if len(data) > self.max_buffer_headers + self._fast_limit_request_line:
                     raise LimitRequestHeaders("max buffer headers")
             except _fast_parser_module.LimitRequestLine as e:
                 raise LimitRequestLine(str(e))

tests/requests/invalid/limit_line_default_01.py

@@ -1,11 +0,0 @@
-#
-# This file is part of gunicorn released under the MIT license.
-# See the NOTICE for more information.
-
-from gunicorn.config import Config
-from gunicorn.http.errors import LimitRequestLine
-
-cfg = Config()
-# Setting limit_request_line=0 should use default max (8190)
-cfg.set('limit_request_line', 0)
-request = LimitRequestLine