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gh-54930: Send a status line in error responses to malformed request lines #152980

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gh-54930: Send a status line in error responses to malformed request lines #152980

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6 changes: 5 additions & 1 deletion Lib/http/server.py
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Original file line number Diff line number Diff line change
Expand Up @@ -334,20 +334,23 @@ def parse_request(self):
raise ValueError("unreasonable length http version")
version_number = int(version_number[0]), int(version_number[1])
except (ValueError, IndexError):
# Send the error response with a status line and headers.
self.request_version = ''
self.send_error(
HTTPStatus.BAD_REQUEST,
"Bad request version (%r)" % version)
return False
self.request_version = version
if version_number >= (1, 1) and self.protocol_version >= "HTTP/1.1":
self.close_connection = False
if version_number >= (2, 0):
self.send_error(
HTTPStatus.HTTP_VERSION_NOT_SUPPORTED,
"Invalid HTTP version (%s)" % base_version_number)
return False
self.request_version = version

if not 2 <= len(words) <= 3:
self.request_version = ''
self.send_error(
HTTPStatus.BAD_REQUEST,
"Bad request syntax (%r)" % requestline)
Expand All @@ -356,6 +359,7 @@ def parse_request(self):
if len(words) == 2:
self.close_connection = True
if command != 'GET':
self.request_version = ''
self.send_error(
HTTPStatus.BAD_REQUEST,
"Bad HTTP/0.9 request type (%r)" % command)
Expand Down
15 changes: 15 additions & 0 deletions Lib/test/test_httpservers.py
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Original file line number Diff line number Diff line change
Expand Up @@ -386,6 +386,8 @@ def test_simple_get(self):
def test_invalid_request(self):
self.sock.send(b'POST /index.html\r\n')
res = self.sock.recv(1024)
# The error response is not sent in the bare HTTP/0.9 style.
self.assertStartsWith(res, b'HTTP/1.0 400 ')
self.assertIn(b"Bad HTTP/0.9 request type ('POST')", res)

def test_single_request(self):
Expand Down Expand Up @@ -1102,6 +1104,19 @@ def test_http_0_9(self):
self.assertEqual(result[0], b'<html><body>Data</body></html>\r\n')
self.verify_get_called()

@support.subTests('request,code', [
(b'GET / FUBAR\r\n\r\n', 400), # bad version
(b'GET / HTTP/2.0\r\n\r\n', 505), # unsupported version
(b'GET\r\n', 400), # bad syntax
(b'POST /\r\n', 400), # bad HTTP/0.9 request type
])
def test_request_line_error_has_status_line(self, request, code):
self.handler = SocketlessRequestHandler()
result = self.send_typical_request(request)
self.assertStartsWith(result[0], b'HTTP/1.1 %d ' % code)
self.verify_expected_headers(result[1:result.index(b'\r\n')])
self.assertFalse(self.handler.get_called)

def test_extra_space(self):
result = self.send_typical_request(
b'GET /spaced out HTTP/1.1\r\n'
Expand Down
5 changes: 5 additions & 0 deletions Misc/NEWS.d/next/Library/2026-07-03-21-10-00.gh-issue-54930.hq09Er.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
Error responses of :class:`http.server.BaseHTTPRequestHandler` to malformed
request lines now include a status line and headers instead of being sent in
the bare HTTP/0.9 style.
Only a valid HTTP/0.9 request (a two-word ``GET`` request line) now receives
an HTTP/0.9 style response.
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