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Improve logging for cancelled requests (#12587) 

Don't log stack traces for cancelled requests and use a custom HTTP
status code of 499.

Signed-off-by: Sean Quah <seanq@element.io>
This commit is contained in:
Sean Quah 2022-05-04 13:38:55 +01:00 committed by GitHub
parent 75dff3dc98
commit b2df0716bc
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3 changed files with 32 additions and 1 deletions
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1
changelog.d/12587.misc Normal file
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@ -0,0 +1 @@
Add `@cancellable` decorator, for use on endpoint methods that can be cancelled when clients disconnect.

2
docs/usage/administration/request_log.md
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@ -28,7 +28,7 @@ See the following for how to decode the dense data available from the default lo
| NNNN | Total time waiting for response to DB queries across all parallel DB work from this request |
| OOOO | Count of DB transactions performed |
| PPPP | Response body size |
| QQQQ | Response status code (prefixed with ! if the socket was closed before the response was generated) |
| QQQQ | Response status code<br/>Suffixed with `!` if the socket was closed before the response was generated.<br/>A `499!` status code indicates that Synapse also cancelled request processing after the socket was closed.<br/> |
| RRRR | Request |
| SSSS | User-agent |
| TTTT | Events fetched from DB to service this request (note that this does not include events fetched from the cache) |

30
synapse/http/server.py
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@ -43,6 +43,7 @@ from typing_extensions import Protocol
from zope.interface import implementer
from twisted.internet import defer, interfaces
from twisted.internet.defer import CancelledError
from twisted.python import failure
from twisted.web import resource
from twisted.web.server import NOT_DONE_YET, Request
@ -82,6 +83,14 @@ HTML_ERROR_TEMPLATE = """<!DOCTYPE html>
</html>
"""
# A fictional HTTP status code for requests where the client has disconnected and we
# successfully cancelled the request. Used only for logging purposes. Clients will never
# observe this code unless cancellations leak across requests or we raise a
# `CancelledError` ourselves.
# Analogous to nginx's 499 status code:
# https://github.com/nginx/nginx/blob/release-1.21.6/src/http/ngx_http_request.h#L128-L134
HTTP_STATUS_REQUEST_CANCELLED = 499
def return_json_error(f: failure.Failure, request: SynapseRequest) -> None:
"""Sends a JSON error response to clients."""
@ -93,6 +102,17 @@ def return_json_error(f: failure.Failure, request: SynapseRequest) -> None:
error_dict = exc.error_dict()
logger.info("%s SynapseError: %s - %s", request, error_code, exc.msg)
elif f.check(CancelledError):
error_code = HTTP_STATUS_REQUEST_CANCELLED
error_dict = {"error": "Request cancelled", "errcode": Codes.UNKNOWN}
if not request._disconnected:
logger.error(
"Got cancellation before client disconnection from %r: %r",
request.request_metrics.name,
request,
exc_info=(f.type, f.value, f.getTracebackObject()), # type: ignore[arg-type]
)
else:
error_code = 500
error_dict = {"error": "Internal server error", "errcode": Codes.UNKNOWN}
@ -155,6 +175,16 @@ def return_html_error(
request,
exc_info=(f.type, f.value, f.getTracebackObject()), # type: ignore[arg-type]
)
elif f.check(CancelledError):
code = HTTP_STATUS_REQUEST_CANCELLED
msg = "Request cancelled"
if not request._disconnected:
logger.error(
"Got cancellation before client disconnection when handling request %r",
request,
exc_info=(f.type, f.value, f.getTracebackObject()), # type: ignore[arg-type]
)
else:
code = HTTPStatus.INTERNAL_SERVER_ERROR
msg = "Internal server error"