Fix promhttp error handling #726
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Essentially, just don't try to set a status code and send any error message in the body once metrics gathering has succeeded. At that point, the most likely reason for errors is anyway that the client has disconnected, in which sending an error is moot. The other possible reason for an error is a problem during metrics encoding. This is unlikely to happen (it's a coding error here in client_golang in any case), and if it is happening, the odds are we have already sent something to the ResponseWriter, which means we cannot set a status code anymore. The doc comment for HTTPErrorOnError now describes these circumstances explicitly and recommends to set a logger to report that kind of error. This should fix the reason for the infamous `superfluous response.WriteHeader call` message. Signed-off-by: beorn7 <beorn@grafana.com>
bwplotka
approved these changes
Mar 13, 2020
| // WriteHeader is called more than once, but we want to protect | ||
| // against it here. Note that we still delegate the WriteHeader | ||
| // to the original ResponseWriter to not mask the bug from it. | ||
| r.observeWriteHeader(code) |
|
Thanks @bwplotka 🐟 (o: I'll merge and cut a bug fix release. |
3 tasks
lidel
reviewed
Mar 24, 2020
| // WriteHeader is called more than once, but we want to protect | ||
| // against it here. Note that we still delegate the WriteHeader | ||
| // to the original ResponseWriter to not mask the bug from it. | ||
| r.observeWriteHeader(code) |
This was referenced Mar 16, 2021
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Essentially, just don't try to set a status code and send any error
message in the body once metrics gathering has succeeded. At that
point, the most likely reason for errors is anyway that the client has
disconnected, in which sending an error is moot. The other possible
reason for an error is a problem during metrics encoding. This is
unlikely to happen (it's a coding error here in client_golang in any
case), and if it is happening, the odds are we have already sent
something to the ResponseWriter, which means we cannot set a status
code anymore. The doc comment for HTTPErrorOnError now describes these
circumstances explicitly and recommends to set a logger to report that
kind of error.
This should fix the reason for the infamous
superfluous response.WriteHeader callmessage.@lidel @woodsaj