check_http sometimes fails when Transfer-Encoding: chunked is used

[chgarling]

Sometimes check_http goes into CRITICAL state when Transfer-Encoding: chunked is used. Then the check fails for a couple of minutes.

We have spent some time with debugging but the response we get from the webserver is always complete. If we choose another string to check the content the check is fine again. So it looks like check_http has a problem with reassembling the chunked response.

We are using nagios-plugins-http-2.2.1-4git.el7.x86_64 on CentOS Linux release 7.4.1708 (Core).

The used command is as followed (anonymized):
check_http -H "www.example.com" -I "192.168.90.107" -c 20 -e 200 -k "https:true" -p 8810 -s "Realisiert mit dem Government Site Builder" -u /Webs/Example/DE/Startseite/startseite_node.html -w 10

The flapping check output looks like this:
HTTP OK: Status line output matched "200" - HTTP/1.1 200 OK - 60925 bytes in 0.005 second response time |time=0.005078s;10.000000;20.000000;0.000000 size=60925B;;;0
HTTP CRITICAL: Status line output matched "200" - HTTP/1.1 200 OK - string 'Realisiert mit dem Governm...' not found on 'http://www.example.com:8810/Webs/Example/DE/Startseite/startseite_node.html' - 71720 bytes in 0.090 second response time |time=0.089791s;10.000000;20.000000;0.000000 size=71720B;;;0

Here you can find two straces that also show the problem:

strace-check_http-s407-8810.gz
strace-check_http-s409-8810.gz

The string is read in the server reply in strace:
"<!--Realisiert mit dem Government Site Builder"

But it still outputs:
write(1, "HTTP CRITICAL: Status line output matched "200" - HTTP/1.1 200 OK - string 'Realisiert mit dem Governm...' not found on 'http://www.example.com:8810/Webs/Example/DE/Startseite/startseite_node.html'

If you need further information, logs or anything else let me know.

Regards, Christian

[waja]

We are using nagios-plugins-http-2.2.1-4git.el7.x86_64 on CentOS Linux release 7.4.1708 (Core).

This plugins are not our ones but you can ask the guys over there at https://github.com/nagios-plugins/nagios-plugins.

[ChrisSLR]

We have the same issue with

 check_http v2.2 (monitoring-plugins 2.2)

If a chunk end is within the search string the check will fail because of the hex size information in the response.

One workaround is to use HTTP 1.0 by connecting to the Server using -I and providing the hostname as a -k "host: www.mydomain.com". HTTP 1.0 doesn't support chunks. Because of a bug in the header handling code in check_http it is necessary not to write "Host:". Using "HOST:" or "host:" is ok.

[craig]

Thanks for the hint, the bug is relevant for nagios-plugins and monitoring-plugins. nagios-plugins/nagios-plugins#374

[ekeih]

Additionally to a lot of other stuff check_curl solves the chunking issues: #1535