google
Add a way to test if a capture group has been defined in current scope
Hi
When using a syntax like ((?P<response_size>\d+)|-) on a line containing a - instead of a digit, the variable response_time is undefined. When attempting to use that variable, mtail throws an error.
This error can be reproduced using apache_common.mtail and testdata/apache-common.log
...or this simplified test
Program
counter total
/^[a-z]+ ((?P<response_size>\d+)|-)$/ {
$response_size > 0 {
total = $response_size
}
}
input log
test 99
test -
mtail output log
vm.go:92] test.mtail: Runtime error: strconv.ParseInt: parsing "": invalid syntax
vm.go:93] Error occurred at instruction 5 {s2i, <nil>}, originating in test.mtail at line 5
vm.go:95] Full input text from "log" was "test -"
I'am using mtail v3.0.0-rc33 (I tested rc16 and rc25 which have a similar behaviur)
I struggle to use that variable... all my attempts fails (I tried to use len(), or string()... but all fails.
As a workaround, I had to use an extra regex instead of checking the variable value
counter total
/^[a-z]+ ((?P<response_size>\d+)|-)$/ {
# check if the current line contains a digit (not a dash)
/ \d+$/ {
total = $response_size
}
}
It didn't match so the value is empty. Put the variable definition outside the | condition, and it will be either a number or a -.
In this case the capture group should be comparable to "" to know if it matched.
On Thu, 5 Sep 2019, 07:36 Frank lin Piat, [email protected] wrote:
I struggle to use that variable... all my attempts fails (I tried to use len(), or string()... but all fails.
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In this particular case it would work... But there are some other case where it is not possible.
We need to be able to test a variable no matter if it match or not.
The answer you came up with in https://github.com/google/mtail/issues/267#issuecomment-528097333 is the correct way to do this.
You've matched a field which is either a number or not a number. mtail can't parse the hyphen as a number, so it's up to you to tell it how to act. The inner condition will do the right thing at that point.
I can add this pattern to the documentation, possibly even make the error easier to understand; is there anything else you think mtail should do here?
OK I think the feature to add is that we need a way to test if a capture group is defined.
The current programme that works is to test the surrounding capture group content, but I admit tis does not make the pgramme very readable.