Re: [RFC PATCH 3/3] trace2: add a schema validator for trace2 events

[Josh Steadmon <steadmon@google.com>]

On 2019.06.12 15:18, Jeff King wrote:
> On Wed, Jun 12, 2019 at 09:23:41AM -0700, Josh Steadmon wrote:
> 
> > The problem with the existing validators is that they expect each file to be a
> > complete JSON entity, whereas the trace output is one object per line. You can
> > of course loop over the lines in a shell script, but in my testing this approach
> > took multiple hours on the full test suite trace output, vs. 15 minutes for the
> > implementation in this patch.
> 
> It seems like it should be easy to turn a sequence of entities into a
> single entity, with something like:
> 
>   echo '['
>   sed 's/$/,/' <one-per-line
>   echo ']'
> 
> You could even turn a sequence of files into a single entity (which
> might be even faster to validate, since it would be one invocation for
> the entire test suite) with something like:
> 
>   echo '{'
>   for fn in $FILES; do
> 	echo "\"$fn\": "
> 	cat $fn
> 	echo ","
>   done
>   echo '}'
> 
> though I suspect the resulting error messages might not be as good.
> 
> Obviously neither of those is particularly robust if the individual JSON
> is not well-formed. But then, if we are mostly interested in testing
> whether it's well-formed and expect it to be in the normal case, that
> might be a good optimization.

Yeah, as I noted in my reply to Ævar, ~20 of the trace lines generated by the
test suite are not properly encoded. So if we do something like:

  $ GIT_TRACE2_EVENT=$(pwd)/one-per-line make test
  $ (echo '[' ; sed 's/$/,/' < one-per-line ; echo ']') > list
  $ validate list

then most validators will only tell us that the file as a whole is malformed.
If we validate line-by-line, then we can just count how many malformed lines we
have and make sure it's within expectations.

Alternatively, we could just explicitly disable tracing on the tests that
generate the malformed traces.

> 
> I also wouldn't be surprised if "jq" could do this in a more robust way.

I'll go take a look at jq.

> -Peff