new(libsinsp): add len() filter transformer

[LucaGuerra]

What type of PR is this?

Uncomment one (or more) /kind <> lines:

/kind feature

Any specific area of the project related to this PR?

Uncomment one (or more) /area <> lines:

/area libsinsp

Does this PR require a change in the driver versions?

No

What this PR does / why we need it:

This introduces a new len() transformer which acts like you'd expect:

• len(some_list) evaluates to the number of elements in the list
• len(some_string) evaluates to the length of the string (excluding null terminator of course)
• len(some_buffer) evaluates to the number of bytes in the buffer

This is also a handy way to check if lists are empty, since we couldn't do it before, which was apparent after a discussion with @leogr and @jasondellaluce .

Which issue(s) this PR fixes:

Fixes #2127

Special notes for your reviewer:

• The implementation slightly changes the transformer interface which now takes the element flags as well
• Do you see any potential corner cases with plugins?

Does this PR introduce a user-facing change?:

new(libsinsp): add len() filter transformer

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: LucaGuerra

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• OWNERS [LucaGuerra]

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[github-actions]

Perf diff from master - unit tests

     5.26%     -1.03%  [.] sinsp_parser::process_event
     4.49%     +0.95%  [.] next
     3.17%     +0.84%  [.] gzfile_read
     3.94%     -0.79%  [.] sinsp_evt::load_params
     6.15%     +0.71%  [.] sinsp::next
     1.70%     -0.62%  [.] libsinsp::sinsp_suppress::process_event
     1.32%     -0.56%  [.] sinsp_parser::event_cleanup
     5.20%     +0.55%  [.] sinsp_evt::get_type
     3.44%     +0.54%  [.] sinsp_thread_manager::get_thread_ref
     2.63%     +0.48%  [.] sinsp_thread_manager::find_thread

Heap diff from master - unit tests

peak heap memory consumption: -861B
peak RSS (including heaptrack overhead): 0B
total memory leaked: 0B

Heap diff from master - scap file

peak heap memory consumption: -32B
peak RSS (including heaptrack overhead): 0B
total memory leaked: 0B

Benchmarks diff from master

Comparing gbench_data.json to /root/actions-runner/_work/libs/libs/build/gbench_data.json
Benchmark                                                         Time             CPU      Time Old      Time New       CPU Old       CPU New
----------------------------------------------------------------------------------------------------------------------------------------------
BM_sinsp_split_mean                                            -0.0285         -0.0285           154           149           153           149
BM_sinsp_split_median                                          -0.0282         -0.0281           153           149           153           149
BM_sinsp_split_stddev                                          +0.9625         +0.9624             1             3             1             3
BM_sinsp_split_cv                                              +1.0201         +1.0199             0             0             0             0
BM_sinsp_concatenate_paths_relative_path_mean                  -0.0018         -0.0018            57            57            57            57
BM_sinsp_concatenate_paths_relative_path_median                -0.0019         -0.0020            57            57            57            57
BM_sinsp_concatenate_paths_relative_path_stddev                -0.2067         -0.2036             0             0             0             0
BM_sinsp_concatenate_paths_relative_path_cv                    -0.2054         -0.2022             0             0             0             0
BM_sinsp_concatenate_paths_empty_path_mean                     +0.0432         +0.0432            24            25            24            25
BM_sinsp_concatenate_paths_empty_path_median                   +0.0405         +0.0404            24            25            24            25
BM_sinsp_concatenate_paths_empty_path_stddev                   -0.2387         -0.2389             0             0             0             0
BM_sinsp_concatenate_paths_empty_path_cv                       -0.2702         -0.2704             0             0             0             0
BM_sinsp_concatenate_paths_absolute_path_mean                  -0.0302         -0.0302            56            55            56            55
BM_sinsp_concatenate_paths_absolute_path_median                -0.0389         -0.0389            56            54            56            54
BM_sinsp_concatenate_paths_absolute_path_stddev                +5.7276         +5.7165             0             1             0             1
BM_sinsp_concatenate_paths_absolute_path_cv                    +5.9373         +5.9259             0             0             0             0
BM_sinsp_split_container_image_mean                            -0.0110         -0.0110           398           393           398           393
BM_sinsp_split_container_image_median                          -0.0125         -0.0124           398           393           398           393
BM_sinsp_split_container_image_stddev                          +0.3031         +0.3030             2             2             2             2
BM_sinsp_split_container_image_cv                              +0.3177         +0.3176             0             0             0             0

[codecov]

Codecov Report

Attention: Patch coverage is 87.64940% with 31 lines in your changes missing coverage. Please review.

Project coverage is 74.60%. Comparing base (701e991) to head (5263f40).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
userspace/libsinsp/test/filter_transformer.ut.cpp	87.89%	23 Missing ⚠️
userspace/libsinsp/sinsp_filter_transformer.cpp	81.81%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2131      +/-   ##
==========================================
+ Coverage   74.46%   74.60%   +0.13%     
==========================================
  Files         254      254              
  Lines       33340    33458     +118     
  Branches     5724     5720       -4     
==========================================
+ Hits        24827    24961     +134     
+ Misses       8508     8470      -38     
- Partials        5       27      +22     

Flag	Coverage Δ
libsinsp	74.60% <87.64%> (+0.13%)	⬆️

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[FedeDP]

/milestone 0.19.0

[jasondellaluce]

Just last few concerns/questions

[LucaGuerra]

Thanks! Addressed comments

[poiana]

LGTM label has been added.

Git tree hash: a224ada55b3058be76302af4ac6ad6a1508ff483