Use capnp map for tracing metadata

[mgjm]

What type of PR is this?

/kind other

What this PR does / why we need it:

Currently (if tracing is enabled) the metadata field gets filled with a JSON encoded string map, that contains tracing metadata.

This PR changes this and uses capnp native maps and thereby eliminates the double encoding of JSON data inside of a capnp struct. Note that the proper way to implement maps in capnp is to use a List of string tuples.

Changes:

• Rename the existing metadata field to metadataOld
• Add a new metadata field of type List[StringStringMapEntry]
• Add utility functions to convert between a List of MapEntrys and rust types
• Remove serde_json from the server code
• Move capnp util function in go to capnp_util.go (slice and map encoding)
• Encode the metadata in the client in both formats (for backwards-compatibility)

Compatibility:

• I don't expect the conmon-rs server installed on a system to be newer than the client implementation.
• Eher the client and the server are installed with the same version (via os packages or installed from source)
• Or the client is newer (installed from source) and the server is older (installed via os packages)
• These cases are supported by the implemented backwards-compatibility in the client
• In the rare case that the server is on a newer version only tracing does not work (the server ignores the old field, everything else works as expected)

Which issue(s) this PR fixes:

None

Special notes for your reviewer:

Are those compatibility requirements acceptable?

Does this PR introduce a user-facing change?

None

[codecov-commenter]

Codecov Report

Merging #1498 (76b82fd) into main (03b7321) will decrease coverage by 0.18%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1498      +/-   ##
==========================================
- Coverage   34.71%   34.53%   -0.18%     
==========================================
  Files          13       13              
  Lines        1135     1135              
  Branches      394      391       -3     
==========================================
- Hits          394      392       -2     
  Misses        483      483              
- Partials      258      260       +2     

[mgjm]

Third time's the charm. Fixed now all typos and lints.

[haircommander]

@mgjm there's a merge conflict can you rebase please?

[haircommander]

/approve

LGTM

@saschagrunert PTAL

[saschagrunert]

The linter is not happy:

error: this argument is a mutable reference, but not used mutably
   --> conmon-rs/server/src/child_reaper.rs:364:45
    |
364 |     async fn spawn_cleanup_process(raw_cmd: &mut Vec<String>) {
    |                                             ^^^^^^^^^^^^^^^^ help: consider changing to: `&Vec<String>`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_pass_by_ref_mut
    = note: `-D clippy::needless-pass-by-ref-mut` implied by `-D warnings`

That's probably coming from a toolchain update.

[mgjm]

@saschagrunert Yeah, I haven't touched that code. Should I fix it anyway in this PR?

[saschagrunert]

@saschagrunert Yeah, I haven't touched that code. Should I fix it anyway in this PR?

Yes please, other PRs are affected by this as well.

[mgjm]

Btw, this lint is a false positive (or clippy is smart enough to detect that there is a non mutating alternative):

    async fn spawn_cleanup_process(raw_cmd: &mut Vec<String>) {
        let mut cleanup_cmd = Command::new(raw_cmd.remove(0));

raw_cmd.remove is mutating function. But we can replace this with a slice access.

[saschagrunert]

/lgtm

[openshift-ci]

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This pull-request has been approved by: haircommander, mgjm, saschagrunert

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