Fix iast metrics memory leak

[iunanua]

What does this PR do?

Do not invoke globalNamespace.count when merging request metrics.

There are two kind of metrics collected by the iast: global and request metrics. In both cases IastNamespace is used.

IastNamespace overrides Namespace.count to cache metrics and uses the metric tags as the cache key.
When finalizing the request, stored request metrics are merged into globalNamespace in order to be sent via telemetry.
And as globalNamespace never has a request metric cached it stores the metric automatically causing a leak.

Motivation

Fix iast metrics memory leak introduced in #4017

Plugin Checklist

• Unit tests.
• TypeScript definitions.
• TypeScript tests.
• API documentation.
• CircleCI jobs/workflows.
• Plugin is exported.

Additional Notes

Security

Datadog employees:

• If this PR touches code that signs or publishes builds or packages, or handles credentials of any kind, I've requested a review from @DataDog/security-design-and-guidance.
• This PR doesn't touch any of that.

Unsure? Have a question? Request a review!

[github-actions]

Overall package size

Self size: 6.24 MB
Deduped: 61.19 MB
No deduping: 61.94 MB

Dependency sizes

name	version	self size	total size
@datadog/native-iast-taint-tracking	1.7.0	16.71 MB	16.72 MB
@datadog/native-appsec	7.1.0	14.37 MB	14.38 MB
@datadog/pprof	5.1.0	8.83 MB	9.68 MB
protobufjs	7.2.5	2.77 MB	6.56 MB
@datadog/native-iast-rewriter	2.3.0	2.15 MB	2.24 MB
@opentelemetry/core	1.14.0	872.87 kB	1.47 MB
@datadog/native-metrics	2.0.0	898.77 kB	1.3 MB
@opentelemetry/api	1.4.1	780.32 kB	780.32 kB
import-in-the-middle	1.7.3	67.62 kB	731.01 kB
pprof-format	2.0.7	588.12 kB	588.12 kB
msgpack-lite	0.1.26	201.16 kB	281.59 kB
opentracing	0.14.7	194.81 kB	194.81 kB
semver	7.5.4	93.4 kB	123.8 kB
@datadog/sketches-js	2.1.0	109.9 kB	109.9 kB
lodash.sortby	4.7.0	75.76 kB	75.76 kB
lru-cache	7.14.0	74.95 kB	74.95 kB
ipaddr.js	2.1.0	60.23 kB	60.23 kB
ignore	5.2.4	51.22 kB	51.22 kB
int64-buffer	0.1.10	49.18 kB	49.18 kB
shell-quote	1.8.1	44.96 kB	44.96 kB
istanbul-lib-coverage	3.2.0	29.34 kB	29.34 kB
tlhunter-sorted-set	0.1.0	24.94 kB	24.94 kB
limiter	1.1.5	23.17 kB	23.17 kB
dc-polyfill	0.1.4	23.1 kB	23.1 kB
retry	0.13.1	18.85 kB	18.85 kB
node-abort-controller	3.1.1	16.89 kB	16.89 kB
jest-docblock	29.7.0	8.99 kB	12.76 kB
crypto-randomuuid	1.0.0	11.18 kB	11.18 kB
path-to-regexp	0.1.7	6.78 kB	6.78 kB
koalas	1.0.2	6.47 kB	6.47 kB
methods	1.1.2	5.29 kB	5.29 kB
module-details-from-path	1.0.3	4.47 kB	4.47 kB

_{🤖 This report was automatically generated by heaviest-objects-in-the-universe}

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.22%. Comparing base (bc78d8b) to head (f0b049d).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4185   +/-   ##
=======================================
  Coverage   85.22%   85.22%           
=======================================
  Files         247      247           
  Lines       10948    10954    +6     
  Branches       33       33           
=======================================
+ Hits         9330     9336    +6     
  Misses       1618     1618           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-03-26 09:48:34

Comparing candidate commit f0b049d in PR branch igor/fix-iast-metrics-leak with baseline commit bc78d8b in branch master.

Found 2 performance improvements and 0 performance regressions! Performance is the same for 260 metrics, 4 unstable metrics.

scenario:plugin-graphql-with-depth-and-collapse-on-18

• 🟩 max_rss_usage [-126.321MB; -112.443MB] or [-13.297%; -11.836%]

scenario:plugin-graphql-with-depth-off-18

• 🟩 max_rss_usage [-99.352MB; -90.344MB] or [-10.647%; -9.682%]

[uurien]

to.be.equal( is more used than eq

Suggested change

	expect(namespace.iastMetrics.size).to.be.eq(0)
	expect(namespace.metrics.size).to.be.eq(0)
	expect(namespace.distributions.size).to.be.eq(0)
	expect(namespace.iastMetrics.size).to.be.equal(0)
	expect(namespace.metrics.size).to.be.equal(0)
	expect(namespace.distributions.size).to.be.equal(0)

[uurien]

We talked yesterday about changing metrics = new Map() in line 64 by metrics = new WeakMap() to be 100% sure that the map is not going to increase to infinity.

[iunanua]

I cannot use a WeakMap because:

• tags are cached so they will never be collected by GC
• i need to iterate the map values

Instead, I set a max size for the Map and check the size to ensure it

[iunanua]

Here

The max size should never be reached but just in case...