[DEBUG-2972] Add initial support for Code Origin for Spans (Fastify entry spans only)

[watson]

What does this PR do?

Note: This PR relates to an upcoming Datadog feature that's not generally available yet.

This PR does two things:

• It lays the groundwork for a new feature called "Code Origin for Spans" (previously called "Span Origin").
• To showcase this feature, it adds limited support for just Fastify entry-spans.

To enable, set DD_CODE_ORIGIN_FOR_SPANS_ENABLED=true.

This feature will, in its most basic form, allow users to see where in their code base a span was started/created.

Code origin is only set for spans whos callstack contains user land stack frames.

For reference, here's a PR that implements Code Origin in the Java tracer: DataDog/dd-trace-java#7001

Motivation

This makes it easier to understand what each span shown in the flame graph represents.

Performance considerations

Keeping high performance in mind, we'll only compute the code origin for certain pre-defined span types. Specifically what we call entry and exit spans.

• Entry spans are defined as either the root span in a trace, or the "local" root span within a given service (it has a parent span, but that belongs to a different service).
• Exit spans are defined as spans "calling" out to other services, e.g. database spans, outgoing HTTP request spans etc.

Scope

Adding support for all types of entry and exist spans in a single PR will make it harder to review, so this PR will only concern itself with adding support for Fastify entry spans; That is spans representing incoming HTTP requests to a Fastify app.

Middlewares have to be handled in a special way, as a middleware might respond early to an incoming HTTP request in which case the route handler is never called. In that instance, we want to the code origin to point to where the middleware function was registered. Doing that for Fastify however, is out of scope of this PR and support for this will be added in an upcoming PR.

Note to reviewers

Since this feature has not yet been rolled out to staging, you need a hash-link to test it. If you need access, please contact me.

Tasks

• Benchmarks?

[github-actions]

Overall package size

Self size: 7.47 MB
Deduped: 63.24 MB
No deduping: 63.52 MB

Dependency sizes

| name | version | self size | total size | |------|---------|-----------|------------| | @datadog/native-appsec | 8.1.1 | 18.67 MB | 18.68 MB | | @datadog/native-iast-taint-tracking | 3.1.0 | 12.27 MB | 12.28 MB | | @datadog/pprof | 5.3.0 | 9.85 MB | 10.22 MB | | protobufjs | 7.2.5 | 2.77 MB | 5.16 MB | | @datadog/native-iast-rewriter | 2.5.0 | 2.51 MB | 2.59 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 | 1.8.0 | 1.21 MB | 1.21 MB | | jsonpath-plus | 9.0.0 | 580.4 kB | 1.03 MB | | import-in-the-middle | 1.11.2 | 112.74 kB | 826.22 kB | | msgpack-lite | 0.1.26 | 201.16 kB | 281.59 kB | | opentracing | 0.14.7 | 194.81 kB | 194.81 kB | | pprof-format | 2.1.0 | 111.69 kB | 111.69 kB | | @datadog/sketches-js | 2.1.0 | 109.9 kB | 109.9 kB | | semver | 7.6.3 | 95.82 kB | 95.82 kB | | lodash.sortby | 4.7.0 | 75.76 kB | 75.76 kB | | lru-cache | 7.14.0 | 74.95 kB | 74.95 kB | | ignore | 5.3.1 | 51.46 kB | 51.46 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 | | rfdc | 1.3.1 | 25.21 kB | 25.21 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 | | jest-docblock | 29.7.0 | 8.99 kB | 12.76 kB | | crypto-randomuuid | 1.0.0 | 11.18 kB | 11.18 kB | | koalas | 1.0.2 | 6.47 kB | 6.47 kB | | path-to-regexp | 0.1.10 | 6.38 kB | 6.38 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}

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-10-12 06:25:51

Comparing candidate commit 878d076 in PR branch watson/span-origin with baseline commit bd4aff5 in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 259 metrics, 7 unstable metrics.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 59.61%. Comparing base (7f93d36) to head (878d076).
Report is 10 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4449      +/-   ##
==========================================
- Coverage   69.19%   59.61%   -9.58%     
==========================================
  Files           1       36      +35     
  Lines         198     1617    +1419     
  Branches       33        0      -33     
==========================================
+ Hits          137      964     +827     
- Misses         61      653     +592     

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[watson]

• Add support for exit spans in Code Origin for Spans #4772
• [DEBUG-2972] Add initial support for Code Origin for Spans (Fastify entry spans only) #4449 👈
• master

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[shatzi]

very cool

[juan-fernandez]

LGTM. Only some minor comments

[juan-fernandez]

LGTM, but it might be worth waiting for some reviewer with more experience with the fastify plugin 😄