Add log.fetch() HTTP auto-instrumentation and W3C traceparent propaga…

[lillem4n]

…tion (v2.3.0)

Summary by CodeRabbit

• New Features

  • Added log.fetch() method as a drop-in fetch replacement with automatic HTTP tracing and OpenTelemetry span creation
  • Implemented W3C trace context propagation for distributed tracing across services
  • Added configuration options to capture request/response headers and query strings (with redaction support)
  • New helper functions for trace context header formatting and parsing

• Documentation

  • Updated documentation with usage examples and configuration details for HTTP tracing

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 71713b11-eb48-45a7-9c5d-eaf4acb38b8c

📥 Commits

Reviewing files that changed from the base of the PR and between 7c49272 and 3ed081d.

⛔ Files ignored due to path filters (1)

• package-lock.json is excluded by !**/package-lock.json

📒 Files selected for processing (4)

• README.md
• index.ts
• package.json
• test.ts

📝 Walkthrough

Walkthrough

Version 2.3.0 adds W3C trace context support to the log library. Two new exported helpers (formatTraceparent, parseTraceparent) are introduced. The Log constructor gains optional incoming traceparent adoption, clone() is updated to avoid re-adopting it, and a new log.fetch() method wraps globalThis.fetch to create OTLP CLIENT spans with HTTP attribute recording, query redaction, header allow-lists, and error status mapping.

Changes

log.fetch() auto-instrumentation and W3C trace context propagation

Layer / File(s)	Summary
LogConf/LogInt type extensions and trace context helpers index.ts	LogConf adds captureQuery, captureRequestHeaders, captureResponseHeaders, and traceparent fields; LogInt adds the traceparent() method signature; formatTraceparent() and parseTraceparent() are exported.
Log constructor traceparent adoption and clone() isolation index.ts	Constructor parses conf.traceparent when no parentLog is present, using parsed trace/span IDs during span init; clone() excludes traceparent from inherited config.
log.fetch() wrapper and URL/query helpers index.ts	Adds SENSITIVE_QUERY_KEYS and buildUrlFull() for query redaction, then implements Log.traceparent() and Log.fetch(), which create a nested CLIENT span, inject traceparent headers, record OTel HTTP attributes with optional header capture, set error status on failures, and export the span asynchronously.
Test harness updates and new traceparent/fetch tests test.ts	okResponse gains Headers, fetchResponse helper is added, stubFetch records request headers, callHeader() and clientSpan() helpers are added; new test blocks cover formatTraceparent/parseTraceparent round-trips, traceparent adoption/precedence/clone behavior, and all log.fetch() scenarios.
README, AGENTS.md docs and version bump README.md, AGENTS.md, package.json	README adds log.fetch() usage, trace continuation docs, new config options, and a v2.3.0 changelog entry; AGENTS.md description is expanded; package version is bumped to 2.3.0.

Sequence Diagram(s)

sequenceDiagram
  participant Caller
  participant LogFetch as log.fetch
  participant globalFetch as globalThis.fetch
  participant OTLP as OTLP /v1/traces

  Caller->>LogFetch: fetch(url, init)
  LogFetch->>LogFetch: create nested CLIENT span
  LogFetch->>LogFetch: inject traceparent into request headers
  LogFetch->>LogFetch: buildUrlFull - redact or strip query
  LogFetch->>globalFetch: forward request
  globalFetch-->>LogFetch: Response or network error
  LogFetch->>LogFetch: record HTTP attrs and url.full
  LogFetch->>LogFetch: set error status on 4xx or 5xx
  LogFetch->>OTLP: export CLIENT span async via log.end()
  LogFetch-->>Caller: return Response or rethrow

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Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Possibly related PRs

• larvit/log#178: Modifies Log.end() to await OTLP exports with a timeout — directly relevant because this PR's log.fetch() CLIENT spans rely on that same flush path.
• larvit/log#179: Updates test.ts fetch stubbing and OTLP payload assertions — the same test infrastructure this PR further extends for log.fetch() and traceparent tests.

Poem

🐇 Hoppity-hop through the network I go,
Wrapping each fetch with a span in tow,
traceparent headers injected with care,
Query strings redacted — your secrets stay there,
CLIENT spans exported, the trace flows complete,
🌐 Distributed tracing — now isn't that neat!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main changes: adding log.fetch() HTTP auto-instrumentation and W3C traceparent propagation, which directly align with the PR's primary objectives and file changes.
Docstring Coverage	✅ Passed	Docstring coverage is 83.33% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/fetch-auto-instrumentation

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[coderabbitai]

Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@AGENTS.md`:
- Line 7: The documentation in AGENTS.md overstates the auto-instrumentation
behavior of log.fetch(). Update line 7 to clarify that log.fetch() only
auto-instruments outgoing HTTP requests when provided with string or URL inputs
(as defined by the Log.fetch(input: string | URL) signature in index.ts), and
that other input shapes fall back to raw fetch without creating a client span.
This will accurately reflect the narrower contract of the implementation and
prevent agents from relying on instrumentation that is not guaranteed for all
fetch input types.

In `@README.md`:
- Around line 73-88: The README documentation overstates the capabilities of
log.fetch() by claiming it is a full drop-in replacement for fetch(). However,
based on the actual implementation in index.ts, log.fetch() only supports string
or URL inputs; when given a Request object, it falls back to plain fetch()
without instrumentation. Revise the documentation to clarify that log.fetch() is
a drop-in replacement only for string/URL based fetch calls, and note that
Request-based inputs will not receive OpenTelemetry instrumentation or trace
header injection.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 50faa494-cebf-40da-8e31-97e10a222b99

📥 Commits

Reviewing files that changed from the base of the PR and between 63d85df and 7c49272.

⛔ Files ignored due to path filters (1)

• package-lock.json is excluded by !**/package-lock.json

📒 Files selected for processing (5)

• AGENTS.md
• README.md
• index.ts
• package.json
• test.ts