Make HttpHeaders strings const

[jonapoul]

Subsystem ktor-http

Motivation Primarily to help make these strings usable in compile-time contexts, e.g. as annotation parameters. The MayBeConstant suppression makes me think there might be a reason for them not being const already, but I couldn't find any reasoning for that besides ABI compatibility.

Solution Make immutable strings const.

[coderabbitai[bot]]

Walkthrough

Header-name declarations in io.ktor.http.HttpHeaders were converted from runtime vals/getters to compile-time const val constants; many deprecated getter-style accessors and underscored aliases were added for compatibility; UnsafeHeaders and UnsafeHeadersList were introduced and API/klib metadata updated.

Changes

Cohort / File(s)	Summary
Const migration (source + APIs) ktor-http/common/src/io/ktor/http/HttpHeaders.kt, ktor-http/api/ktor-http.api, ktor-http/api/ktor-http.klib.api	Many HTTP header declarations moved from runtime val/getter forms to const val compile-time constants (e.g., ALPN, Accept, AcceptCharset, …, XTotalCount). API and klib metadata updated to reflect const qualifiers.
Deprecated getter aliases & underscored properties ktor-http/common/src/io/ktor/http/HttpHeaders.kt	Added deprecated getter-style accessors and underscored alias properties with @get:JvmName and @Deprecated(..., ReplaceWith(...)) returning the new constants to preserve existing usages.
Unsafe headers additions ktor-http/common/src/io/ktor/http/HttpHeaders.kt, ktor-http/api/ktor-http.klib.api	Introduced UnsafeHeaders: Array<String> and UnsafeHeadersList: List<String> as public members with accessors; exported in klib API metadata.
API cleanup — removed JVM getters ktor-http/api/ktor-http.api	Removed many per-header getter functions (e.g., getAccept(), getContentType(), …) in favor of public string fields/constants (reflected in the JVM API file).
Annotations / suppressions ktor-http/common/src/io/ktor/http/HttpHeaders.kt	Updated @Suppress to include ConstPropertyName and adjusted JVM name annotations and deprecation metadata formatting.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

• Review focus:
  • Verify deprecated alias getters preserve JVM getter names/signatures exactly.
  • Confirm API/klib metadata matches source changes (const vs val, removed getters).
  • Check ReplaceWith expressions and @get:JvmName annotations for accuracy.
  • Inspect initialization, visibility, and contents of UnsafeHeaders / UnsafeHeadersList.

Suggested reviewers

• bjhham

Pre-merge checks and finishing touches

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 1.00% which is insufficient. The required threshold is 80.00%.	You can run @coderabbitai generate docstrings to improve docstring coverage.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description follows the template structure with all required sections (Subsystem, Motivation, Solution) completed. It clearly explains the problem, rationale, and solution.
Title check	✅ Passed	The title clearly and concisely summarizes the main change: converting HttpHeaders string values from mutable vals to compile-time constants (const).

✨ Finishing touches

• [ ] 📝 Generate docstrings

🧪 Generate unit tests (beta)

• [ ] Create PR with unit tests
• [ ] Post copyable unit tests in a comment

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[bjhham]

but I couldn't find any reasoning for that besides ABI compatibility.

This is actually quite important... Perhaps there is a way to preserve compatibility via Jvm annotations or something?

[osipxd]

YouTrack issue: KTOR-9199 Make HttpHeaders strings const