🔥 feat: Add support for configuring the Regex engine on the router by Claude · Pull Request #4254 · gofiber/fiber

Claude · 2026-05-04T22:40:45Z

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

This section details on the original issue you should resolve

<issue_title>📝 [Proposal]: ability to use alternative regex for router</issue_title>
<issue_description>### Feature Proposal Description

This is a substantially faster assembly optimised regex package that is drop in replacement: https://github.com/coregx/coregex

Alignment with Express API

Na

HTTP RFC Standards Compliance

Na

API Stability

Na

Feature Examples
Na
Checklist:

I agree to follow Fiber's Code of Conduct.

I have searched for existing issues that describe my proposal before opening this one.

I understand that a proposal that does not meet these guidelines may be closed without explanation.</issue_description>

Comments on the Issue (you are @claude[agent] in this section)

- Created RegexEngine and RegexCompiler interfaces - Updated path.go to use configured regex engine - Added RegexEngine field to Config with DefaultRegexEngine - Updated router.go to pass RegexEngine to parseRoute - Added comprehensive tests for regex abstraction - Created example showing how to integrate coregex Agent-Logs-Url: https://github.com/gofiber/fiber/sessions/3e2b7990-e9c5-41f6-afbf-ad29c8bbcfd0 Co-authored-by: gaby <835733+gaby@users.noreply.github.com>

codecov · 2026-05-04T22:58:32Z

Codecov Report

❌ Patch coverage is 89.79592% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.35%. Comparing base (da9b7b6) to head (f9d2dcc).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
path.go	88.88%	2 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4254      +/-   ##
==========================================
- Coverage   91.35%   91.35%   -0.01%     
==========================================
  Files         132      132              
  Lines       12977    13066      +89     
==========================================
+ Hits        11855    11936      +81     
- Misses        708      713       +5     
- Partials      414      417       +3

Flag	Coverage Δ
unittests	`91.35% <89.79%> (-0.01%)`	⬇️

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Agent-Logs-Url: https://github.com/gofiber/fiber/sessions/3e2b7990-e9c5-41f6-afbf-ad29c8bbcfd0 Co-authored-by: gaby <835733+gaby@users.noreply.github.com>

- Added regex-engines.md guide with coregex integration examples - Documented RegexEngine and RegexCompiler interfaces - Included performance benchmarks and use cases - Added custom implementation examples Agent-Logs-Url: https://github.com/gofiber/fiber/sessions/3e2b7990-e9c5-41f6-afbf-ad29c8bbcfd0 Co-authored-by: gaby <835733+gaby@users.noreply.github.com>

gaby · 2026-05-04T23:25:21Z

@claude[agent]

fix markdownlint issues
remove examples folder

- Removed examples/regex-engine folder as requested - Updated docs/guide/regex-engines.md to remove reference to examples folder - All markdown linting issues resolved Agent-Logs-Url: https://github.com/gofiber/fiber/sessions/9e71d891-0cc3-4786-8921-d994e500db6f Co-authored-by: gaby <835733+gaby@users.noreply.github.com>

Claude · 2026-05-04T23:28:30Z

@claude[agent]

fix markdownlint issues

remove examples folder

Fixed in d7629bf:

Removed examples/regex-engine folder
Fixed markdown linting issues in docs/guide/regex-engines.md
All markdown lint checks now pass

gaby · 2026-05-05T02:04:19Z

@claude[agent] I'm not sure about the addition of regex.go. It seems like it might be over-engineered.

I believe the approach should be as straightforward as our JSONEncoder and Decoder implementations within the app configuration.

Moved regex types from separate regex.go file into path.go where they are used. This follows the simpler pattern similar to JSONEncoder/Decoder and reduces over-engineering by keeping related code together. Changes: - Removed regex.go and moved RegexEngine/RegexCompiler types to path.go - Moved tests from regex_test.go to path_test.go - All tests pass, no linting issues Agent-Logs-Url: https://github.com/gofiber/fiber/sessions/175129f3-3f03-4a29-9673-b0521797d587 Co-authored-by: gaby <835733+gaby@users.noreply.github.com>

Claude · 2026-05-05T02:10:28Z

@claude[agent] I'm not sure about the addition of regex.go. It seems like it might be over-engineered.

I believe the approach should be as straightforward as our JSONEncoder and Decoder implement...

Simplified in ffc10c3. Removed the separate regex.go file and moved all regex types directly into path.go where they're actually used. This follows a simpler pattern similar to other encoders/decoders and keeps related code together. The abstraction is now more minimal while still providing the flexibility to use alternative regex engines.

gaby · 2026-05-05T02:27:29Z

@claude[agent] Looking at the guide docs/guide/regex-engines.md and code. Using a different regex library is too complicated. We can simplify this.

Following feedback to simplify the regex engine abstraction, this commit refactors the implementation to use a simple function type instead of interface-based approach. Key changes: - Replace RegexEngine interface with RegexHandler function type - RegexHandler is now: func(pattern string) RegexCompiler - Add defaultRegexHandler function that wraps regexp.MustCompile - Update all references from RegexEngine to RegexHandler - Simplify documentation to show direct usage without adapter types This follows the same pattern as JSONEncoder/JSONDecoder in the codebase, making it much simpler for users to adopt alternative regex engines: Before (required adapter types): type CoregexEngine struct{} func (CoregexEngine) MustCompile(pattern string) fiber.RegexCompiler {...} app := fiber.New(fiber.Config{RegexEngine: CoregexEngine{}}) After (just a function): app := fiber.New(fiber.Config{ RegexHandler: func(pattern string) fiber.RegexCompiler { return coregex.MustCompile(pattern) }, }) 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com> Co-authored-by: gaby <835733+gaby@users.noreply.github.com>

gaby · 2026-05-05T04:48:10Z

@claude[agent] Why are you adding a handler, instead of just using coregex.MustCompile. Stdlib and coregex use the same API.

// stdlib
re := regexp.MustCompile(pattern)

// coregex — same API
re := coregex.MustCompile(pattern)

The app config option should just take coregex.MustCompile, i think?

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

gaby · 2026-05-06T02:15:03Z

@copilot apply changes based on the comments in this thread

Agent-Logs-Url: https://github.com/gofiber/fiber/sessions/f9b8dbc7-cc72-4f60-b345-5b668e0ceed6 Co-authored-by: gaby <835733+gaby@users.noreply.github.com>

Copilot · 2026-05-06T02:28:10Z

@copilot apply changes based on the comments in this thread

Applied the review-thread follow-ups in 4d138de. RegexHandler is now validated up front, the matcher contract is reduced to MatchString, failure-mode coverage was added, and the API/guide docs were updated to document the final behavior and concurrency requirement. make lint, make test, and make markdown pass; make audit is still blocked by existing Go 1.25 stdlib govulncheck findings in the environment.

Copilot

Pull request overview

Copilot reviewed 17 out of 17 changed files in this pull request and generated 2 comments.

gaby · 2026-05-06T04:22:43Z

@copilot apply changes based on the comments in this thread

Agent-Logs-Url: https://github.com/gofiber/fiber/sessions/bb345d14-e46f-4eb3-80d3-76fb16369d8d Co-authored-by: gaby <835733+gaby@users.noreply.github.com>

Copilot · 2026-05-06T04:32:14Z

@copilot apply changes based on the comments in this thread

Applied the follow-up changes in 67f902d. RegexHandler now enforces the exact documented func(string) T signature so named-string inputs fail fast, and Constraint.RegexCompiler is back to *regexp.Regexp for compatibility while non-stdlib matchers are stored internally. Targeted regex tests pass, and the full local validation set passes except for the same pre-existing local make audit govulncheck/toolchain findings; the current branch CI workflows are green.

github-actions

⚠️ Performance Alert ⚠️

Possible performance regression was detected for benchmark.
Benchmark result of this commit is worse than the previous benchmark result exceeding threshold 1.50.

Benchmark suite	Current: `67f902d`	Previous: `d5c49b2`	Ratio
`Benchmark_Compress/Zstd (github.com/gofiber/fiber/v3/middleware/compress) - B/op`	`1` B/op	`0` B/op	`+∞`

This comment was automatically generated by workflow using github-action-benchmark.

gaby · 2026-05-21T11:40:08Z

@copilot resolve the merge conflicts in this pull request

…dd-alternative-regex-support # Conflicts: # prefork.go Co-authored-by: gaby <835733+gaby@users.noreply.github.com>

Copilot · 2026-05-21T11:50:16Z

@copilot resolve the merge conflicts in this pull request

Resolved the merge conflict in f9d2dcc by merging main and taking the current prefork.go implementation from main, which was the only conflicted file. Targeted prefork/regex tests passed, make format, make lint, make test, and make markdown passed, and CodeQL found no alerts; make audit still fails locally on the existing Go 1.25 stdlib govulncheck findings, and make modernize still hits the existing Go 1.26 tool requirement from modernize@latest.

Copilot

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 5 comments.

Copilot · 2026-05-21T12:12:03Z

 	case regexConstraint:
-		if c.RegexCompiler == nil {
+		matcher := c.regexMatcher
+		if matcher == nil {
+			matcher = c.RegexCompiler
+		}


Fixed in b131e19. Constraint.CheckConstraint now treats typed-nil regex matchers the same as nil and returns false instead of calling MatchString on a nil receiver.

Copilot · 2026-05-21T12:12:08Z

+// RegexCompiler defines the interface for regex pattern matching.
+// Both *regexp.Regexp and alternative engines like *coregex.Regex implement this method.
+type RegexCompiler interface {
+	// MatchString reports whether the string s contains any match of the regex pattern.
+	MatchString(s string) bool


Fixed in b131e19. I renamed the new interface to RegexMatcher and updated the related validation errors/docs so it no longer clashes with Constraint.RegexCompiler.

Copilot · 2026-05-21T12:12:12Z

+	parsedRaw := parseRoute(pathRaw, app.config.RegexHandler, app.customConstraints...)
+	parsedPretty := parseRoute(pathPretty, app.config.RegexHandler, app.customConstraints...)


Addressed in b131e19 by documenting the current registration behavior. The public config/docs now note that RegexHandler may be invoked more than once per route while Fiber parses raw and normalized patterns.

Copilot · 2026-05-21T12:12:16Z

+// Test_RegexHandler_Default verifies the default regex handler works correctly.
+func Test_RegexHandler_Default(t *testing.T) {
+	t.Parallel()
+
+	require.True(t, regexp.MustCompile(`\d+`).MatchString("123"))
+	require.False(t, regexp.MustCompile(`\d+`).MatchString("abc"))


Fixed in b131e19. I rewrote that test to assert Fiber’s default RegexHandler wiring instead of just re-testing regexp.MustCompile directly.

Copilot · 2026-05-21T12:12:20Z

+
+## Notes
+
+- Regex patterns are compiled once during route registration, so the performance improvement is in the matching phase


Fixed in b131e19. The guide now says regex patterns are compiled during route registration and may be compiled more than once while Fiber parses raw and normalized route patterns.

Agent-Logs-Url: https://github.com/gofiber/fiber/sessions/080c86b4-4942-4e6b-a12f-802358f0c71f Co-authored-by: gaby <835733+gaby@users.noreply.github.com>

Initial plan

57076e1

Claude AI assigned Claude and gaby May 4, 2026

Claude AI linked an issue May 4, 2026 that may be closed by this pull request

📝 [Proposal]: ability to use alternative regex for router #4253

Open

3 tasks

Claude started work on behalf of gaby May 4, 2026 22:40 View session

ReneWerner87 added v3 ✏️ Feature labels May 4, 2026

ReneWerner87 added this to v3 May 4, 2026

ReneWerner87 added this to the v3 milestone May 4, 2026

Claude AI and others added 2 commits May 4, 2026 23:03

Fix linting issues in regex implementation

5bc2ae9

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Claude finished work on behalf of gaby May 4, 2026 23:06

Claude AI requested a review from gaby May 4, 2026 23:06

Claude started work on behalf of gaby May 4, 2026 23:25 View session

Claude finished work on behalf of gaby May 4, 2026 23:29

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Claude finished work on behalf of gaby May 5, 2026 02:11

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Claude finished work on behalf of gaby May 5, 2026 02:40

Potential fix for pull request finding

8a47f89

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Copilot started work on behalf of gaby May 6, 2026 02:15 View session

Copilot AI and others added 3 commits May 6, 2026 02:22

fix: validate and document regex handler config

78bb6f8

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fix: tighten regex handler type assertion

0ae485e

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test: clarify regex handler validation comment

4d138de

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Copilot AI and others added 3 commits May 6, 2026 04:25

fix: preserve regex constraint compatibility

c5d5f75

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chore: align constraint field layout

e9b4907

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refactor: clarify internal regex matcher fallback

67f902d

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Merge remote-tracking branch 'refs/remotes/origin/main' into claude/a…

f9d2dcc

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fix: address regex handler review feedback

b131e19

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Copilot finished work on behalf of gaby May 21, 2026 12:13

		parsedRaw := parseRoute(pathRaw, app.config.RegexHandler, app.customConstraints...)
		parsedPretty := parseRoute(pathPretty, app.config.RegexHandler, app.customConstraints...)


		## Notes

		- Regex patterns are compiled once during route registration, so the performance improvement is in the matching phase

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Claude AI commented May 4, 2026

Alignment with Express API

HTTP RFC Standards Compliance

API Stability

Feature Examples

Checklist:

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