⚡ middleware/pprof: improve performance

[database64128]

Description

Concatenate the custom and fixed prefixes beforehand, so the trimmed path can be switched on against constant strings.

Here's a simple benchmark:

package pprof

import (
	"crypto/rand"
	"errors"
	"strings"
	"testing"
	"unsafe"
)

var errBadPath = errors.New("bad path")

func doSlow(prefix, path string) error {
	if len(path) < 12 || !strings.HasPrefix(path, prefix+"/debug/pprof") {
		return errBadPath
	}
	// Switch to original path without stripped slashes
	switch path {
	case prefix + "/debug/pprof/":
		return errBadPath
	case prefix + "/debug/pprof/cmdline":
		return errBadPath
	case prefix + "/debug/pprof/profile":
		return errBadPath
	case prefix + "/debug/pprof/symbol":
		return errBadPath
	case prefix + "/debug/pprof/trace":
		return errBadPath
	case prefix + "/debug/pprof/allocs":
		return errBadPath
	case prefix + "/debug/pprof/block":
		return errBadPath
	case prefix + "/debug/pprof/goroutine":
		return errBadPath
	case prefix + "/debug/pprof/heap":
		return errBadPath
	case prefix + "/debug/pprof/mutex":
		return errBadPath
	case prefix + "/debug/pprof/threadcreate":
		return errBadPath
	default:
		return nil
	}
}

func newSlowBenchFunc(prefix, path string) func(b *testing.B) {
	return func(b *testing.B) {
		for i := 0; i < b.N; i++ {
			if err := doSlow(prefix, path); err != nil {
				b.Error(err)
			}
		}
	}
}

func doFast(prefix, path string) error {
	path, found := strings.CutPrefix(path, prefix)
	if !found {
		return errBadPath
	}
	// Switch to original path without stripped slashes
	switch path {
	case "", "/":
		return errBadPath
	case "/cmdline":
		return errBadPath
	case "/profile":
		return errBadPath
	case "/symbol":
		return errBadPath
	case "/trace":
		return errBadPath
	case "/allocs":
		return errBadPath
	case "/block":
		return errBadPath
	case "/goroutine":
		return errBadPath
	case "/heap":
		return errBadPath
	case "/mutex":
		return errBadPath
	case "/threadcreate":
		return errBadPath
	default:
		return nil
	}

}

func newFastBenchFunc(prefix, path string) func(b *testing.B) {
	prefix += "/debug/pprof"
	return func(b *testing.B) {
		for i := 0; i < b.N; i++ {
			if err := doFast(prefix, path); err != nil {
				b.Error(err)
			}
		}
	}
}

func BenchmarkPprof(b *testing.B) {
	buf := make([]byte, 16)
	if _, err := rand.Read(buf); err != nil {
		b.Fatal(err)
	}
	prefix := unsafe.String(unsafe.SliceData(buf), len(buf))
	path := prefix + "/debug/pprof/nonexistent"

	b.Run("Slow", newSlowBenchFunc(prefix, path))
	b.Run("Fast", newFastBenchFunc(prefix, path))
}

goos: linux
goarch: amd64
pkg: github.com/gofiber/fiber/v2/middleware/pprof
cpu: 13th Gen Intel(R) Core(TM) i9-13900K
BenchmarkPprof/Slow-32         	 4912642	       246.3 ns/op	     480 B/op	      10 allocs/op
BenchmarkPprof/Fast-32         	411908472	         2.913 ns/op	       0 B/op	       0 allocs/op
PASS

To the maintainers: These slow patterns introduced by #2194 were quite obvious, and it would've been nice if they were called out when the PR was being reviewed. Thanks!

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• For new functionalities I follow the inspiration of the express js framework and built them similar in usage
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation - /docs/ directory for https://docs.gofiber.io/
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• If new dependencies exist, I have checked that they are really necessary and agreed with the maintainers/community (we want to have as few dependencies as possible)
• I tried to make my code as fast as possible with as few allocations as possible
• For new code I have written benchmarks so that they can be analyzed and improved

Commit formatting:

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[welcome]

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[efectn]

Nice catch

[gaby]

LGTM!

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