From 0d1ade4626e627ea9737ed7a3659dccd0204b38a Mon Sep 17 00:00:00 2001
From: Kashiwa <13825170+ksw2000@users.noreply.github.com>
Date: Mon, 24 Feb 2025 15:13:47 +0800
Subject: [PATCH] =?UTF-8?q?=E2=99=BB=EF=B8=8F=20Refactor:=20Improve=20Perf?=
 =?UTF-8?q?ormance=20of=20getSplicedStrList=20(#3318)?=
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* ♻️ Refactor: improve performance of getSplicedStrList

goos: linux
goarch: amd64
pkg: github.com/gofiber/fiber/v3
cpu: AMD EPYC 7763 64-Core Processor
                           │   old.txt   │               new.txt               │
                           │   sec/op    │   sec/op     vs base                │
_Utils_GetSplicedStrList-4   66.12n ± 1%   51.05n ± 1%  -22.79% (p=0.000 n=50)

                           │  old.txt   │            new.txt             │
                           │    B/op    │    B/op     vs base            │
_Utils_GetSplicedStrList-4   0.000 ± 0%   0.000 ± 0%  ~ (p=1.000 n=50) ¹
¹ all samples are equal

                           │  old.txt   │            new.txt             │
                           │ allocs/op  │ allocs/op   vs base            │
_Utils_GetSplicedStrList-4   0.000 ± 0%   0.000 ± 0%  ~ (p=1.000 n=50) ¹
¹ all samples are equal

* 🚨 Test: add more test for getSplicedStrList

* 🩹 Fix: golangci-lint ifElseChain

* ♻️ Refactor: use more descriptive variable names
---
 helpers.go      | 33 ++++++++++++++-------------------
 helpers_test.go | 20 ++++++++++++++++++++
 2 files changed, 34 insertions(+), 19 deletions(-)

diff --git a/helpers.go b/helpers.go
index eea6b370..18728e56 100644
--- a/helpers.go
+++ b/helpers.go
@@ -321,28 +321,23 @@ func getSplicedStrList(headerValue string, dst []string) []string {
 		return nil
 	}
 
-	var (
-		index             int
-		character         rune
-		lastElementEndsAt int
-		insertIndex       int
-	)
-	for index, character = range headerValue + "$" {
-		if character == ',' || index == len(headerValue) {
-			if insertIndex >= len(dst) {
-				oldSlice := dst
-				dst = make([]string, len(dst)+(len(dst)>>1)+2)
-				copy(dst, oldSlice)
-			}
-			dst[insertIndex] = utils.TrimLeft(headerValue[lastElementEndsAt:index], ' ')
-			lastElementEndsAt = index + 1
-			insertIndex++
+	dst = dst[:0]
+	segmentStart := 0
+	isLeadingSpace := true
+	for i, c := range headerValue {
+		switch {
+		case c == ',':
+			dst = append(dst, headerValue[segmentStart:i])
+			segmentStart = i + 1
+			isLeadingSpace = true
+		case c == ' ' && isLeadingSpace:
+			segmentStart = i + 1
+		default:
+			isLeadingSpace = false
 		}
 	}
+	dst = append(dst, headerValue[segmentStart:])
 
-	if len(dst) > insertIndex {
-		dst = dst[:insertIndex]
-	}
 	return dst
 }
 
diff --git a/helpers_test.go b/helpers_test.go
index 75698d87..5664bc48 100644
--- a/helpers_test.go
+++ b/helpers_test.go
@@ -303,6 +303,26 @@ func Test_Utils_GetSplicedStrList(t *testing.T) {
 			headerValue:  "gzip,",
 			expectedList: []string{"gzip", ""},
 		},
+		{
+			description:  "has a space between words",
+			headerValue:  "  foo bar, hello  world",
+			expectedList: []string{"foo bar", "hello  world"},
+		},
+		{
+			description:  "single comma",
+			headerValue:  ",",
+			expectedList: []string{"", ""},
+		},
+		{
+			description:  "multiple comma",
+			headerValue:  ",,",
+			expectedList: []string{"", "", ""},
+		},
+		{
+			description:  "comma with space",
+			headerValue:  ",  ,",
+			expectedList: []string{"", "", ""},
+		},
 	}
 
 	for _, tc := range testCases {