perf: use more efficient removeRepeatedChar for path slash handling

gin.go

@@ -13,7 +13,6 @@ import (
 	"path"
 	"strings"
 	"sync"
-	"unicode"
 
 	"github.com/gin-gonic/gin/internal/bytesconv"
 	filesystem "github.com/gin-gonic/gin/internal/fs"
@@ -772,7 +771,7 @@ func redirectTrailingSlash(c *Context) {
 	p := req.URL.Path
 	if prefix := path.Clean(c.Request.Header.Get("X-Forwarded-Prefix")); prefix != "." {
 		prefix = sanitizePathChars(prefix)
-		prefix = removeRepeatedSlash(prefix)
+		prefix = removeRepeatedChar(prefix, '/')
 
 		p = prefix + "/" + req.URL.Path
 	}
@@ -784,38 +783,16 @@ func redirectTrailingSlash(c *Context) {
 }
 
 // sanitizePathChars removes unsafe characters from path strings,
-// keeping only letters, numbers, forward slashes, and hyphens.
+// keeping only ASCII letters, ASCII numbers, forward slashes, and hyphens.
 func sanitizePathChars(s string) string {
 	return strings.Map(func(r rune) rune {
-		if unicode.IsLetter(r) || unicode.IsDigit(r) || r == '/' || r == '-' {
+		if (r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z') || (r >= '0' && r <= '9') || r == '/' || r == '-' {
 			return r
 		}
 		return -1
 	}, s)
 }
 
-// removeRepeatedSlash removes consecutive forward slashes from a string,
-// replacing sequences of multiple slashes with a single slash.
-func removeRepeatedSlash(s string) string {
-	if !strings.Contains(s, "//") {
-		return s
-	}
-
-	var sb strings.Builder
-	sb.Grow(len(s) - 1)
-	prevChar := rune(0)
-
-	for _, r := range s {
-		if r == '/' && prevChar == '/' {
-			continue
-		}
-		sb.WriteRune(r)
-		prevChar = r
-	}
-
-	return sb.String()
-}
-
 func redirectFixedPath(c *Context, root *node, trailingSlash bool) bool {
 	req := c.Request
 	rPath := req.URL.Path

gin_test.go

@@ -1012,34 +1012,3 @@ func TestUpdateRouteTreesCalledOnce(t *testing.T) {
 		assert.Equal(t, "ok", w.Body.String())
 	}
 }
-
-func TestRemoveRepeatedSlash(t *testing.T) {
-	testCases := []struct {
-		name string
-		str  string
-		want string
-	}{
-		{
-			name: "noSlash",
-			str:  "abc",
-			want: "abc",
-		},
-		{
-			name: "withSlash",
-			str:  "/a/b/c/",
-			want: "/a/b/c/",
-		},
-		{
-			name: "withRepeatedSlash",
-			str:  "/a//b///c////",
-			want: "/a/b/c/",
-		},
-	}
-
-	for _, tc := range testCases {
-		t.Run(tc.name, func(t *testing.T) {
-			res := removeRepeatedSlash(tc.str)
-			assert.Equal(t, tc.want, res)
-		})
-	}
-}

path.go

@@ -5,6 +5,8 @@
 
 package gin
 
+const stackBufSize = 128
+
 // cleanPath is the URL version of path.Clean, it returns a canonical URL path
 // for p, eliminating . and .. elements.
 //
@@ -19,7 +21,6 @@ package gin
 //
 // If the result of this process is an empty string, "/" is returned.
 func cleanPath(p string) string {
-	const stackBufSize = 128
 	// Turn empty string into "/"
 	if p == "" {
 		return "/"
@@ -148,3 +149,55 @@ func bufApp(buf *[]byte, s string, w int, c byte) {
 	}
 	b[w] = c
 }
+
+// removeRepeatedChar removes multiple consecutive 'char's from a string.
+// if s == "/a//b///c////" && char == '/', it returns "/a/b/c/"
+func removeRepeatedChar(s string, char byte) string {
+	// Check if there are any consecutive chars
+	hasRepeatedChar := false
+	for i := 1; i < len(s); i++ {
+		if s[i] == char && s[i-1] == char {
+			hasRepeatedChar = true
+			break
+		}
+	}
+	if !hasRepeatedChar {
+		return s
+	}
+
+	// Reasonably sized buffer on stack to avoid allocations in the common case.
+	buf := make([]byte, 0, stackBufSize)
+
+	// Invariants:
+	//      reading from s; r is index of next byte to process.
+	//      writing to buf; w is index of next byte to write.
+	r := 0
+	w := 0
+
+	for n := len(s); r < n; {
+		if s[r] == char {
+			// Write the first char
+			bufApp(&buf, s, w, char)
+			w++
+			r++
+
+			// Skip all consecutive chars
+			for r < n && s[r] == char {
+				r++
+			}
+		} else {
+			// Copy non-char character
+			bufApp(&buf, s, w, s[r])
+			w++
+			r++
+		}
+	}
+
+	// If the original string was not modified (or only shortened at the end),
+	// return the respective substring of the original string.
+	// Otherwise, return a new string from the buffer.
+	if len(buf) == 0 {
+		return s[:w]
+	}
+	return string(buf[:w])
+}

path_test.go

@@ -143,3 +143,50 @@ func BenchmarkPathCleanLong(b *testing.B) {
 		}
 	}
 }
+
+func TestRemoveRepeatedChar(t *testing.T) {
+	testCases := []struct {
+		name string
+		str  string
+		char byte
+		want string
+	}{
+		{
+			name: "empty",
+			str:  "",
+			char: 'a',
+			want: "",
+		},
+		{
+			name: "noSlash",
+			str:  "abc",
+			char: ',',
+			want: "abc",
+		},
+		{
+			name: "withSlash",
+			str:  "/a/b/c/",
+			char: '/',
+			want: "/a/b/c/",
+		},
+		{
+			name: "withRepeatedSlashes",
+			str:  "/a//b///c////",
+			char: '/',
+			want: "/a/b/c/",
+		},
+		{
+			name: "threeSlashes",
+			str:  "///",
+			char: '/',
+			want: "/",
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			res := removeRepeatedChar(tc.str, tc.char)
+			assert.Equal(t, tc.want, res)
+		})
+	}
+}