From bd66659ec11993feb44f6217eb7d1bf762fd4875 Mon Sep 17 00:00:00 2001
From: Tit Petric <tit@tyk.io>
Date: Thu, 24 Aug 2023 14:53:00 +0200
Subject: [PATCH] Optimize allocations in newRouteRegexp

---
 regexp.go | 53 +++++++++++++++++++++++++++++++++++++----------------
 1 file changed, 37 insertions(+), 16 deletions(-)

diff --git a/regexp.go b/regexp.go
index 0baba6a4..4c916c8b 100644
--- a/regexp.go
+++ b/regexp.go
@@ -65,35 +65,48 @@ func newRouteRegexp(tpl string, typ regexpType, options routeRegexpOptions) (*ro
 	}
 	varsN := make([]string, len(idxs)/2)
 	varsR := make([]*regexp.Regexp, len(idxs)/2)
-	pattern := bytes.NewBufferString("")
+
+	var pattern, reverse strings.Builder
 	pattern.WriteByte('^')
-	reverse := bytes.NewBufferString("")
-	var end int
+
+	var end, colonIdx, groupIdx int
 	var err error
+	var patt, param, name string
 	for i := 0; i < len(idxs); i += 2 {
 		// Set all values we are interested in.
+		groupIdx = i/2
+
 		raw := tpl[end:idxs[i]]
 		end = idxs[i+1]
-		parts := strings.SplitN(tpl[idxs[i]+1:end-1], ":", 2)
-		name := parts[0]
-		patt := defaultPattern
-		if len(parts) == 2 {
-			patt = parts[1]
+
+		param = tpl[idxs[i]+1 : end-1]
+		colonIdx = strings.Index(param, ":")
+		if colonIdx == -1 {
+			name = param
+			patt = defaultPattern
+		} else {
+			name = param[0:colonIdx]
+			patt = param[colonIdx+1:]
+		}
+		if patt == "" {
+			patt = defaultPattern
 		}
+
 		// Name or pattern can't be empty.
 		if name == "" || patt == "" {
-			return nil, fmt.Errorf("mux: missing name or pattern in %q",
-				tpl[idxs[i]:end])
+			return nil, fmt.Errorf("mux: missing name or pattern in %q", param)
 		}
 		// Build the regexp pattern.
-		fmt.Fprintf(pattern, "%s(?P<%s>%s)", regexp.QuoteMeta(raw), varGroupName(i/2), patt)
+		groupName := varGroupName(groupIdx)
+
+		pattern.WriteString(regexp.QuoteMeta(raw)+"(?P<" + groupName + ">" + patt + ")")
 
 		// Build the reverse template.
-		fmt.Fprintf(reverse, "%s%%s", raw)
+		reverse.WriteString(raw+"%s")
 
 		// Append variable name and compiled pattern.
-		varsN[i/2] = name
-		varsR[i/2], err = RegexpCompileFunc(fmt.Sprintf("^%s$", patt))
+		varsN[groupIdx] = name
+		varsR[groupIdx], err = RegexpCompileFunc("^" + patt + "$")
 		if err != nil {
 			return nil, err
 		}
@@ -101,31 +114,39 @@ func newRouteRegexp(tpl string, typ regexpType, options routeRegexpOptions) (*ro
 	// Add the remaining.
 	raw := tpl[end:]
 	pattern.WriteString(regexp.QuoteMeta(raw))
+
 	if options.strictSlash {
 		pattern.WriteString("[/]?")
 	}
+
 	if typ == regexpTypeQuery {
 		// Add the default pattern if the query value is empty
 		if queryVal := strings.SplitN(template, "=", 2)[1]; queryVal == "" {
 			pattern.WriteString(defaultPattern)
 		}
 	}
+
 	if typ != regexpTypePrefix {
 		pattern.WriteByte('$')
 	}
 
+	patternStr := pattern.String()
+
 	var wildcardHostPort bool
 	if typ == regexpTypeHost {
-		if !strings.Contains(pattern.String(), ":") {
+		if !strings.Contains(patternStr, ":") {
 			wildcardHostPort = true
 		}
 	}
+
 	reverse.WriteString(raw)
+
 	if endSlash {
 		reverse.WriteByte('/')
 	}
+
 	// Compile full regexp.
-	reg, errCompile := RegexpCompileFunc(pattern.String())
+	reg, errCompile := RegexpCompileFunc(patternStr)
 	if errCompile != nil {
 		return nil, errCompile
 	}