fix: address PR review for replacer — nil check, EscapedPath, scheme reuse, perf

- add req.URL nil guard
- use EscapedPath for {path} to avoid illegal header characters
- reuse reverseProxyRequestScheme for {scheme} consistency
- replace strings.NewReplacer with struct fields + strings.ReplaceAll

reverseproxy.go

@@ -264,32 +264,26 @@ func (ops *HeaderOps) Provision() error {
 }
 
 type reverseProxyReplacer struct {
-	req    *http.Request
-	repl   *strings.Replacer
+	method, host, path, query, scheme, uri, proto string
 }
 
 func newReverseProxyReplacer(req *http.Request) *reverseProxyReplacer {
-	r := &reverseProxyReplacer{req: req}
-	if req != nil {
-		uri := req.RequestURI
-		if uri == "" {
-			uri = req.URL.RequestURI()
-		}
-		scheme := "http"
-		if req.TLS != nil {
-			scheme = "https"
-		}
-		r.repl = strings.NewReplacer(
-			"{method}", req.Method,
-			"{host}", req.Host,
-			"{path}", req.URL.Path,
-			"{query}", req.URL.RawQuery,
-			"{scheme}", scheme,
-			"{uri}", uri,
-			"{proto}", req.Proto,
-		)
+	if req == nil || req.URL == nil {
+		return &reverseProxyReplacer{}
+	}
+	uri := req.RequestURI
+	if uri == "" {
+		uri = req.URL.RequestURI()
+	}
+	return &reverseProxyReplacer{
+		method: req.Method,
+		host:   req.Host,
+		path:   req.URL.EscapedPath(),
+		query:  req.URL.RawQuery,
+		scheme: reverseProxyRequestScheme(req),
+		uri:    uri,
+		proto:  req.Proto,
 	}
-	return r
 }
 
 func newReverseProxyReplacerFromHeader(hdr http.Header) *reverseProxyReplacer {
@@ -300,10 +294,28 @@ func (r *reverseProxyReplacer) Replace(s string) string {
 	if r == nil || s == "" {
 		return s
 	}
-	if r.repl == nil {
-		return s
+	if r.method != "" {
+		s = strings.ReplaceAll(s, "{method}", r.method)
 	}
-	return r.repl.Replace(s)
+	if r.host != "" {
+		s = strings.ReplaceAll(s, "{host}", r.host)
+	}
+	if r.path != "" {
+		s = strings.ReplaceAll(s, "{path}", r.path)
+	}
+	if r.query != "" {
+		s = strings.ReplaceAll(s, "{query}", r.query)
+	}
+	if r.scheme != "" {
+		s = strings.ReplaceAll(s, "{scheme}", r.scheme)
+	}
+	if r.uri != "" {
+		s = strings.ReplaceAll(s, "{uri}", r.uri)
+	}
+	if r.proto != "" {
+		s = strings.ReplaceAll(s, "{proto}", r.proto)
+	}
+	return s
 }
 
 type reverseProxyHandler struct {