refactor(sarin): extract cookie header building into cookieHeaderValue

internal/sarin/request.go

@@ -191,8 +191,18 @@ func applyRequestDataToFastHTTP(reqData *script.RequestData, req *fasthttp.Reque
 	}
 
 	if len(reqData.Cookies) > 0 {
+		req.Header.Add("Cookie", cookieHeaderValue(reqData.Cookies))
+	}
+
+	if scheme == "https" {
+		req.URI().SetScheme("https")
+	}
+}
+
+// cookieHeaderValue joins cookies into a single Cookie header value ("a=1; b=2").
+func cookieHeaderValue(cookies map[string][]string) string {
 	var sb strings.Builder
-		for k, values := range reqData.Cookies {
+	for k, values := range cookies {
 		for _, v := range values {
 			if sb.Len() > 0 {
 				sb.WriteString("; ")
@@ -202,12 +212,7 @@ func applyRequestDataToFastHTTP(reqData *script.RequestData, req *fasthttp.Reque
 			sb.WriteString(v)
 		}
 	}
-		req.Header.Add("Cookie", sb.String())
-	}
-
-	if scheme == "https" {
-		req.URI().SetScheme("https")
-	}
+	return sb.String()
 }
 
 func NewMethodGeneratorFunc(localRand *rand.Rand, methods []string, lazyRoot func() *template.Template) (requestDataGenerator, bool) {