chore: import upstream snapshot with attribution

pkg/checker/url.go

@@ -0,0 +1,43 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package checker
+
+import (
+	"net/url"
+	"strings"
+)
+
+func IsURL(str string) bool {
+	s := strings.ToLower(str)
+
+	if len(s) == 0 {
+		return false
+	}
+
+	u, err := url.Parse(s)
+	if err != nil || u.Scheme == "" {
+		return false
+	}
+
+	if u.Host == "" && u.Fragment == "" && u.Opaque == "" {
+		return false
+	}
+	return u.Scheme == "http" || u.Scheme == "https"
+}