feat: Support adding a proxy server in between when forwarding requests to upstream (#2710)

Co-authored-by: 澄潭 <zty98751@alibaba-inc.com>

pkg/common/proxy.go

@@ -0,0 +1,59 @@
+// Copyright (c) 2022 Alibaba Group Holding Ltd.
+//
+// Licensed 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 common
+
+import (
+	"strings"
+)
+
+type ProxyType string
+
+const (
+	ProxyType_Unknown ProxyType = "Unknown"
+	ProxyType_HTTP    ProxyType = "HTTP"
+	ProxyType_HTTPS   ProxyType = "HTTPS"
+	ProxyType_SOCKS4  ProxyType = "SOCKS4"
+	ProxyType_SOCKS5  ProxyType = "SOCKS5"
+)
+
+func ParseProxyType(s string) ProxyType {
+	switch strings.ToLower(s) {
+	case "http":
+		return ProxyType_HTTP
+	case "https":
+		return ProxyType_HTTPS
+	case "socks4":
+		return ProxyType_SOCKS4
+	case "socks5":
+		return ProxyType_SOCKS5
+	}
+	return ProxyType_Unknown
+}
+
+func (p ProxyType) GetTransportProtocol() Protocol {
+	switch p {
+	case ProxyType_HTTP:
+		return HTTP
+	case ProxyType_HTTPS:
+		return HTTPS
+	case ProxyType_SOCKS4, ProxyType_SOCKS5:
+		return TCP
+	}
+	return Unsupported
+}
+
+func (p ProxyType) String() string {
+	return string(p)
+}