Add proxy settings and support for migration and webhook (#16704)

* Add proxy settings and support for migration and webhook

* Fix default value

* Add newline for example ini

* Add lfs proxy support

* Fix lint

* Follow @zeripath's review

* Fix git clone

* Fix test

* missgin http requests for proxy

* use empty

Co-authored-by: zeripath <art27@cantab.net>

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: zeripath <art27@cantab.net>

modules/proxy/proxy.go

@@ -0,0 +1,83 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package proxy
+
+import (
+	"net/http"
+	"net/url"
+	"os"
+	"sync"
+
+	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/setting"
+
+	"github.com/gobwas/glob"
+)
+
+var (
+	once         sync.Once
+	hostMatchers []glob.Glob
+)
+
+// GetProxyURL returns proxy url
+func GetProxyURL() string {
+	if !setting.Proxy.Enabled {
+		return ""
+	}
+
+	if setting.Proxy.ProxyURL == "" {
+		if os.Getenv("http_proxy") != "" {
+			return os.Getenv("http_proxy")
+		}
+		return os.Getenv("https_proxy")
+	}
+	return setting.Proxy.ProxyURL
+}
+
+// Match return true if url needs to be proxied
+func Match(u string) bool {
+	if !setting.Proxy.Enabled {
+		return false
+	}
+
+	// enforce do once
+	Proxy()
+
+	for _, v := range hostMatchers {
+		if v.Match(u) {
+			return true
+		}
+	}
+	return false
+}
+
+// Proxy returns the system proxy
+func Proxy() func(req *http.Request) (*url.URL, error) {
+	if !setting.Proxy.Enabled {
+		return nil
+	}
+	if setting.Proxy.ProxyURL == "" {
+		return http.ProxyFromEnvironment
+	}
+
+	once.Do(func() {
+		for _, h := range setting.Proxy.ProxyHosts {
+			if g, err := glob.Compile(h); err == nil {
+				hostMatchers = append(hostMatchers, g)
+			} else {
+				log.Error("glob.Compile %s failed: %v", h, err)
+			}
+		}
+	})
+
+	return func(req *http.Request) (*url.URL, error) {
+		for _, v := range hostMatchers {
+			if v.Match(req.URL.Host) {
+				return http.ProxyURL(setting.Proxy.ProxyURLFixed)(req)
+			}
+		}
+		return http.ProxyFromEnvironment(req)
+	}
+}