Add simple update checker to Gitea (#17212)

* Add simple update checker to Gitea

* update struct and remove comments

* fix lint

* Update custom/conf/app.example.ini

* Update docs/content/doc/advanced/config-cheat-sheet.en-us.md

Co-authored-by: delvh <dev.lh@web.de>

* Update custom/conf/app.example.ini

Co-authored-by: delvh <dev.lh@web.de>

* Update docs/content/doc/advanced/config-cheat-sheet.en-us.md

Co-authored-by: delvh <dev.lh@web.de>

* Update docs/content/doc/advanced/config-cheat-sheet.en-us.md

Co-authored-by: Steven <61625851+justusbunsi@users.noreply.github.com>

* Update docs/content/doc/advanced/config-cheat-sheet.en-us.md

* Update modules/cron/tasks_extended.go

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

* Update custom/conf/app.example.ini

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

* take PR feedback into account and display banner on admin dashboard for alerts

* Add more detailed message

* placate lint

* update per feedback

Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: Steven <61625851+justusbunsi@users.noreply.github.com>
Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

models/update_checker.go

@@ -0,0 +1,121 @@
+// 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 models
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+
+	"code.gitea.io/gitea/models/db"
+	"code.gitea.io/gitea/modules/proxy"
+	"code.gitea.io/gitea/modules/setting"
+
+	"github.com/hashicorp/go-version"
+)
+
+// RemoteVersion stores the remote version from the JSON endpoint
+type RemoteVersion struct {
+	ID      int64  `xorm:"pk autoincr"`
+	Version string `xorm:"VARCHAR(50)"`
+}
+
+func init() {
+	db.RegisterModel(new(RemoteVersion))
+}
+
+// GiteaUpdateChecker returns error when new version of Gitea is available
+func GiteaUpdateChecker(httpEndpoint string) error {
+	httpClient := &http.Client{
+		Transport: &http.Transport{
+			Proxy: proxy.Proxy(),
+		},
+	}
+
+	req, err := http.NewRequest("GET", httpEndpoint, nil)
+	if err != nil {
+		return err
+	}
+	resp, err := httpClient.Do(req)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+	body, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		return err
+	}
+
+	type v struct {
+		Latest struct {
+			Version string `json:"version"`
+		} `json:"latest"`
+	}
+	ver := v{}
+	err = json.Unmarshal(body, &ver)
+	if err != nil {
+		return err
+	}
+
+	return UpdateRemoteVersion(ver.Latest.Version)
+
+}
+
+// UpdateRemoteVersion updates the latest available version of Gitea
+func UpdateRemoteVersion(version string) (err error) {
+	sess := db.NewSession(db.DefaultContext)
+	defer sess.Close()
+	if err = sess.Begin(); err != nil {
+		return err
+	}
+
+	currentVersion := &RemoteVersion{ID: 1}
+	has, err := sess.Get(currentVersion)
+	if err != nil {
+		return fmt.Errorf("get: %v", err)
+	} else if !has {
+		currentVersion.ID = 1
+		currentVersion.Version = version
+
+		if _, err = sess.InsertOne(currentVersion); err != nil {
+			return fmt.Errorf("insert: %v", err)
+		}
+		return nil
+	}
+
+	if _, err = sess.Update(&RemoteVersion{ID: 1, Version: version}); err != nil {
+		return err
+	}
+
+	return sess.Commit()
+}
+
+// GetRemoteVersion returns the current remote version (or currently installed verson if fail to fetch from DB)
+func GetRemoteVersion() string {
+	e := db.GetEngine(db.DefaultContext)
+	v := &RemoteVersion{ID: 1}
+	_, err := e.Get(&v)
+	if err != nil {
+		// return current version if fail to fetch from DB
+		return setting.AppVer
+	}
+	return v.Version
+}
+
+// GetNeedUpdate returns true whether a newer version of Gitea is available
+func GetNeedUpdate() bool {
+	curVer, err := version.NewVersion(setting.AppVer)
+	if err != nil {
+		// return false to fail silently
+		return false
+	}
+	remoteVer, err := version.NewVersion(GetRemoteVersion())
+	if err != nil {
+		// return false to fail silently
+		return false
+	}
+	return curVer.LessThan(remoteVer)
+}