[PRIVACY] Add a DNS method to fetch new updates

- Use TXT records in order to determine the latest available version.
- This addresses a valid privacy issue, as with HTTP requests the server
can keep track(estimated) of how many instances are using Forgejo, with
DNS that's basically not possible as the server will never receive any
data, as the only ones receiving data are DNS resolvers.

(cherry picked from commit 0baefb546a)
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[PRIVACY]: Adjust update checker description

- Resolves #323
- Adjust the description of the update check function on the
installation page to describe the privacy method instead of the HTTP
method by checking gitea.io

(cherry picked from commit 61eae5b105)
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Conflicts:
	modules/updatechecker/update_checker.go
	UpdateRemoteVersion now has a context argument. However, in
	the updated code from Gitea the context comes from the HTTP
	request and does not actually provide any useful context.
	Replace that with context.Background()
(cherry picked from commit ca2200767e)
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custom/conf/app.example.ini

@@ -2202,6 +2202,7 @@ LEVEL = Info
 ;ENABLE_SUCCESS_NOTICE = false
 ;SCHEDULE = @every 168h
 ;HTTP_ENDPOINT = https://dl.gitea.com/gitea/version.json
+;DOMAIN_ENDPOINT = release.forgejo.org
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

modules/updatechecker/update_checker.go

@@ -5,8 +5,11 @@ package updatechecker
 
 import (
 	"context"
+	"errors"
 	"io"
+	"net"
 	"net/http"
+	"strings"
 
 	"code.gitea.io/gitea/modules/json"
 	"code.gitea.io/gitea/modules/proxy"
@@ -27,7 +30,51 @@ func (r *CheckerState) Name() string {
 }
 
 // GiteaUpdateChecker returns error when new version of Gitea is available
-func GiteaUpdateChecker(httpEndpoint string) error {
+func GiteaUpdateChecker(httpEndpoint, domainEndpoint string) error {
+	var version string
+	var err error
+	if domainEndpoint != "" {
+		version, err = getVersionDNS(domainEndpoint)
+	} else {
+		version, err = getVersionHTTP(httpEndpoint)
+	}
+
+	if err != nil {
+		return err
+	}
+
+	return UpdateRemoteVersion(context.Background(), version)
+}
+
+// getVersionDNS will request the TXT records for the domain. If a record starts
+// with "forgejo_versions=" everything after that will be used as the latest
+// version available.
+func getVersionDNS(domainEndpoint string) (version string, err error) {
+	records, err := net.LookupTXT(domainEndpoint)
+	if err != nil {
+		return "", err
+	}
+
+	if len(records) == 0 {
+		return "", errors.New("no TXT records were found")
+	}
+
+	for _, record := range records {
+		if strings.HasPrefix(record, "forgejo_versions=") {
+			// Get all supported versions, separated by a comma.
+			supportedVersions := strings.Split(strings.TrimPrefix(record, "forgejo_versions="), ",")
+			// For now always return the latest supported version.
+			return supportedVersions[len(supportedVersions)-1], nil
+		}
+	}
+
+	return "", errors.New("there is no TXT record with a valid value")
+}
+
+// getVersionHTTP will make an HTTP request to the endpoint, and the returned
+// content is JSON. The "latest.version" path's value will be used as the latest
+// version available.
+func getVersionHTTP(httpEndpoint string) (version string, err error) {
 	httpClient := &http.Client{
 		Transport: &http.Transport{
 			Proxy: proxy.Proxy(),
@@ -36,16 +83,16 @@ func GiteaUpdateChecker(httpEndpoint string) error {
 
 	req, err := http.NewRequest("GET", httpEndpoint, nil)
 	if err != nil {
-		return err
+		return "", err
 	}
 	resp, err := httpClient.Do(req)
 	if err != nil {
-		return err
+		return "", err
 	}
 	defer resp.Body.Close()
 	body, err := io.ReadAll(resp.Body)
 	if err != nil {
-		return err
+		return "", err
 	}
 
 	type respType struct {
@@ -56,10 +103,9 @@ func GiteaUpdateChecker(httpEndpoint string) error {
 	respData := respType{}
 	err = json.Unmarshal(body, &respData)
 	if err != nil {
-		return err
+		return "", err
 	}
-
-	return UpdateRemoteVersion(req.Context(), respData.Latest.Version)
+	return respData.Latest.Version, nil
 }
 
 // UpdateRemoteVersion updates the latest available version of Gitea

modules/updatechecker/update_checker_test.go

@@ -0,0 +1,16 @@
+// Copyright 2023 The Forgejo Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package updatechecker
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDNSUpdate(t *testing.T) {
+	version, err := getVersionDNS("release.forgejo.org")
+	assert.NoError(t, err)
+	assert.NotEmpty(t, version)
+}

options/locale/locale_en-US.ini

@@ -287,6 +287,7 @@ run_user_not_match = The 'run as' username is not the current username: %s -> %s
 internal_token_failed = Failed to generate internal token: %v
 secret_key_failed = Failed to generate secret key: %v
 save_config_failed = Failed to save configuration: %v
+enable_update_checker_helper_forgejo = Periodically checks for new Forgejo versions by checking a DNS TXT record at release.forgejo.org.
 invalid_admin_setting = Administrator account setting is invalid: %v
 invalid_log_root_path = The log path is invalid: %v
 default_keep_email_private = Hide Email Addresses by Default

services/cron/tasks_extended.go

@@ -142,7 +142,8 @@ func registerDeleteOldActions() {
 func registerUpdateGiteaChecker() {
 	type UpdateCheckerConfig struct {
 		BaseConfig
-		HTTPEndpoint string
+		HTTPEndpoint   string
+		DomainEndpoint string
 	}
 	RegisterTaskFatal("update_checker", &UpdateCheckerConfig{
 		BaseConfig: BaseConfig{
@@ -150,10 +151,11 @@ func registerUpdateGiteaChecker() {
 			RunAtStart: false,
 			Schedule:   "@every 168h",
 		},
-		HTTPEndpoint: "https://dl.gitea.com/gitea/version.json",
+		HTTPEndpoint:   "https://dl.gitea.com/gitea/version.json",
+		DomainEndpoint: "release.forgejo.org",
 	}, func(ctx context.Context, _ *user_model.User, config Config) error {
 		updateCheckerConfig := config.(*UpdateCheckerConfig)
-		return updatechecker.GiteaUpdateChecker(updateCheckerConfig.HTTPEndpoint)
+		return updatechecker.GiteaUpdateChecker(updateCheckerConfig.HTTPEndpoint, updateCheckerConfig.DomainEndpoint)
 	})
 }
 

templates/install.tmpl

@@ -152,7 +152,7 @@
 							<label>{{ctx.Locale.Tr "install.enable_update_checker"}}</label>
 							<input name="enable_update_checker" type="checkbox">
 						</div>
-						<span class="help">{{ctx.Locale.Tr "install.enable_update_checker_helper"}}</span>
+						<span class="help">{{ctx.Locale.Tr "install.enable_update_checker_helper_forgejo"}}</span>
 					</div>
 
 					<!-- Optional Settings -->