2 files changed, 160 insertions, 0 deletions
diff --git a/modules/updatechecker/update_checker.go b/modules/updatechecker/update_checker.go
new file mode 100644
index 00000000..0c93f08d
--- /dev/null
+++ b/modules/updatechecker/update_checker.go
@@ -0,0 +1,143 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package updatechecker
+
+import (
+	"context"
+	"errors"
+	"io"
+	"net"
+	"net/http"
+	"strings"
+
+	"code.gitea.io/gitea/modules/json"
+	"code.gitea.io/gitea/modules/proxy"
+	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/system"
+
+	"github.com/hashicorp/go-version"
+)
+
+// CheckerState stores the remote version from the JSON endpoint
+type CheckerState struct {
+	LatestVersion string
+}
+
+// Name returns the name of the state item for update checker
+func (r *CheckerState) Name() string {
+	return "update-checker"
+}
+
+// GiteaUpdateChecker returns error when new version of Gitea is available
+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(),
+		},
+	}
+
+	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 := io.ReadAll(resp.Body)
+	if err != nil {
+		return "", err
+	}
+
+	type respType struct {
+		Latest struct {
+			Version string `json:"version"`
+		} `json:"latest"`
+	}
+	respData := respType{}
+	err = json.Unmarshal(body, &respData)
+	if err != nil {
+		return "", err
+	}
+	return respData.Latest.Version, nil
+}
+
+// UpdateRemoteVersion updates the latest available version of Gitea
+func UpdateRemoteVersion(ctx context.Context, version string) (err error) {
+	return system.AppState.Set(ctx, &CheckerState{LatestVersion: version})
+}
+
+// GetRemoteVersion returns the current remote version (or currently installed version if fail to fetch from DB)
+func GetRemoteVersion(ctx context.Context) string {
+	item := new(CheckerState)
+	if err := system.AppState.Get(ctx, item); err != nil {
+		return ""
+	}
+	return item.LatestVersion
+}
+
+// GetNeedUpdate returns true whether a newer version of Gitea is available
+func GetNeedUpdate(ctx context.Context) bool {
+	curVer, err := version.NewVersion(setting.AppVer)
+	if err != nil {
+		// return false to fail silently
+		return false
+	}
+	remoteVerStr := GetRemoteVersion(ctx)
+	if remoteVerStr == "" {
+		// no remote version is known
+		return false
+	}
+	remoteVer, err := version.NewVersion(remoteVerStr)
+	if err != nil {
+		// return false to fail silently
+		return false
+	}
+	return curVer.LessThan(remoteVer)
+}
diff --git a/modules/updatechecker/update_checker_test.go b/modules/updatechecker/update_checker_test.go
new file mode 100644
index 00000000..5ac2603c
--- /dev/null
+++ b/modules/updatechecker/update_checker_test.go
@@ -0,0 +1,17 @@
+// Copyright 2023 The Forgejo Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package updatechecker
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestDNSUpdate(t *testing.T) {
+	version, err := getVersionDNS("release.forgejo.org")
+	require.NoError(t, err)
+	assert.NotEmpty(t, version)
+}