Pull request: 2546 updater fix

Merge in DNS/adguard-home from 2546-updater-fix to master

Closes #2546.

Squashed commit of the following:

commit af243c9fad710efe099506fda281e628c3e5ec30
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed Jan 13 14:33:37 2021 +0300

    updater: fix go 1.14 compat

commit 742fba24b300ce51c04acb586996c3c75e56ea20
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed Jan 13 13:58:27 2021 +0300

    util: imp error check

commit c2bdbce8af657a7f4b7e05c018cfacba86e06753
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Mon Jan 11 18:51:26 2021 +0300

    all: fix and refactor update checking

internal/updater/check.go

@@ -0,0 +1,117 @@
+package updater
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"strings"
+	"time"
+
+	"github.com/AdguardTeam/AdGuardHome/internal/aghio"
+)
+
+// TODO(a.garipov): Make configurable.
+const versionCheckPeriod = 8 * time.Hour
+
+// VersionInfo contains information about a new version.
+type VersionInfo struct {
+	NewVersion           string
+	Announcement         string
+	AnnouncementURL      string
+	SelfUpdateMinVersion string
+	CanAutoUpdate        bool
+}
+
+// MaxResponseSize is responses on server's requests maximum length in bytes.
+const MaxResponseSize = 64 * 1024
+
+// VersionInfo downloads the latest version information.  If forceRecheck is
+// false and there are cached results, those results are returned.
+func (u *Updater) VersionInfo(forceRecheck bool) (VersionInfo, error) {
+	u.mu.Lock()
+	defer u.mu.Unlock()
+
+	now := time.Now()
+	recheckTime := u.prevCheckTime.Add(versionCheckPeriod)
+	if !forceRecheck && now.Before(recheckTime) {
+		return u.prevCheckResult, u.prevCheckError
+	}
+
+	vcu := u.versionCheckURL
+	resp, err := u.client.Get(vcu)
+	if err != nil {
+		return VersionInfo{}, fmt.Errorf("updater: HTTP GET %s: %w", vcu, err)
+	}
+	defer resp.Body.Close()
+
+	resp.Body, err = aghio.LimitReadCloser(resp.Body, MaxResponseSize)
+	if err != nil {
+		return VersionInfo{}, fmt.Errorf("updater: LimitReadCloser: %w", err)
+	}
+	defer resp.Body.Close()
+
+	// This use of ReadAll is safe, because we just limited the appropriate
+	// ReadCloser.
+	body, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		return VersionInfo{}, fmt.Errorf("updater: HTTP GET %s: %w", vcu, err)
+	}
+
+	u.prevCheckTime = time.Now()
+	u.prevCheckResult, u.prevCheckError = u.parseVersionResponse(body)
+
+	return u.prevCheckResult, u.prevCheckError
+}
+
+func (u *Updater) parseVersionResponse(data []byte) (VersionInfo, error) {
+	info := VersionInfo{}
+	versionJSON := make(map[string]interface{})
+	err := json.Unmarshal(data, &versionJSON)
+	if err != nil {
+		return info, fmt.Errorf("version.json: %w", err)
+	}
+
+	var ok1, ok2, ok3, ok4 bool
+	info.NewVersion, ok1 = versionJSON["version"].(string)
+	info.Announcement, ok2 = versionJSON["announcement"].(string)
+	info.AnnouncementURL, ok3 = versionJSON["announcement_url"].(string)
+	info.SelfUpdateMinVersion, ok4 = versionJSON["selfupdate_min_version"].(string)
+	if !ok1 || !ok2 || !ok3 || !ok4 {
+		return info, fmt.Errorf("version.json: invalid data")
+	}
+
+	packageURL, ok := u.downloadURL(versionJSON)
+	if ok &&
+		info.NewVersion != u.version &&
+		strings.TrimPrefix(u.version, "v") >= strings.TrimPrefix(info.SelfUpdateMinVersion, "v") {
+		info.CanAutoUpdate = true
+	}
+
+	u.newVersion = info.NewVersion
+	u.packageURL = packageURL
+
+	return info, nil
+}
+
+// downloadURL returns the download URL for current build.
+func (u *Updater) downloadURL(json map[string]interface{}) (string, bool) {
+	var key string
+
+	if u.goarch == "arm" && u.goarm != "" {
+		key = fmt.Sprintf("download_%s_%sv%s", u.goos, u.goarch, u.goarm)
+	} else if u.goarch == "mips" && u.gomips != "" {
+		key = fmt.Sprintf("download_%s_%s_%s", u.goos, u.goarch, u.gomips)
+	}
+
+	val, ok := json[key]
+	if !ok {
+		key = fmt.Sprintf("download_%s_%s", u.goos, u.goarch)
+		val, ok = json[key]
+	}
+
+	if !ok {
+		return "", false
+	}
+
+	return val.(string), true
+}