Pull request: * all: move internal Go packages to internal/

Merge in DNS/adguard-home from 2234-move-to-internal to master

Squashed commit of the following:

commit d26a288cabeac86f9483fab307677b1027c78524
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Fri Oct 30 12:44:18 2020 +0300

    * all: move internal Go packages to internal/

    Closes #2234.

internal/update/check.go

@@ -0,0 +1,104 @@
+package update
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"strings"
+	"time"
+)
+
+const versionCheckPeriod = 8 * 60 * 60
+
+// VersionInfo - VersionInfo
+type VersionInfo struct {
+	NewVersion           string // New version string
+	Announcement         string // Announcement text
+	AnnouncementURL      string // Announcement URL
+	SelfUpdateMinVersion string // Min version starting with which we can auto-update
+	CanAutoUpdate        bool   // If true - we can auto-update
+}
+
+// GetVersionResponse - downloads version.json (if needed) and deserializes it
+func (u *Updater) GetVersionResponse(forceRecheck bool) (VersionInfo, error) {
+	if !forceRecheck &&
+		u.versionCheckLastTime.Unix()+versionCheckPeriod > time.Now().Unix() {
+		return u.parseVersionResponse(u.versionJSON)
+	}
+
+	resp, err := u.Client.Get(u.VersionURL)
+	if resp != nil && resp.Body != nil {
+		defer resp.Body.Close()
+	}
+
+	if err != nil {
+		return VersionInfo{}, fmt.Errorf("updater: HTTP GET %s: %s", u.VersionURL, err)
+	}
+
+	body, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		return VersionInfo{}, fmt.Errorf("updater: HTTP GET %s: %s", u.VersionURL, err)
+	}
+
+	u.versionJSON = body
+	u.versionCheckLastTime = time.Now()
+
+	return u.parseVersionResponse(body)
+}
+
+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: %s", 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.getDownloadURL(versionJSON)
+
+	if ok &&
+		info.NewVersion != u.VersionString &&
+		strings.TrimPrefix(u.VersionString, "v") >= strings.TrimPrefix(info.SelfUpdateMinVersion, "v") {
+		info.CanAutoUpdate = true
+	}
+
+	u.NewVersion = info.NewVersion
+	u.PackageURL = packageURL
+
+	return info, nil
+}
+
+// Get download URL for the current GOOS/GOARCH/ARMVersion
+func (u *Updater) getDownloadURL(json map[string]interface{}) (string, bool) {
+	var key string
+
+	if u.Arch == "arm" && u.ARMVersion != "" {
+		// the key is:
+		// download_linux_armv5 for ARMv5
+		// download_linux_armv6 for ARMv6
+		// download_linux_armv7 for ARMv7
+		key = fmt.Sprintf("download_%s_%sv%s", u.OS, u.Arch, u.ARMVersion)
+	}
+
+	val, ok := json[key]
+	if !ok {
+		// the key is download_linux_arm or download_linux_arm64 for regular ARM versions
+		key = fmt.Sprintf("download_%s_%s", u.OS, u.Arch)
+		val, ok = json[key]
+	}
+
+	if !ok {
+		return "", false
+	}
+
+	return val.(string), true
+}