cherry-pick: 4142 stats panic

Merge in DNS/adguard-home from 4142-stats-panic to master

Updates #4142.

Squashed commit of the following:

commit bf168f50ac86bdfdab73bf7285705f09f87b6c72
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Jan 20 17:13:41 2022 +0300

    stats: imp more

commit bb638211da7d0c51959ded2dacb72faea00befb4
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Jan 20 17:09:31 2022 +0300

    stats: imp code quality

commit 27ac52f15e4e0f4112ce7a6b47b03f963463393e
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Jan 20 17:00:09 2022 +0300

    stats: recover panic on init

commit 1ffcebbb9062438170b010e1c7bad3c6cef4cfc1
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Jan 20 14:19:01 2022 +0300

    all: fix some typos

CHANGELOG.md

@@ -51,7 +51,7 @@ and this project adheres to
 
 
 <!--
-## [v0.107.3] - 2022-01-19 (APPROX.)
+## [v0.107.3] - 2022-02-08 (APPROX.)
 -->
 
 

internal/aghalg/aghalg.go

@@ -24,7 +24,7 @@ func (uc UniqChecker) Add(elems ...comparable) {
 	}
 }
 
-// Merge returns a validator containing data from both v and other.
+// Merge returns a checker containing data from both uc and other.
 func (uc UniqChecker) Merge(other UniqChecker) (merged UniqChecker) {
 	merged = make(UniqChecker, len(uc)+len(other))
 	for elem, num := range uc {

internal/home/controlinstall.go

@@ -128,7 +128,7 @@ func (req *checkConfReq) validateWeb(uc aghalg.UniqChecker) (err error) {
 }
 
 // validateDNS returns error if the DNS part of the initial configuration can't
-// be set.  autofix is true if the port can be unbound by AdGuard Home
+// be set.  canAutofix is true if the port can be unbound by AdGuard Home
 // automatically.
 func (req *checkConfReq) validateDNS(uc aghalg.UniqChecker) (canAutofix bool, err error) {
 	defer func() { err = errors.Annotate(err, "validating ports: %w") }()

internal/home/dns.go

@@ -54,7 +54,7 @@ func initDNSServer() (err error) {
 	}
 	Context.stats, err = stats.New(statsConf)
 	if err != nil {
-		return fmt.Errorf("couldn't initialize statistics module")
+		return fmt.Errorf("init stats: %w", err)
 	}
 
 	conf := querylog.Config{

internal/stats/unit.go

@@ -67,7 +67,29 @@ type unitDB struct {
 	TimeAvg uint32 // usec
 }
 
+// withRecovered turns the value recovered from panic if any into an error and
+// combines it with the one pointed by orig.  orig must be non-nil.
+func withRecovered(orig *error) {
+	p := recover()
+	if p == nil {
+		return
+	}
+
+	var err error
+	switch p := p.(type) {
+	case error:
+		err = fmt.Errorf("panic: %w", p)
+	default:
+		err = fmt.Errorf("panic: recovered value of type %[1]T: %[1]v", p)
+	}
+
+	*orig = errors.WithDeferred(*orig, err)
+}
+
+// createObject creates s from conf and properly initializes it.
 func createObject(conf Config) (s *statsCtx, err error) {
+	defer withRecovered(&err)
+
 	s = &statsCtx{
 		mu: &sync.Mutex{},
 	}