Pull request: all: fix lint and naming issues

Merge in DNS/adguard-home from 2276-fix-lint to master

Updates #2276.

Squashed commit of the following:

commit 433f44cc7b674a20ed60a9d29466ba888b3ef66e
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Mon Dec 7 14:14:28 2020 +0300

    querylog: improve code and documentation

commit 851df97d2a87de5e7180a502055ee6f1a6defdca
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Fri Dec 4 20:36:32 2020 +0300

    all: fix lint and naming issues

internal/stats/http.go

@@ -0,0 +1,103 @@
+// HTTP request handlers for accessing statistics data and configuration settings
+
+package stats
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"time"
+
+	"github.com/AdguardTeam/golibs/log"
+)
+
+func httpError(r *http.Request, w http.ResponseWriter, code int, format string, args ...interface{}) {
+	text := fmt.Sprintf(format, args...)
+
+	log.Info("Stats: %s %s: %s", r.Method, r.URL, text)
+
+	http.Error(w, text, code)
+}
+
+// Return data
+func (s *statsCtx) handleStats(w http.ResponseWriter, r *http.Request) {
+	start := time.Now()
+	d := s.getData()
+	log.Debug("Stats: prepared data in %v", time.Since(start))
+
+	if d == nil {
+		httpError(r, w, http.StatusInternalServerError, "Couldn't get statistics data")
+		return
+	}
+
+	data, err := json.Marshal(d)
+	if err != nil {
+		httpError(r, w, http.StatusInternalServerError, "json encode: %s", err)
+		return
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+
+	_, err = w.Write(data)
+	if err != nil {
+		httpError(r, w, http.StatusInternalServerError, "json encode: %s", err)
+
+		return
+	}
+}
+
+type config struct {
+	IntervalDays uint32 `json:"interval"`
+}
+
+// Get configuration
+func (s *statsCtx) handleStatsInfo(w http.ResponseWriter, r *http.Request) {
+	resp := config{}
+	resp.IntervalDays = s.conf.limit / 24
+
+	data, err := json.Marshal(resp)
+	if err != nil {
+		httpError(r, w, http.StatusInternalServerError, "json encode: %s", err)
+		return
+	}
+	w.Header().Set("Content-Type", "application/json")
+	_, err = w.Write(data)
+	if err != nil {
+		httpError(r, w, http.StatusInternalServerError, "http write: %s", err)
+	}
+}
+
+// Set configuration
+func (s *statsCtx) handleStatsConfig(w http.ResponseWriter, r *http.Request) {
+	reqData := config{}
+	err := json.NewDecoder(r.Body).Decode(&reqData)
+	if err != nil {
+		httpError(r, w, http.StatusBadRequest, "json decode: %s", err)
+		return
+	}
+
+	if !checkInterval(reqData.IntervalDays) {
+		httpError(r, w, http.StatusBadRequest, "Unsupported interval")
+		return
+	}
+
+	s.setLimit(int(reqData.IntervalDays))
+	s.conf.ConfigModified()
+}
+
+// Reset data
+func (s *statsCtx) handleStatsReset(w http.ResponseWriter, r *http.Request) {
+	s.clear()
+}
+
+// Register web handlers
+func (s *statsCtx) initWeb() {
+	if s.conf.HTTPRegister == nil {
+		return
+	}
+
+	s.conf.HTTPRegister("GET", "/control/stats", s.handleStats)
+	s.conf.HTTPRegister("POST", "/control/stats_reset", s.handleStatsReset)
+	s.conf.HTTPRegister("POST", "/control/stats_config", s.handleStatsConfig)
+	s.conf.HTTPRegister("GET", "/control/stats_info", s.handleStatsInfo)
+}