Add support of ntp time verification

Gopkg.lock

@@ -16,6 +16,12 @@
   packages = ["."]
   revision = "2efee857e7cfd4f3d0138cc3cbb1b4966962b93a"
 
+[[projects]]
+  name = "github.com/beevik/ntp"
+  packages = ["."]
+  revision = "62c80a04de2086884d8296004b6d74ee1846c582"
+  version = "v0.2.0"
+
 [[projects]]
   name = "github.com/davecgh/go-spew"
   packages = ["spew"]
@@ -77,6 +83,17 @@
   revision = "eeedf312bc6c57391d84767a4cd413f02a917974"
   version = "v1.8.0"
 
+[[projects]]
+  branch = "master"
+  name = "golang.org/x/net"
+  packages = [
+    "bpf",
+    "internal/iana",
+    "internal/socket",
+    "ipv4"
+  ]
+  revision = "d0887baf81f4598189d4e12a37c6da86f0bba4d0"
+
 [[projects]]
   name = "gopkg.in/alecthomas/kingpin.v2"
   packages = ["."]
@@ -86,6 +103,6 @@
 [solve-meta]
   analyzer-name = "dep"
   analyzer-version = 1
-  inputs-digest = "c4fdd3664f683342ad0c2509f4a8bcfe5b267a6e8cdaf36f70d39536bbf89834"
+  inputs-digest = "f828340a30ea13c563829f9a37d0ff62974d4578411c9be02e61125dbdf98692"
   solver-name = "gps-cdcl"
   solver-version = 1

Gopkg.toml

@@ -48,3 +48,7 @@
 [[constraint]]
   branch = "master"
   name = "github.com/dustin/go-humanize"
+
+[[constraint]]
+  name = "github.com/beevik/ntp"
+  version = "0.2.0"

main.go

@@ -4,20 +4,22 @@ package main
 
 import (
 	"encoding/json"
+	"fmt"
 	"io"
 	"math/rand"
 	"os"
 	"syscall"
 	"time"
 
+	"github.com/juju/errors"
 	"go.uber.org/zap"
 	"go.uber.org/zap/zapcore"
 	kingpin "gopkg.in/alecthomas/kingpin.v2"
 
 	"github.com/9seconds/mtg/config"
+	"github.com/9seconds/mtg/ntp"
 	"github.com/9seconds/mtg/proxy"
 	"github.com/9seconds/mtg/stats"
-	"github.com/juju/errors"
 )
 
 var (
@@ -120,6 +122,14 @@ func main() {
 
 	if conf.UseMiddleProxy() {
 		zap.S().Infow("Use middle proxy connection to Telegram")
+		if diff, err := ntp.Fetch(); err != nil {
+			zap.S().Warnw("Could not fetch time data from NTP")
+		} else {
+			if diff >= time.Second {
+				usage(fmt.Sprintf("You choose to use middle proxy but your clock drift (%s) is bigger than 1 second. Please, sync your time", diff))
+			}
+			go ntp.AutoUpdate()
+		}
 	} else {
 		zap.S().Infow("Use direct connection to Telegram")
 	}

ntp/ntp.go

@@ -0,0 +1,60 @@
+package ntp
+
+import (
+	"math/rand"
+	"time"
+
+	"github.com/beevik/ntp"
+	"github.com/juju/errors"
+	"go.uber.org/zap"
+)
+
+const autoUpdatePeriod = time.Minute
+
+var ntpEndpoints = []string{
+	"0.pool.ntp.org",
+	"1.pool.ntp.org",
+	"2.pool.ntp.org",
+	"3.pool.ntp.org",
+}
+
+// Fetch fetches the data on time drift.
+func Fetch() (time.Duration, error) {
+	url := ntpEndpoints[rand.Intn(len(ntpEndpoints))]
+	resp, err := ntp.Query(url)
+	if err != nil {
+		return 0, errors.Annotatef(err, "Cannot fetch NTP server %s", url)
+	}
+
+	offsetInt := int64(resp.ClockOffset)
+	if offsetInt < 0 {
+		offsetInt = -offsetInt
+	}
+	offset := time.Duration(offsetInt)
+
+	return offset, nil
+}
+
+// AutoUpdate runs periodic check of current time .drift state.
+func AutoUpdate() {
+	logger := zap.S().Named("ntp")
+
+	for range time.Tick(autoUpdatePeriod) {
+		diff, err := Fetch()
+		if err != nil {
+			logger.Debugw("Cannot fetch time from NTP", "error", err)
+			continue
+		}
+
+		switch {
+		case diff < 400*time.Millisecond:
+			logger.Debugw("NTP time drift", "value", diff.String())
+		case diff < 600*time.Millisecond:
+			logger.Infow("NTP time drift", "value", diff.String())
+		case diff < 800*time.Millisecond:
+			logger.Warnw("NTP time drift", "value", diff.String())
+		default:
+			logger.Errorw("NTP time drift", "value", diff.String())
+		}
+	}
+}