Added validation for timestamp according to nmea spec

Author: klyve

tagblock.go

@@ -1,10 +1,12 @@
 package nmea
 
 import (
+	"errors"
 	"fmt"
 	"regexp"
 	"strconv"
 	"strings"
+	"time"
 )
 
 const (
@@ -42,13 +44,30 @@ type TagBlock struct {
 }
 
 func parseInt64(raw string) (int64, error) {
-	i, err := strconv.ParseInt(raw[2:], 10, 32)
+	i, err := strconv.ParseInt(raw[2:], 10, 64)
 	if err != nil {
 		return 0, fmt.Errorf("nmea: tagblock unable to parse uint32 [%s]", raw)
 	}
 	return i, nil
 }
 
+// Timestamp can come as milliseconds or seconds
+func validUnixTimestamp(timestamp int64) (int64, error) {
+	if timestamp < 0 {
+		return 0, errors.New("nmea: Tagblock timestamp is not valid must be between 0 and now + 24h")
+	}
+	now := time.Now()
+	unix := now.Unix() + 24*3600
+	if timestamp > unix {
+		if timestamp > unix*1000 {
+			return 0, errors.New("nmea: Tagblock timestamp is not valid")
+		}
+		return timestamp / 1000, nil
+	}
+
+	return timestamp, nil
+}
+
 // parseTagBlock adds support for tagblocks
 // https://rietman.wordpress.com/2016/09/17/nemastudio-now-supports-the-nmea-0183-tag-block/
 func parseTagBlock(raw string) (TagBlock, string, error) {
@@ -90,6 +109,10 @@ func parseTagBlock(raw string) (TagBlock, string, error) {
 			if err != nil {
 				return tagBlock, raw, err
 			}
+			tagBlock.Time, err = validUnixTimestamp(tagBlock.Time)
+			if err != nil {
+				return tagBlock, raw, err
+			}
 		case TypeDestinationID:
 			tagBlock.Destination = item[2:]
 		case TypeGrouping:

tagblock_test.go

@@ -41,6 +41,37 @@ var tagblocktests = []struct {
 			Head:   "UdPbC?",
 		},
 	},
+	{
+		name: "Test unix timestamp",
+		raw:  "UdPbC?\\x:NorSat_1,c:1564827317*42\\!AIVDM,1,1,,A,19NSRaP02A0fo91kwnaMKbjR08:J,0*15",
+		msg: TagBlock{
+			Time:   1564827317,
+			Source: "",
+			Head:   "UdPbC?",
+		},
+	},
+	{
+
+		name: "Test milliseconds timestamp",
+		raw:  "UdPbC?\\x:NorSat_1,c:1564827317000*72\\!AIVDM,1,1,,A,19NSRaP02A0fo91kwnaMKbjR08:J,0*15",
+		msg: TagBlock{
+			Time:   1564827317,
+			Source: "",
+			Head:   "UdPbC?",
+		},
+	},
+	{
+
+		name: "Test invalid high timestamp",
+		raw:  "UdPbC?\\x:NorSat_1,c:25648273170000000*71\\!AIVDM,1,1,,A,19NSRaP02A0fo91kwnaMKbjR08:J,0*15",
+		err:  "nmea: Tagblock timestamp is not valid",
+	},
+	{
+
+		name: "Test invalid low timestamp",
+		raw:  "UdPbC?\\x:NorSat_1,c:-10*60\\!AIVDM,1,1,,A,19NSRaP02A0fo91kwnaMKbjR08:J,0*15",
+		err:  "nmea: Tagblock timestamp is not valid must be between 0 and now + 24h",
+	},
 	{
 
 		name: "Test all input types",