Convert time readers to represent time in UTC.

Go's time.Time represents time as UTC in its fundamental data type.
That said, when using ``time.Unix(...)``, it sets the zone for the
time representation to the local.  Unfortunately with diagnosis and
our tests, it is a PITA to jump between various zones, even though
the serialized version remains the same.

To keep things easy, all places where times are generated or read
are converted into UTC.  These conversions are cheap, for
``Time.In`` merely changes a pointer reference in the struct,
nothing more.  This enables me to diagnose test failures with fixture
data very easily.

coding/indexable/time.go

@@ -18,14 +18,14 @@ import (
 	"time"
 )
 
-var (
-	EarliestTime = EncodeTime(time.Time{})
-)
-
+// EncodeTimeInto writes the provided time into the specified buffer subject
+// to the LevelDB big endian key sort order requirement.
 func EncodeTimeInto(dst []byte, t time.Time) {
 	binary.BigEndian.PutUint64(dst, uint64(t.Unix()))
 }
 
+// EncodeTime converts the provided time into a byte buffer subject to the
+// LevelDB big endian key sort order requirement.
 func EncodeTime(t time.Time) []byte {
 	buffer := make([]byte, 8)
 
@@ -34,6 +34,8 @@ func EncodeTime(t time.Time) []byte {
 	return buffer
 }
 
+// DecodeTime deserializes a big endian byte array into a Unix time in UTC,
+// omitting granularity precision less than a second.
 func DecodeTime(src []byte) time.Time {
-	return time.Unix(int64(binary.BigEndian.Uint64(src)), 0)
+	return time.Unix(int64(binary.BigEndian.Uint64(src)), 0).UTC()
 }

model/metric.go

@@ -139,7 +139,7 @@ func (v Values) InsideInterval(t time.Time) (s bool) {
 func NewValuesFromDTO(dto *dto.SampleValueSeries) (v Values) {
 	for _, value := range dto.Value {
 		v = append(v, SamplePair{
-			Timestamp: time.Unix(*value.Timestamp, 0),
+			Timestamp: time.Unix(*value.Timestamp, 0).UTC(),
 			Value:     SampleValue(*value.Value),
 		})
 	}

model/samplekey.go

@@ -73,7 +73,7 @@ func NewSampleKeyFromDTO(dto *dto.SampleKey) SampleKey {
 	return SampleKey{
 		Fingerprint:    NewFingerprintFromDTO(dto.Fingerprint),
 		FirstTimestamp: indexable.DecodeTime(dto.Timestamp),
-		LastTimestamp:  time.Unix(*dto.LastTimestamp, 0),
+		LastTimestamp:  time.Unix(*dto.LastTimestamp, 0).UTC(),
 		SampleCount:    *dto.SampleCount,
 	}
 }

model/watermark.go

@@ -37,7 +37,7 @@ func (w Watermark) ToMetricHighWatermarkDTO() *dto.MetricHighWatermark {
 // dto.MetricHighWatermark object.
 func NewWatermarkFromHighWatermarkDTO(d *dto.MetricHighWatermark) Watermark {
 	return Watermark{
-		time.Unix(*d.Timestamp, 0),
+		time.Unix(*d.Timestamp, 0).UTC(),
 	}
 }
 

web/api/query.go

@@ -84,8 +84,8 @@ func (serv MetricsService) QueryRange(expr string, end int64, duration int64, st
 
 	matrix, err := ast.EvalVectorRange(
 		exprNode.(ast.VectorNode),
-		time.Unix(end-duration, 0),
-		time.Unix(end, 0),
+		time.Unix(end-duration, 0).UTC(),
+		time.Unix(end, 0).UTC(),
 		time.Duration(step)*time.Second)
 	if err != nil {
 		return ast.ErrorToJSON(err)