Query: Better rounding for incoming query timestamps.

CHANGELOG.md

@@ -23,6 +23,7 @@ We use *breaking* word for marking changes that are not backward compatible (rel
 - [#2936](https://github.com/thanos-io/thanos/pull/2936) Compact: Fix ReplicaLabelRemover panic when replicaLabels are not specified.
 - [#2956](https://github.com/thanos-io/thanos/pull/2956) Store: Fix fetching of chunks bigger than 16000 bytes.
 - [#2970](https://github.com/thanos-io/thanos/pull/2970) Store: Upgrade minio-go/v7 to fix slowness when running on EKS.
+- [#2976](https://github.com/thanos-io/thanos/pull/2976) Query: Better rounding for incoming query timestamps.
 
 ### Added
 

pkg/api/query/v1.go

@@ -543,6 +543,7 @@ func (qapi *QueryAPI) series(r *http.Request) (interface{}, []error, *api.ApiErr
 func parseTime(s string) (time.Time, error) {
 	if t, err := strconv.ParseFloat(s, 64); err == nil {
 		s, ns := math.Modf(t)
+		ns = math.Round(ns*1000) / 1000
 		return time.Unix(int64(s), int64(ns*float64(time.Second))), nil
 	}
 	if t, err := time.Parse(time.RFC3339Nano, s); err == nil {

pkg/api/query/v1_test.go

@@ -878,6 +878,10 @@ func TestParseTime(t *testing.T) {
 		}, {
 			input:  "2015-06-03T14:21:58.555+01:00",
 			result: ts,
+		}, {
+			// Test float rounding.
+			input:  "1543578564.705",
+			result: time.Unix(1543578564, 705*1e6),
 		},
 	}