metricSorter stops relying on time.Now and respects nil timestamps

prometheus/registry.go

@@ -32,7 +32,6 @@ import (
 	"sort"
 	"strings"
 	"sync"
-	"time"
 
 	"github.com/golang/protobuf/proto"
 	"github.com/prometheus/common/expfmt"
@@ -723,26 +722,22 @@ func (s metricSorter) Less(i, j int) bool {
 			return vi < vj
 		}
 	}
-	if s[i].GetTimestampMs() != s[j].GetTimestampMs() {
-		// While this is not strictly supported, until we have
-		// an import API some people are having some success
-		// getting data imported by supplying the same metric
-		// with different timestamps.  At the very least we
-		// shouldn't make things more difficult, so ensure that
-		// metrics get ordered by timestamp to make it possible
-		// for Prometheus to import them.
-		ti, tj := s[i].GetTimestampMs(), s[j].GetTimestampMs()
-		if ti == 0 {
-			ti = nowMillis()
-		} else if tj == 0 {
-			tj = nowMillis()
-		}
-		return ti < tj
+
+	// While this is not strictly supported, until we have an
+	// import API some people are having some success getting
+	// data imported by supplying the same metric with different
+	// timestamps.  At the very least we shouldn't make things
+	// more difficult, so ensure that metrics get ordered by
+	// timestamp so that Prometheus doesn't complain about
+	// out-of-order metrics. A missing timestamp (implies "now")
+	// will be ordered last.
+	if s[i].TimestampMs == nil && s[j].TimestampMs != nil {
+		return false
+	} else if s[i].TimestampMs != nil && s[j].TimestampMs == nil {
+		return true
+	} else if s[i].GetTimestampMs() != s[j].GetTimestampMs() {
+		return s[i].GetTimestampMs() < s[j].GetTimestampMs()
 	}
+
 	return false
 }
-
-func nowMillis() int64 {
-	now := time.Now()
-	return now.Unix()*1000 + int64(now.Nanosecond())/1000000
-}