lib/promutils.ParseTime(): add support for timestamps in milliseconds

See https://stackoverflow.com/questions/76437098/how-to-handle-time-unit-and-step-while-ingesting-or-querying-in-victoriametrics/76438405

Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/4459

README.md

@@ -823,6 +823,7 @@ in [query APIs](https://docs.victoriametrics.com/#prometheus-querying-api-usage)
 in [export APIs](https://docs.victoriametrics.com/#how-to-export-time-series).
 
 - Unix timestamps in seconds with optional milliseconds after the point. For example, `1562529662.678`.
+- Unix timestamps in milliseconds. For example, `1562529662678`.
 - [RFC3339](https://www.ietf.org/rfc/rfc3339.txt). For example, `2022-03-29T01:02:03Z` or `2022-03-29T01:02:03+02:30`.
 - Partial RFC3339. Examples: `2022`, `2022-03`, `2022-03-29`, `2022-03-29T01`, `2022-03-29T01:02`, `2022-03-29T01:02:03`.
   The partial RFC3339 time is in UTC timezone by default. It is possible to specify timezone there by adding `+hh:mm` or `-hh:mm` suffix to partial time.

docs/CHANGELOG.md

@@ -32,6 +32,7 @@ The following tip changes can be tested by building VictoriaMetrics components f
 * FEATURE: [vmctl](https://docs.victoriametrics.com/vmctl.html): update backoff policy on retries to reduce probability of overloading for `source` or `destination` databases. See [this pull request](https://github.com/VictoriaMetrics/VictoriaMetrics/pull/4442).
 * FEATURE: vmstorage: suppress "broken pipe" errors for search queries on vmstorage side. See [this commit](https://github.com/VictoriaMetrics/VictoriaMetrics/pull/4418/commits/a6a7795b9e1f210d614a2c5f9a3016b97ded4792).
 * FEATURE: [Official Grafana dashboards for VictoriaMetrics](https://grafana.com/orgs/victoriametrics): add panel for tracking rate of syscalls while writing or reading from disk via `process_io_(read|write)_syscalls_total` metrics.
+* FEATURE: accept timestamps in milliseconds at `start`, `end` and `time` query args in [Prometheus querying API](https://docs.victoriametrics.com/#prometheus-querying-api-usage). See [these docs](https://docs.victoriametrics.com/#timestamp-formats) and [this feature request](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/4459).
 
 * BUGFIX: add the following command-line flags, which can be used for limiting Graphite API calls: 
   `--search.maxGraphiteTagKeys` for limiting the number of tag keys returned from Graphite `/tags`, `/tags/autoComplete/*`, `/tags/findSeries` API. 

docs/README.md

@@ -826,6 +826,7 @@ in [query APIs](https://docs.victoriametrics.com/#prometheus-querying-api-usage)
 in [export APIs](https://docs.victoriametrics.com/#how-to-export-time-series).
 
 - Unix timestamps in seconds with optional milliseconds after the point. For example, `1562529662.678`.
+- Unix timestamps in milliseconds. For example, `1562529662678`.
 - [RFC3339](https://www.ietf.org/rfc/rfc3339.txt). For example, `2022-03-29T01:02:03Z` or `2022-03-29T01:02:03+02:30`.
 - Partial RFC3339. Examples: `2022`, `2022-03`, `2022-03-29`, `2022-03-29T01`, `2022-03-29T01:02`, `2022-03-29T01:02:03`.
   The partial RFC3339 time is in UTC timezone by default. It is possible to specify timezone there by adding `+hh:mm` or `-hh:mm` suffix to partial time.

docs/Single-server-VictoriaMetrics.md

@@ -834,6 +834,7 @@ in [query APIs](https://docs.victoriametrics.com/#prometheus-querying-api-usage)
 in [export APIs](https://docs.victoriametrics.com/#how-to-export-time-series).
 
 - Unix timestamps in seconds with optional milliseconds after the point. For example, `1562529662.678`.
+- Unix timestamps in milliseconds. For example, `1562529662678`.
 - [RFC3339](https://www.ietf.org/rfc/rfc3339.txt). For example, `2022-03-29T01:02:03Z` or `2022-03-29T01:02:03+02:30`.
 - Partial RFC3339. Examples: `2022`, `2022-03`, `2022-03-29`, `2022-03-29T01`, `2022-03-29T01:02`, `2022-03-29T01:02:03`.
   The partial RFC3339 time is in UTC timezone by default. It is possible to specify timezone there by adding `+hh:mm` or `-hh:mm` suffix to partial time.

lib/promutils/time.go

@@ -70,8 +70,16 @@ func ParseTimeAt(s string, currentTimestamp float64) (float64, error) {
 		return tzOffset + float64(t.UnixNano())/1e9, nil
 	}
 	if !strings.Contains(sOrig, "-") {
-		// Parse the timestamp in seconds
-		return strconv.ParseFloat(sOrig, 64)
+		// Parse the timestamp in seconds or in milliseconds
+		ts, err := strconv.ParseFloat(sOrig, 64)
+		if err != nil {
+			return 0, err
+		}
+		if ts >= (1 << 32) {
+			// The timestamp is in milliseconds. Convert it to seconds.
+			ts /= 1000
+		}
+		return ts, nil
 	}
 	if len(s) == 7 {
 		// Parse YYYY-MM

lib/promutils/time_test.go

@@ -19,6 +19,13 @@ func TestParseTimeAtSuccess(t *testing.T) {
 
 	now := float64(time.Now().UnixNano()) / 1e9
 
+	// unix timestamp in seconds
+	f("1562529662", now, 1562529662)
+	f("1562529662.678", now, 1562529662.678)
+
+	// unix timestamp in milliseconds
+	f("1562529662678", now, 1562529662.678)
+
 	// duration relative to the current time
 	f("now", now, now)
 	f("1h5s", now, now-3605)