lib/logstorage: allow specifying _time filter offset without time range

This is useful when builiding graphs on time ranges in the past.

docs/VictoriaLogs/CHANGELOG.md

@@ -16,6 +16,7 @@ according to [these docs](https://docs.victoriametrics.com/victorialogs/quicksta
 ## tip
 
 * FEATURE: [`join` pipe](https://docs.victoriametrics.com/victorialogs/logsql/#join-pipe): add an ability to add prefix to all the log field names from the joined query, by using `| join by (<by_fields>) (<query>) prefix "some_prefix"` syntax.
+* FEATURE: [`_time` filter](https://docs.victoriametrics.com/victorialogs/logsql/#time-filter): allow specifying offset without time range. For example, `_time:offset 1d` matches all the logs until `now-1d` in the [`_time` field](https://docs.victoriametrics.com/victorialogs/keyconcepts/#time-field). This is useful when building graphs for time ranges with some offset in the past.
 
 ## [v0.41.0](https://github.com/VictoriaMetrics/VictoriaMetrics/releases/tag/v0.41.0-victorialogs)
 

docs/VictoriaLogs/LogsQL.md

@@ -316,6 +316,7 @@ For example, `_time:2023-10-20` matches all the logs for `2023-10-20` day accord
 
 It is possible to specify generic offset for the selected time range by appending `offset` after the `_time` filter. Examples:
 
+- `_time:offset 1h` matches logs until `now-1h`.
 - `_time:5m offset 1h` matches logs on the time range `(now-1h5m, now-1h]`.
 - `_time:2023-07Z offset 5h30m` matches logs on July, 2023 by UTC with offset 5h30m.
 - `_time:[2023-02-01Z, 2023-03-01Z) offset 1w` matches logs the week before the time range `[2023-02-01Z, 2023-03-01Z)` by UTC.

lib/logstorage/parser.go

@@ -2074,6 +2074,20 @@ func getWeekRangeArg(lex *lexer) (time.Weekday, string, error) {
 }
 
 func parseFilterTimeRange(lex *lexer) (*filterTime, error) {
+	if lex.isKeyword("offset") {
+		ft := &filterTime{
+			minTimestamp: math.MinInt64,
+			maxTimestamp: lex.currentTimestamp,
+		}
+		offset, offsetStr, err := parseTimeOffset(lex)
+		if err != nil {
+			return nil, fmt.Errorf("cannot parse offset for _time filter []: %w", err)
+		}
+		ft.maxTimestamp -= offset
+		ft.stringRepr = offsetStr
+		return ft, nil
+	}
+
 	ft, err := parseFilterTime(lex)
 	if err != nil {
 		return nil, err
@@ -2081,20 +2095,33 @@ func parseFilterTimeRange(lex *lexer) (*filterTime, error) {
 	if !lex.isKeyword("offset") {
 		return ft, nil
 	}
+
+	offset, offsetStr, err := parseTimeOffset(lex)
+	if err != nil {
+		return nil, fmt.Errorf("cannot parse offset for _time filter [%s]: %w", ft, err)
+	}
+	ft.minTimestamp -= offset
+	ft.maxTimestamp -= offset
+	ft.stringRepr += " " + offsetStr
+	return ft, nil
+}
+
+func parseTimeOffset(lex *lexer) (int64, string, error) {
+	if !lex.isKeyword("offset") {
+		return 0, "", fmt.Errorf("unexpected token %q; want 'offset'", lex.token)
+	}
 	lex.nextToken()
+
 	s, err := getCompoundToken(lex)
 	if err != nil {
-		return nil, fmt.Errorf("cannot parse offset in _time filter: %w", err)
+		return 0, "", err
 	}
 	d, ok := tryParseDuration(s)
 	if !ok {
-		return nil, fmt.Errorf("cannot parse offset %q for _time filter %s", s, ft)
+		return 0, "", fmt.Errorf("cannot parse duration [%s]", s)
 	}
 	offset := int64(d)
-	ft.minTimestamp -= offset
-	ft.maxTimestamp -= offset
-	ft.stringRepr += " offset " + s
-	return ft, nil
+	return offset, "offset " + s, nil
 }
 
 func parseFilterTime(lex *lexer) (*filterTime, error) {

lib/logstorage/parser_test.go

@@ -761,7 +761,9 @@ func TestParseQuerySuccess(t *testing.T) {
 	f(`_time:[2023-01-05, 2023-01-06) OFFset 5m`, `_time:[2023-01-05,2023-01-06) offset 5m`)
 	f(`_time:(2023-01-05, 2023-01-06] OFFset 5m`, `_time:(2023-01-05,2023-01-06] offset 5m`)
 	f(`_time:(2023-01-05, 2023-01-06) OFFset 5m`, `_time:(2023-01-05,2023-01-06) offset 5m`)
-	f(`_time:1h offset 5m`, `_time:1h offset 5m`)
+	f(`_time:1h offset 5.3m`, `_time:1h offset 5.3m`)
+	f(`_time:offset 1d`, `_time:offset 1d`)
+	f(`_time:offset -1.5d`, `_time:offset -1.5d`)
 	f(`_time:1h "offSet"`, `_time:1h "offSet"`) // "offset" is a search word, since it is quoted
 	f(`_time:1h (Offset)`, `_time:1h "Offset"`) // "offset" is a search word, since it is in parens
 	f(`_time:1h "and"`, `_time:1h "and"`)       // "and" is a search word, since it is quoted
@@ -1356,6 +1358,8 @@ func TestParseQueryFailure(t *testing.T) {
 	f("_time:234foo")
 	f("_time:5m offset")
 	f("_time:10m offset foobar")
+	f("_time:offset")
+	f("_time:offset foobar")
 
 	// invalid day_range filters
 	f("_time:day_range")
@@ -1373,7 +1377,7 @@ func TestParseQueryFailure(t *testing.T) {
 	f("_time:week_range[Mon,")
 	f("_time:week_range[Mon,bar")
 	f("_time:week_range[Mon,Fri")
-	f("_time:week_range[Mon,Fri] offset")
+	f("_time:week_range[Mon,Fri] offset foobar")
 
 	// long query with error
 	f(`very long query with error aaa ffdfd fdfdfd fdfd:( ffdfdfdfdfd`)