From e5868b9c29f65c0a097ecdbe72bec2470d6810b2 Mon Sep 17 00:00:00 2001
From: jduncan0000 <jduncan0000@gmail.com>
Date: Fri, 18 Mar 2022 05:58:22 -0500
Subject: [PATCH] Fix for issue #2255 - matchTagFilters for positive
 empty-match filters (#2304)

* fix for issue 2255 - matchTagFilters for positive empty-match filters

* add example to comments

* formatting

* add test for positive empty match

* formatting
---
 lib/storage/index_db.go      | 10 ++++++++--
 lib/storage/index_db_test.go | 13 +++++++++++++
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/lib/storage/index_db.go b/lib/storage/index_db.go
index 77e1c27821..b470db59ac 100644
--- a/lib/storage/index_db.go
+++ b/lib/storage/index_db.go
@@ -2152,14 +2152,20 @@ func matchTagFilters(mn *MetricName, tfs []*tagFilter, kb *bytesutil.ByteBuffer)
 			tagMatched = true
 			break
 		}
-		if !tagSeen && tf.isNegative && !tf.isEmptyMatch {
+		if !tagSeen && (!tf.isNegative && tf.isEmptyMatch || tf.isNegative && !tf.isEmptyMatch) {
+			// tf contains positive empty-match filter for non-existing tag key, i.e.
+			// {non_existing_tag_key=~"foobar|"}
+			//
+			// OR
+			//
 			// tf contains negative filter for non-exsisting tag key
 			// and this filter doesn't match empty string, i.e. {non_existing_tag_key!="foobar"}
 			// Such filter matches anything.
 			//
 			// Note that the filter `{non_existing_tag_key!~"|foobar"}` shouldn't match anything,
 			// since it is expected that it matches non-empty `non_existing_tag_key`.
-			// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/546 for details.
+			// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/546 and
+			// https://github.com/VictoriaMetrics/VictoriaMetrics/issues/2255 for details.
 			continue
 		}
 		if tagMatched {
diff --git a/lib/storage/index_db_test.go b/lib/storage/index_db_test.go
index 1f79360f04..72ecec2fab 100644
--- a/lib/storage/index_db_test.go
+++ b/lib/storage/index_db_test.go
@@ -1182,6 +1182,19 @@ func TestMatchTagFilters(t *testing.T) {
 		t.Fatalf("Should match")
 	}
 
+	// Positive empty match by non-existing tag
+	tfs.Reset()
+	if err := tfs.Add([]byte("non-existing-tag"), []byte("foobar|"), false, true); err != nil {
+		t.Fatalf("cannot add regexp, positive filter: %s", err)
+	}
+	ok, err = matchTagFilters(&mn, toTFPointers(tfs.tfs), &bb)
+	if err != nil {
+		t.Fatalf("unexpected error: %s", err)
+	}
+	if !ok {
+		t.Fatalf("Should match")
+	}
+
 	// Negative match by non-existing tag
 	tfs.Reset()
 	if err := tfs.Add([]byte("non-existing-tag"), []byte("foobar"), false, false); err != nil {