[4189] Fix colliding filters by updating match method for MultiCharSequenceFilter to iterate through all patterns for the most complete match and not return on the first pattern found

src/metrics/filters/filter.go

@@ -585,14 +585,35 @@ func (f *multiCharSequenceFilter) matches(val []byte) ([]byte, bool) {
 		return nil, false
 	}
 
+	var matchIndex int
+	var bestPattern []byte
 	for _, pattern := range f.patterns {
-		if f.backwards && bytes.HasSuffix(val, pattern) {
-			return val[:len(val)-len(pattern)], true
+		if len(pattern) > len(val) {
+			continue
 		}
 
-		if !f.backwards && bytes.HasPrefix(val, pattern) {
-			return val[len(pattern):], true
+		if f.backwards {
+			if bytes.HasSuffix(val, pattern) {
+				if bestPattern == nil || len(pattern) > len(bestPattern) {
+					bestPattern = pattern
+					matchIndex = len(val) - len(pattern)
+				}
+			}
+		} else {
+			if bytes.HasPrefix(val, pattern) {
+				if bestPattern == nil || len(pattern) > len(bestPattern) {
+					bestPattern = pattern
+					matchIndex = len(pattern)
+				}
+			}
+		}
+	}
+
+	if bestPattern != nil {
+		if f.backwards {
+			return val[:matchIndex], true
 		}
+		return val[matchIndex:], true
 	}
 
 	return nil, false

src/metrics/filters/filter_test.go

@@ -349,6 +349,11 @@ func TestMultiCharSequenceFilter(t *testing.T) {
 	validateLookup(t, f, "12test", true, "12")
 	validateLookup(t, f, "12test2", true, "12")
 	validateLookup(t, f, "123book", true, "123")
+
+	f, err = newMultiCharSequenceFilter([]byte("arachne_failures,arachne_failures_by_rack"), false)
+	require.NoError(t, err)
+	validateLookup(t, f, "arachne_failures", true, "")
+	validateLookup(t, f, "arachne_failures_by_rack", true, "")
 }
 
 func validateLookup(t *testing.T, f chainFilter, val string, expectedMatch bool, expectedRemainder string) {