[4189] Fix colliding filters by updating match method for MultiCharSe…

…quenceFilter to iterate through all patterns for the most complete match and not return on the first pattern found (#4188)

* 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

* Remove empty newline

* Update new unit test to test length of returned byte array

* Update location of new test added to fold into an existing test

* Simplify code and add test for multiCharSequenceFilter with multiple patterns and backwards enabled

* Add benchmarks tests for new logic in multicharsequence matches method

* Add benchmark tests and optimizations to short circuit iterating through patterns if complete match is found

* Fix linting error

src/metrics/filters/filter.go

@@ -585,14 +585,43 @@ 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 len(pattern) > len(bestPattern) {
+					bestPattern = pattern
+					matchIndex = len(val) - len(pattern)
+					// No need to continue searching through remaining patterns if a complete match is found
+					if len(bestPattern) == len(val) {
+						break
+					}
+				}
+			}
+		} else {
+			if bytes.HasPrefix(val, pattern) {
+				if len(pattern) > len(bestPattern) {
+					bestPattern = pattern
+					matchIndex = len(pattern)
+					// No need to continue searching through remaining patterns if a complete match is found
+					if len(bestPattern) == len(val) {
+						break
+					}
+				}
+			}
+		}
+	}
+
+	if bestPattern != nil {
+		if f.backwards {
+			return val[:matchIndex], true
 		}
+		return val[matchIndex:], true
 	}
 
 	return nil, false

src/metrics/filters/filter_benchmark_test.go

@@ -125,6 +125,16 @@ func BenchmarkRangeFilterRangeMatchNegation(b *testing.B) {
 	benchRangeFilterRange(b, []byte("!a-z"), []byte("p"), false)
 }
 
+func BenchmarkMultiRangeFilterPrefixCollision(b *testing.B) {
+	benchMultiRangeFilter(b, []byte("test_1,test_1_suffix,extra_unused_pattern"),
+		false, [][]byte{[]byte("test_1"), []byte("test_1_suffix")})
+}
+
+func BenchmarkMultiRangeFilterSuffixCollision(b *testing.B) {
+	benchMultiRangeFilter(b, []byte("test_1,prefix_test_1,extra_unused_pattern"),
+		true, [][]byte{[]byte("test_1"), []byte("prefix_test_1")})
+}
+
 func BenchmarkMultiRangeFilterTwo(b *testing.B) {
 	benchMultiRangeFilter(b, []byte("test_1,test_2"), false, [][]byte{[]byte("test_1"), []byte("fake_1")})
 }

src/metrics/filters/filter_test.go

@@ -349,6 +349,16 @@ 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("test,test_post,extra_unused_filter"), false)
+	require.NoError(t, err)
+	validateLookup(t, f, "test", true, "")
+	validateLookup(t, f, "test_post", true, "")
+
+	f, err = newMultiCharSequenceFilter([]byte("test,pre_test,extra_unused_filter"), true)
+	require.NoError(t, err)
+	validateLookup(t, f, "test", true, "")
+	validateLookup(t, f, "pre_test", true, "")
 }
 
 func validateLookup(t *testing.T, f chainFilter, val string, expectedMatch bool, expectedRemainder string) {