Fix containsStringMatcher() when the text contains multiple occurrences of a substring (#431)

Signed-off-by: Marco Pracucci <marco@pracucci.com>

model/labels/regexp.go

@@ -397,27 +397,36 @@ type containsStringMatcher struct {
 func (m *containsStringMatcher) Matches(s string) bool {
 	for _, substr := range m.substrings {
 		if m.right != nil && m.left != nil {
-			pos := strings.Index(s, substr)
+			searchStartPos := 0
+
+			for {
+				pos := strings.Index(s[searchStartPos:], substr)
 				if pos < 0 {
-				continue
+					break
 				}
+
+				// Since we started searching from searchStartPos, we have to add that offset
+				// to get the actual position of the substring inside the text.
+				pos += searchStartPos
+
+				// If both the left and right matchers match, then we can stop searching because
+				// we've found a match.
 				if m.left.Matches(s[:pos]) && m.right.Matches(s[pos+len(substr):]) {
 					return true
 				}
-			continue
+
+				// Continue searching for another occurrence of the substring inside the text.
+				searchStartPos = pos + 1
 			}
+		} else if m.left != nil {
 			// If we have to check for characters on the left then we need to match a suffix.
-		if m.left != nil {
 			if strings.HasSuffix(s, substr) && m.left.Matches(s[:len(s)-len(substr)]) {
 				return true
 			}
-			continue
-		}
-		if m.right != nil {
+		} else if m.right != nil {
 			if strings.HasPrefix(s, substr) && m.right.Matches(s[len(substr):]) {
 				return true
 			}
-			continue
 		}
 	}
 	return false

model/labels/regexp_test.go

@@ -19,7 +19,6 @@ import (
 	"testing"
 	"time"
 
-	"github.com/grafana/regexp"
 	"github.com/grafana/regexp/syntax"
 	"github.com/stretchr/testify/require"
 )
@@ -60,6 +59,7 @@ var (
 		"foo", " foo bar", "bar", "buzz\nbar", "bar foo", "bfoo", "\n", "\nfoo", "foo\n", "hello foo world", "hello foo\n world", "",
 		"FOO", "Foo", "OO", "Oo", "\nfoo\n", strings.Repeat("f", 20), "prometheus", "prometheus_api_v1", "prometheus_api_v1_foo",
 		"10.0.1.20", "10.0.2.10", "10.0.3.30", "10.0.4.40",
+		"foofoo0", "foofoo",
 	}
 )
 
@@ -72,9 +72,7 @@ func TestNewFastRegexMatcher(t *testing.T) {
 				t.Parallel()
 				m, err := NewFastRegexMatcher(r)
 				require.NoError(t, err)
-				re, err := regexp.Compile("^(?:" + r + ")$")
-				require.NoError(t, err)
-				require.Equal(t, re.MatchString(v), m.MatchString(v))
+				require.Equal(t, m.re.MatchString(v), m.MatchString(v))
 			})
 		}
 
@@ -329,3 +327,24 @@ func RandStringRunes(n int) string {
 	}
 	return string(b)
 }
+
+func FuzzFastRegexMatcher_WithStaticallyDefinedRegularExpressions(f *testing.F) {
+	// Create all matchers.
+	matchers := make([]*FastRegexMatcher, 0, len(regexes))
+	for _, re := range regexes {
+		m, err := NewFastRegexMatcher(re)
+		require.NoError(f, err)
+		matchers = append(matchers, m)
+	}
+
+	// Add known values to seed corpus.
+	for _, v := range values {
+		f.Add(v)
+	}
+
+	f.Fuzz(func(t *testing.T, text string) {
+		for _, m := range matchers {
+			require.Equalf(t, m.re.MatchString(text), m.MatchString(text), "regexp: %s text: %s", m.re.String(), text)
+		}
+	})
+}