From 58c1c2dfc2c197409bbecae7c7f5b71ea07fbda2 Mon Sep 17 00:00:00 2001
From: Augustin Husson <husson.augustin@gmail.com>
Date: Thu, 5 Dec 2024 15:45:51 +0100
Subject: [PATCH] Improve matching regexp to avoid situation where it matches
 everything (#34)

Signed-off-by: Augustin Husson <husson.augustin@gmail.com>
---
 database/database.go      | 18 ++++++++++++++++--
 database/database_test.go |  9 +++++++++
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/database/database.go b/database/database.go
index e803c2b..ad3ce8e 100644
--- a/database/database.go
+++ b/database/database.go
@@ -290,7 +290,7 @@ func (d *db) matchValidMetric(validMetric string) {
 				continue
 			}
 		}
-		if re.MatchString(validMetric) {
+		if isMatching(re, validMetric) {
 			matchingMetrics := partialMetric.MatchingMetrics
 			if matchingMetrics == nil {
 				matchingMetrics = v1.NewSet[string]()
@@ -301,7 +301,7 @@ func (d *db) matchValidMetric(validMetric string) {
 	}
 }
 
-// GenerateRegexp is taking an partial metric name,
+// GenerateRegexp is taking a partial metric name,
 // will replace every variable by a pattern and then returning a regepx if the final string is not just equal to .*.
 func generateRegexp(partialMetricName string) (*common.Regexp, error) {
 	// The first step is to replace every variable by a single special char.
@@ -331,3 +331,17 @@ func generateRegexp(partialMetricName string) (*common.Regexp, error) {
 	re, err := common.NewRegexp(fmt.Sprintf("^%s$", compileString))
 	return &re, err
 }
+
+func isMatching(re *common.Regexp, metric string) bool {
+	if !re.MatchString(metric) {
+		return false
+	}
+	// We are taking some time to look at what is matching.
+	// We are doing that to avoid the situation where this regexp `foo|` is matching everything.
+	for _, match := range re.FindAllString(metric, -1) {
+		if len(match) > 0 {
+			return true
+		}
+	}
+	return false
+}
diff --git a/database/database_test.go b/database/database_test.go
index 188025f..526dd77 100644
--- a/database/database_test.go
+++ b/database/database_test.go
@@ -66,3 +66,12 @@ func TestGenerateRegexp(t *testing.T) {
 		})
 	}
 }
+
+func TestIsMatching(t *testing.T) {
+	re, _ := generateRegexp("foo|")
+	assert.False(t, isMatching(re, "bar"))
+	assert.True(t, isMatching(re, "foo"))
+
+	re, _ = generateRegexp("foo|bar")
+	assert.True(t, isMatching(re, "bar"))
+}