Fix: handle nil variableLabels in Desc.String() method and add tests …

…for nil label values Fixes #1684 Signed-off-by: Kemal Akkoyun <[email protected]>
prometheus · Nov 19, 2024 · 1e590c2 · 1e590c2
1 parent 291b0b0
commit 1e590c2
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Showing 2 changed files with 43 additions and 6 deletions.
diff --git a/prometheus/desc.go b/prometheus/desc.go
@@ -189,12 +189,15 @@ func (d *Desc) String() string {
 			fmt.Sprintf("%s=%q", lp.GetName(), lp.GetValue()),
 		)
 	}
-	vlStrings := make([]string, 0, len(d.variableLabels.names))
-	for _, vl := range d.variableLabels.names {
-		if fn, ok := d.variableLabels.labelConstraints[vl]; ok && fn != nil {
-			vlStrings = append(vlStrings, fmt.Sprintf("c(%s)", vl))
-		} else {
-			vlStrings = append(vlStrings, vl)
+	vlStrings := []string{}
+	if d.variableLabels != nil {
+		vlStrings = make([]string, 0, len(d.variableLabels.names))
+		for _, vl := range d.variableLabels.names {
+			if fn, ok := d.variableLabels.labelConstraints[vl]; ok && fn != nil {
+				vlStrings = append(vlStrings, fmt.Sprintf("c(%s)", vl))
+			} else {
+				vlStrings = append(vlStrings, vl)
+			}
 		}
 	}
 	return fmt.Sprintf(

diff --git a/prometheus/desc_test.go b/prometheus/desc_test.go
@@ -28,3 +28,37 @@ func TestNewDescInvalidLabelValues(t *testing.T) {
 		t.Errorf("NewDesc: expected error because: %s", desc.err)
 	}
 }
+
+func TestNewDescNilLabelValues(t *testing.T) {
+	desc := NewDesc(
+		"sample_label",
+		"sample label",
+		nil,
+		nil,
+	)
+	if desc.err != nil {
+		t.Errorf("NewDesc: unexpected error: %s", desc.err)
+	}
+}
+
+func TestNewDescWithNilLabelValues_String(t *testing.T) {
+	desc := NewDesc(
+		"sample_label",
+		"sample label",
+		nil,
+		nil,
+	)
+	if desc.String() != `Desc{fqName: "sample_label", help: "sample label", constLabels: {}, variableLabels: {}}` {
+		t.Errorf("String: unexpected output: %s", desc.String())
+	}
+}
+
+
+func TestNewInvalidDesc_String(t *testing.T) {
+	desc := NewInvalidDesc(
+		nil,
+	)
+	if desc.String() != `Desc{fqName: "", help: "", constLabels: {}, variableLabels: {}}` {
+		t.Errorf("String: unexpected output: %s", desc.String())
+	}
+}