feat: support more specific prefixes in ?collect parameter

Signed-off-by: Antoine Deschênes <antoine.deschenes@linux.com>

stackdriver_exporter.go

@@ -257,12 +257,14 @@ func (h *handler) filterMetricTypePrefixes(filters map[string]bool) []string {
 	if len(filters) > 0 {
 		filteredPrefixes = nil
 		for _, prefix := range h.metricsPrefixes {
-			if filters[prefix] {
-				filteredPrefixes = append(filteredPrefixes, prefix)
+			for filter, _ := range filters {
+				if strings.HasPrefix(filter, prefix) {
+					filteredPrefixes = append(filteredPrefixes, filter)
+				}
 			}
 		}
 	}
-	return filteredPrefixes
+	return parseMetricTypePrefixes(filteredPrefixes)
 }
 
 func main() {

stackdriver_exporter_test.go

@@ -35,3 +35,29 @@ func TestParseMetricTypePrefixes(t *testing.T) {
 		t.Errorf("Metric type prefix sanitization did not produce expected output. Expected:\n%s\nGot:\n%s", expectedOutputPrefixes, outputPrefixes)
 	}
 }
+
+func TestFilterMetricTypePrefixes(t *testing.T) {
+	metricPrefixes := []string{
+		"redis.googleapis.com/stats/",
+	}
+
+	h := &handler{
+		metricsPrefixes: metricPrefixes,
+	}
+
+	inputFilters := map[string]bool{
+		"redis.googleapis.com/stats/memory/usage":       true,
+		"redis.googleapis.com/stats/memory/usage_ratio": true,
+		"redis.googleapis.com":                          true,
+	}
+
+	expectedOutputPrefixes := []string{
+		"redis.googleapis.com/stats/memory/usage",
+	}
+
+	outputPrefixes := h.filterMetricTypePrefixes(inputFilters)
+
+	if !reflect.DeepEqual(outputPrefixes, expectedOutputPrefixes) {
+		t.Errorf("filterMetricTypePrefixes did not produce expected output. Expected:\n%s\nGot:\n%s", expectedOutputPrefixes, outputPrefixes)
+	}
+}