Fix regression added in 5ad122c. Pgbouncers before 1.12 return versio…

…n string in NOTICE message. pgSCV get errNoRows error and return. Metrics about pgbouncer config stay uncollected.

Check error returned by pgbouncer. If there are no rows, just return empty answer, skip collecting metric about version and continue collecting metrics about settings.

internal/collector/pgbouncer_settings.go

@@ -4,6 +4,7 @@ import (
 	"bufio"
 	"context"
 	"fmt"
+	"github.com/jackc/pgx/v4"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/weaponry/pgscv/internal/log"
 	"github.com/weaponry/pgscv/internal/model"
@@ -66,12 +67,19 @@ func (c *pgbouncerSettingsCollector) Update(config Config, ch chan<- prometheus.
 	}
 	defer conn.Close()
 
+	// Pgbouncers before 1.12 return version as a NOTICE message (not as normal row) and it seems
+	// there is no way to extract version string. Query the version, if zero value is returned it
+	// means there is an old Pgbouncer is answered. Just skip collecting version metric and continue.
+
 	version, versionStr, err := queryPgbouncerVersion(conn)
 	if err != nil {
 		return err
 	}
+	if version != 0 {
+		ch <- c.version.newConstMetric(float64(version), versionStr)
+	}
 
-	ch <- c.version.newConstMetric(float64(version), versionStr)
+	// Query pgbouncer settings.
 
 	res, err := conn.Query(settingsQuery)
 	if err != nil {
@@ -121,7 +129,14 @@ func queryPgbouncerVersion(conn *store.DB) (int, string, error) {
 	var versionStr string
 	err := conn.Conn().QueryRow(context.Background(), versionQuery).Scan(&versionStr)
 	if err != nil {
-		return 0, "", err
+		// Pgbouncer before 1.12 returns version string as a NOTICE, and it seems there is no way to extract
+		// message text from the NOTICE. Return zero value and nil as error.
+		// Pgbouncer changelog: https://www.pgbouncer.org/changelog.html#pgbouncer-112x
+		if err == pgx.ErrNoRows {
+			return 0, "", nil
+		}
+
+		return 0, "", fmt.Errorf("read version string failed: %s", err)
 	}
 
 	re := regexp.MustCompile(`\d+\.\d+\.\d+`)