feat: added application_name

pkg/broker/adapter/postgres.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"database/sql"
 	"fmt"
+	"strings"
 	"sync"
 	"time"
 
@@ -22,6 +23,10 @@ type PostgresConfig struct {
 	MaxIdleConns    int
 	ConnMaxLifetime time.Duration
 	ConnMaxIdleTime time.Duration
+	// ApplicationName identifies this instance's pool connections in
+	// pg_stat_activity (e.g. "PGSQL_BROKER_INSTANCE1"). The LISTEN
+	// connection appends "_LISTENER" to this value.
+	ApplicationName string
 }
 
 // PostgresAdapter implements DBAdapter for PostgreSQL
@@ -170,7 +175,7 @@ func (p *PostgresAdapter) Query(ctx context.Context, query string, args ...inter
 
 // Listen starts listening on a PostgreSQL notification channel
 func (p *PostgresAdapter) Listen(ctx context.Context, channel string, handler NotificationHandler) error {
-	connStr := p.buildConnectionString()
+	connStr := p.buildConnectionStringWithAppName(p.config.ApplicationName + "_LISTENER")
 
 	reportProblem := func(ev pq.ListenerEventType, err error) {
 		if err != nil {
@@ -211,7 +216,11 @@ func (p *PostgresAdapter) Listen(ctx context.Context, channel string, handler No
 				p.logger.Info("stopping listener", "channel", channel)
 				return
 			case <-time.After(90 * time.Second):
-				SafeGo(p.logger, "listener-ping-"+channel, func() { listener.Ping() })
+				SafeGo(p.logger, "listener-ping-"+channel, func() {
+					if err := listener.Ping(); err != nil {
+						p.logger.Error("listener ping failed", "channel", channel, "error", err)
+					}
+				})
 			}
 		}
 	})
@@ -232,24 +241,42 @@ func (p *PostgresAdapter) Unlisten(ctx context.Context, channel string) error {
 	return listener.Unlisten(channel)
 }
 
-// buildConnectionString builds a PostgreSQL connection string
+// buildConnectionString builds a PostgreSQL connection string for the
+// pooled connection, using the adapter's own application name.
 func (p *PostgresAdapter) buildConnectionString() string {
+	return p.buildConnectionStringWithAppName(p.config.ApplicationName)
+}
+
+// buildConnectionStringWithAppName builds a PostgreSQL connection string
+// with the given application_name, so pooled and LISTEN connections can be
+// told apart in pg_stat_activity.
+func (p *PostgresAdapter) buildConnectionStringWithAppName(appName string) string {
 	sslMode := p.config.SSLMode
 	if sslMode == "" {
 		sslMode = "disable"
 	}
 
 	return fmt.Sprintf(
-		"host=%s port=%d user=%s password=%s dbname=%s sslmode=%s options='-c search_path=broker,public'",
+		"host=%s port=%d user=%s password=%s dbname=%s sslmode=%s application_name=%s options='-c search_path=broker,public'",
 		p.config.Host,
 		p.config.Port,
 		p.config.User,
 		p.config.Password,
 		p.config.Database,
 		sslMode,
+		quoteDSNValue(appName),
 	)
 }
 
+// quoteDSNValue escapes a value for use in a libpq keyword/value connection
+// string, single-quoting it and backslash-escaping embedded backslashes and
+// quotes per the libpq connection string format.
+func quoteDSNValue(v string) string {
+	v = strings.ReplaceAll(v, `\`, `\\`)
+	v = strings.ReplaceAll(v, `'`, `\'`)
+	return "'" + v + "'"
+}
+
 // Conn returns a single physical connection pinned out of the pool, for
 // session-scoped operations (e.g. pg_try_advisory_lock) that must survive
 // across calls and must not be silently reaped or handed to another caller