explicit check for "use of closed network connection" suffix (#3408)

many libraries create this error themselves, & check this way,
as historically go did not expose net.ErrClosed type

Author: serprex

flow/alerting/alerting.go

@@ -454,7 +454,8 @@ func (a *Alerter) logFlowErrorInternal(
 ) {
 	logger := internal.LoggerFromCtx(ctx)
 	inErrWithStack := fmt.Sprintf("%+v", inErr)
-	loggerFunc(inErr.Error(), slog.String("stack", inErrWithStack))
+	errError := inErr.Error()
+	loggerFunc(errError, slog.String("stack", inErrWithStack))
 	if _, err := a.CatalogPool.Exec(
 		ctx, "INSERT INTO peerdb_stats.flow_errors(flow_name,error_message,error_type) VALUES($1,$2,$3)",
 		flowName, inErrWithStack, errorType.String(),
@@ -470,7 +471,7 @@ func (a *Alerter) logFlowErrorInternal(
 	if errors.Is(inErr, io.EOF) || errors.Is(inErr, io.ErrUnexpectedEOF) {
 		tags = append(tags, string(shared.ErrTypeEOF))
 	}
-	if errors.Is(inErr, net.ErrClosed) {
+	if errors.Is(inErr, net.ErrClosed) || strings.HasSuffix(errError, "use of closed network connection") {
 		tags = append(tags, string(shared.ErrTypeClosed))
 	}
 	var pgErr *pgconn.PgError
@@ -502,7 +503,7 @@ func (a *Alerter) logFlowErrorInternal(
 	if internal.PeerDBTelemetrySenderSendErrorAlertsEnabled() {
 		a.sendTelemetryMessage(ctx, logger, flowName, inErrWithStack, telemetry.ERROR, tags...)
 	}
-	loggerFunc(fmt.Sprintf("Emitting error/warning metric: '%s'", inErr.Error()),
+	loggerFunc(fmt.Sprintf("Emitting error/warning metric: '%s'", errError),
 		slog.Any("error", inErr),
 		slog.Any("errorClass", errorClass),
 		slog.Any("errorInfo", errInfo),

flow/alerting/classifier.go

@@ -539,7 +539,7 @@ func GetErrorClass(ctx context.Context, err error) (ErrorClass, ErrorInfo) {
 		}
 	}
 
-	if errors.Is(err, net.ErrClosed) {
+	if errors.Is(err, net.ErrClosed) || strings.HasSuffix(err.Error(), "use of closed network connection") {
 		return ErrorIgnoreConnTemporary, ErrorInfo{
 			Source: ErrorSourceNet,
 			Code:   "net.ErrClosed",