db.go

func Temporary(err error) bool {
	switch err.(type) {
	case net.Error:
		return err.(net.Error).Temporary()
	}
	if err, ok := err.(*pq.Error); ok {
		code := err.Code
		switch code.Class() {
		case "00": // Successful Completion
		case "01": // Warning
		case "02": // No Data (this is also a warning class per the SQL standard)
		case "03": // SQL Statement Not Yet Done
		case "08": // Connection Exception
			return true
		case "40": // Transaction Rollback
			// deadlock_detected
			if string(code) == "40P01" {
				return true
			}
			// could not serialize access due to concurrent update
			if string(code) == "40001" {
				return true
			}
		}
	}
	return false
}

func (db *db) Db(ctx context.Context, action action) (err error) {
	for {
		// try to perform the action
    ...
		if err = action(ctx, session); err == nil {
			return
		} else if Temporary(err) {
			logger.Debugf(ctx, "temporary problem %s", err)

			select {
			// check for cancel
			case <-ctx.Done():
				err = ctx.Err()
				logger.Errorf(ctx, "canceled %s", err)
				return

			// TODO: Randomize timeout a little?
			// wait retry interval
			case <-time.After(time.Duration(db.cfgRetryInterval)):
				logger.Debugf(ctx, "repeat")
			}
		} else {
			return
		}
	}
}

usage.go

func UseMagicLink(ctx context.Context, token string) (username string, err error) {
	action := func(ctx context.Context, tx *sql.Tx) (err error) {
		err = db.Get(ctx, tx, db.JSONB(&username),
			"SELECT func.get_magic_link($1)", token)
		if err != nil {
			logger.Errorf(ctx, "problem: %s", err)
		}
		return
	}
	err = ctx.Value("db").(db.DB).Tx(ctx, action)
	return
}