Processing Config#

Now that our application has its config stored in the ConfigState struct, we can use it to perform the application logic. While in the case of greeter the app logic is trivial, in real-world applications it might be more complex.

greeter/app.go

func (a *App) Start(ctx context.Context) {
    go a.receiveConfigNotifications(ctx)

    for {
        select {
        case <-a.configReceivedCh:
            a.logger.Info().Msg("Received full config")

            a.processConfig(ctx)

            a.updateState(ctx)

        case <-ctx.Done():
            a.stop()
            return
        }
    }
}

Greeter' core app logic is to calculate the greeting message that consists of a name and the last-booted-time of SR Linux system.

greeter/config.go

func (a *App) processConfig(ctx context.Context) {
    if a.configState.Name == "" {
        a.logger.Info().Msg("No name configured, deleting state")
        a.configState = &ConfigState{}

        return
    }

    uptime, err := a.getUptime(ctx)
    if err != nil {
        a.logger.Info().Msgf("failed to get uptime: %v", err)
        return
    }

    a.configState.Greeting = "👋 Hi " + a.configState.Name +
        ", SR Linux was last booted at " + uptime
}

The processConfig function first checks if the name field is not an empty string. If it is an empty, it means the config name was either deleted or not configured at all. In this case we set the ConfigState struct to an empty value which should result in the empty state in the SR Linux data store.

If name is set we proceed with calculating the greeting message. Remember that we need to retrieve the last-booted-time from the SR Linux system. We do this by calling the getUptime function.

greeter/app.go

func (a *App) getUptime(ctx context.Context) (string, error) {
    a.logger.Info().Msg("Fetching SR Linux uptime value")

    // create a GetRequest
    getReq, err := api.NewGetRequest(
        api.Path("/system/information/last-booted"),
        api.Encoding("proto"))
    if err != nil {
        return "", err
    }

    getResp, err := a.gNMITarget.Get(ctx, getReq)
    if err != nil {
        return "", err
    }

    a.logger.Info().Msgf("GetResponse: %+v", getResp)

    return getResp.Notification[0].Update[0].GetVal().GetStringVal(), nil
}

Earlier on, we created the gNMI Target and now it is time to use it. We use the gNMI Get request to retrieve the /system/information/last-booted value from the SR Linux. The Get function returns a gNMI Get Response from which we extract the last-booted value as string.

Now that we have the name value retrieved from the configuration notification and last-booted value fetched via gNMI, we can compose the greeting message:

greeter/config.go

    a.configState.Greeting = "👋 Hi " + a.configState.Name +
        ", SR Linux was last booted at " + uptime

With our ConfigState struct populated with the name and greeting values we have only one step left: to update the state datastore with them.

Processing Config#

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