System events for cloud/network connection state changes

[sergeuz]

This PR closes #977 by enabling generation of the system events for cloud and network connection state changes.

I'm not sure how to test this functionality automatically, here is the application I was playing with during my manual testing:

#include "application.h"

SYSTEM_MODE(MANUAL);

#define CHECK_STATE(data, state) \
        if ((data) == (state)) { \
            Log.info("Event: %s", #state); \
            return; \
        }

namespace {

void connectionStateChanged(system_event_t event, int data) {
    if (event == network_status) {
        CHECK_STATE(data, network_status_powering_off);
        CHECK_STATE(data, network_status_off);
        CHECK_STATE(data, network_status_powering_on);
        CHECK_STATE(data, network_status_on);
        CHECK_STATE(data, network_status_connecting);
        CHECK_STATE(data, network_status_connected);
        CHECK_STATE(data, network_status_disconnecting);
        CHECK_STATE(data, network_status_disconnected);
    } else if (event == cloud_status) {
        CHECK_STATE(data, cloud_status_disconnected);
        CHECK_STATE(data, cloud_status_connecting);
        CHECK_STATE(data, cloud_status_connected);
        CHECK_STATE(data, cloud_status_disconnecting);
    }
}

SerialLogHandler logHandler(LOG_LEVEL_WARN, {
    { "app", LOG_LEVEL_ALL }
});

uint32_t t = 0;
int step = 0;

} // namespace

void setup() {
    System.on(network_status | cloud_status, connectionStateChanged);
}

void loop() {
    if (step && millis() - t < 3000) {
        return;
    }
    switch (++step) {
    case 1: {
        Log.info("-> WiFi.on()");
        WiFi.on();
        break;
    }
    case 2: {
        Log.info("-> WiFi.connect()");
        WiFi.connect();
        break;
    }
    case 3: {
        Log.info("-> Particle.connect()");
        Particle.connect();
        break;
    }
    case 4: {
        Log.info("-> Particle.disconnect()");
        Particle.disconnect();
        break;
    }
    case 5: {
        Log.info("-> WiFi.disconnect()");
        WiFi.disconnect(); // Seems to cause automatic reconnection
        break;
    }
    case 6: {
        Log.info("-> WiFi.off()");
        WiFi.off();
        break;
    }
    default:
        break;
    }
    t = millis();
}

Possible logging output:

0000000004 [app] INFO: -> WiFi.on()
0000000004 [app] INFO: Event: network_status_powering_on
0000000422 [app] INFO: Event: network_status_on
0000003422 [app] INFO: -> WiFi.connect()
0000003422 [app] INFO: Event: network_status_connecting
0000004835 [app] INFO: Event: network_status_connected
0000007835 [app] INFO: -> Particle.connect()
0000007835 [app] INFO: Event: cloud_status_connecting
0000009129 [app] INFO: Event: cloud_status_connected
0000010835 [app] INFO: -> Particle.disconnect()
0000010835 [app] INFO: Event: cloud_status_disconnecting
0000010842 [app] INFO: Event: cloud_status_disconnected
0000013835 [app] INFO: -> WiFi.disconnect()
0000013835 [app] INFO: Event: network_status_disconnecting
0000013844 [app] INFO: Event: network_status_disconnected
0000016852 [app] INFO: -> WiFi.off()
0000016852 [app] INFO: Event: network_status_powering_off
0000016862 [app] INFO: Event: network_status_off

Note that in the current implementation cloud_status_connected event is generated only after a successful handshake, and no intermediate events are defined for TCP connection state. Also, network_status_connected event is generated only after device's network is successfully configured via DHCP (in case of dynamic IP configuration).

---

Doneness:

• Contributor has signed CLA
• Problem and Solution clearly stated
• Code peer reviewed
• API tests compiled
• Run unit/integration/application tests on device
• Add documentation
• Add to CHANGELOG.md after merging (add links to docs and issues)

Enhancements

• Added System events for cloud/network connection state changes [Closes #977]