azure: Rework connection status reporting

Network status was not managed properly in azure client glue code:
- wait_for_event was unblocking for any event triggered not the
specific event required as input of the function. This causes issues
when the network stack trigger spurious event NETWORK_UP events.
- The state of the network was read from the events set. Unfortunatelly,
this can cause issues when the events are NETWORK_UP and NETWORK_DOWN
are triggered and the event not read in between.

To solve these issues, the following solutions have been implemented:
- the state of the network is stored in a local variable and updated
whenever NETWORK_UP or NETWORK_DOWN are received. This filters out
spurious events from the network stack. An event
AZURE_NETWORK_CHANGE_FLAG is triggered to inform the azure code
that the network state has changed.
- The function wait_for_event only waits for a specific event instead of
all events.

Signed-off-by: Vincent Coubard <vincent.coubard@arm.com>

components/Azure-SDK/platform/src/platform_openiot.c

@@ -11,6 +11,7 @@
 #include "iotsdk/ip_network_api.h"
 
 #include <inttypes.h>
+#include <stdbool.h>
 #include <stdio.h>
 #include <time.h>
 
@@ -18,36 +19,25 @@
 #include "iot_ntp_client.h"
 #endif // IOTSDK_AZURE_SDK_NTP_TIME
 
-#define AZURE_NETWORK_UP_FLAG   0x00000001U
-#define AZURE_NETWORK_DOWN_FLAG 0x00000002U
-#define AZURE_TIME_READY_FLAG   0x00000004U
-#define AZURE_ALL_EVENTS_FLAGS  (AZURE_NETWORK_UP_FLAG | AZURE_NETWORK_DOWN_FLAG | AZURE_TIME_READY_FLAG)
+#define AZURE_NETWORK_CHANGE_FLAG 0x00000001U
+#define AZURE_TIME_READY_FLAG     0x00000002U
 
 #define AZURE_EVENT_TIMEOUT 15000
 
-static osEventFlagsId_t event_flags_id;
+static osEventFlagsId_t event_flags_id = NULL;
+static osMutexId_t network_state_lock = NULL;
+static bool network_up = false;
 
 /** Wait for specific platform event and check error */
 static int wait_for_event(uint32_t event)
 {
-    int res = 0;
-    int ret = osEventFlagsWait(event_flags_id, AZURE_ALL_EVENTS_FLAGS, osFlagsWaitAny, AZURE_EVENT_TIMEOUT);
+    int ret = osEventFlagsWait(event_flags_id, event, osFlagsWaitAny, AZURE_EVENT_TIMEOUT);
     if (ret < 0) {
         LogError("osEventFlagsWait failed %d", ret);
         return MU_FAILURE;
     }
 
-    if (!(ret & event)) {
-        res = MU_FAILURE;
-    }
-
-    ret = osEventFlagsClear(event_flags_id, AZURE_ALL_EVENTS_FLAGS);
-    if (ret < 0) {
-        LogError("osEventFlagsClear failed %d", ret);
-        return MU_FAILURE;
-    }
-
-    return res;
+    return 0;
 }
 
 /** This callback is called by the ip network task. It translates from a network event code
@@ -57,11 +47,48 @@ static int wait_for_event(uint32_t event)
  */
 static void network_state_callback(network_state_callback_event_t event)
 {
-    uint32_t event_flag = (event == NETWORK_UP) ? AZURE_NETWORK_UP_FLAG : AZURE_NETWORK_DOWN_FLAG;
-    int res = osEventFlagsSet(event_flags_id, event_flag);
-    if (res < 0) {
-        LogError("osEventFlagsSet failed %d", res);
+    int res = osMutexAcquire(network_state_lock, osWaitForever);
+    if (res != osOK) {
+        LogError("osMutexAcquire failed %d", res);
+        return;
+    }
+
+    bool latest_network_up = (event == NETWORK_UP);
+    if (latest_network_up != network_up) {
+        LogInfo("network state changed");
+        network_up = latest_network_up;
+        res = osEventFlagsSet(event_flags_id, AZURE_NETWORK_CHANGE_FLAG);
+        if (res < 0) {
+            LogError("osEventFlagsSet failed %d", res);
+        }
+    }
+
+    res = osMutexRelease(network_state_lock);
+    if (res != osOK) {
+        LogError("osMutexRelease failed %d", res);
+        return;
+    }
+}
+
+static bool is_network_up()
+{
+    int result = false;
+
+    int res = osMutexAcquire(network_state_lock, osWaitForever);
+    if (res != osOK) {
+        LogError("osMutexAcquire failed %d", res);
+        goto exit;
     }
+
+    result = network_up;
+
+    res = osMutexRelease(network_state_lock);
+    if (res != osOK) {
+        LogError("osMutexRelease failed %d", res);
+    }
+
+exit:
+    return result;
 }
 
 #ifdef IOTSDK_AZURE_SDK_NTP_TIME
@@ -89,6 +116,14 @@ int platform_init(void)
         return MU_FAILURE;
     }
 
+    // The state of the network should be updated by the network task started below.
+    network_up = false;
+    network_state_lock = osMutexNew(NULL);
+    if (network_state_lock == NULL) {
+        LogError("Create mutex failed");
+        return MU_FAILURE;
+    }
+
 #ifdef IOTSDK_AZURE_SDK_NTP_TIME
     res = iotNtpClientInit(NULL);
     if (res != IOT_NTP_CLIENT_OK) {
@@ -103,10 +138,12 @@ int platform_init(void)
         goto cleanup;
     }
 
-    res = wait_for_event(AZURE_NETWORK_UP_FLAG);
-    if (res != 0) {
-        LogError("Network not up");
-        goto cleanup;
+    if (!is_network_up()) {
+        res = wait_for_event(AZURE_NETWORK_CHANGE_FLAG);
+        if (res != 0 || !is_network_up()) {
+            LogError("Network not up");
+            goto cleanup;
+        }
     }
 
 #ifdef IOTSDK_AZURE_SDK_NTP_TIME
@@ -154,6 +191,11 @@ void platform_deinit(void)
     }
 #endif // IOTSDK_AZURE_SDK_NTP_TIME
 
+    res = osMutexDelete(network_state_lock);
+    if (res != osOK) {
+        LogError("Delete event flags failed %d", res);
+    }
+
     res = osEventFlagsDelete(event_flags_id);
     if (res != osOK) {
         LogError("Delete event flags failed %d", res);