Device change only: avoid modifying output parameter on error (#146)

Best practice is to avoid modifying output parameters if a function is failing, especially when handles are returned, this supports consistent cleanup code.  The following pattern is now supported for uDeviceOpen():

        uDeviceHandle_t device_handle = NULL;
        int32_t ret;

        if ((ret = uDeviceOpen(&gDeviceCfg, &device_handle)) != 0) {
                uPortLog("ERR: uDeviceOpen %d\n", ret);
                goto cleanup;
        }

    cleanup:

        if (device_handle != NULL) {
                uDeviceClose(device_handle, false);
                device_handle = NULL;
        }

Signed-off-by: Alon Bar-Lev <alon.barlev@gmail.com>

common/device/src/u_device.c

@@ -258,6 +258,8 @@ int32_t uDeviceOpen(const uDeviceCfg_t *pDeviceCfg, uDeviceHandle_t *pDeviceHand
     // Lock the API
     int32_t errorCode = uDeviceLock();
 
+    uDeviceHandle_t deviceHandleCandidate = NULL;
+
     if (errorCode == 0 && pDeviceCfg != NULL) {
         errorCode = uDeviceCallback("open", (void *)pDeviceCfg->deviceType, NULL);
     }
@@ -267,27 +269,27 @@ int32_t uDeviceOpen(const uDeviceCfg_t *pDeviceCfg, uDeviceHandle_t *pDeviceHand
         if ((pDeviceCfg != NULL) && (pDeviceCfg->version == 0) && (pDeviceHandle != NULL)) {
             switch (pDeviceCfg->deviceType) {
                 case U_DEVICE_TYPE_CELL:
-                    errorCode = uDevicePrivateCellAdd(pDeviceCfg, pDeviceHandle);
+                    errorCode = uDevicePrivateCellAdd(pDeviceCfg, &deviceHandleCandidate);
                     if (errorCode == 0) {
-                        U_DEVICE_INSTANCE(*pDeviceHandle)->moduleType = pDeviceCfg->deviceCfg.cfgCell.moduleType;
+                        U_DEVICE_INSTANCE(deviceHandleCandidate)->moduleType = pDeviceCfg->deviceCfg.cfgCell.moduleType;
                     }
                     break;
                 case U_DEVICE_TYPE_GNSS:
-                    errorCode = uDevicePrivateGnssAdd(pDeviceCfg, pDeviceHandle);
+                    errorCode = uDevicePrivateGnssAdd(pDeviceCfg, &deviceHandleCandidate);
                     if (errorCode == 0) {
-                        U_DEVICE_INSTANCE(*pDeviceHandle)->moduleType = pDeviceCfg->deviceCfg.cfgGnss.moduleType;
+                        U_DEVICE_INSTANCE(deviceHandleCandidate)->moduleType = pDeviceCfg->deviceCfg.cfgGnss.moduleType;
                     }
                     break;
                 case U_DEVICE_TYPE_SHORT_RANGE:
-                    errorCode = uDevicePrivateShortRangeAdd(pDeviceCfg, pDeviceHandle);
+                    errorCode = uDevicePrivateShortRangeAdd(pDeviceCfg, &deviceHandleCandidate);
                     if (errorCode == 0) {
-                        U_DEVICE_INSTANCE(*pDeviceHandle)->moduleType = pDeviceCfg->deviceCfg.cfgSho.moduleType;
+                        U_DEVICE_INSTANCE(deviceHandleCandidate)->moduleType = pDeviceCfg->deviceCfg.cfgSho.moduleType;
                     }
                     break;
                 case U_DEVICE_TYPE_SHORT_RANGE_OPEN_CPU:
-                    errorCode = uDevicePrivateShortRangeOpenCpuAdd(pDeviceCfg, pDeviceHandle);
+                    errorCode = uDevicePrivateShortRangeOpenCpuAdd(pDeviceCfg, &deviceHandleCandidate);
                     if (errorCode == 0) {
-                        U_DEVICE_INSTANCE(*pDeviceHandle)->moduleType = pDeviceCfg->deviceCfg.cfgSho.moduleType;
+                        U_DEVICE_INSTANCE(deviceHandleCandidate)->moduleType = pDeviceCfg->deviceCfg.cfgSho.moduleType;
                     }
                     break;
                 default:
@@ -299,6 +301,10 @@ int32_t uDeviceOpen(const uDeviceCfg_t *pDeviceCfg, uDeviceHandle_t *pDeviceHand
         uDeviceUnlock();
     }
 
+    if (errorCode == 0) {
+        *pDeviceHandle = deviceHandleCandidate;
+    }
+
     return errorCode;
 }