How to migrate a Shadow application from v3 to v4.

The Shadow library has been redesigned in v4 as a thread-aware library supporting asynchronous operations.

The features of the Shadow libraries in v3 and v4 are defined by the common AWS service; therefore, the two versions are similar.

Removed features

The following features which were present in v3 were removed in v4.

Shadow JSON functions
Version 3 has functions for generating and parsing JSON Shadow documents. These functions have been removed in v4 due to their high memory usage.
Workaround: snprintf can be used to generate Shadow documents. JSON parsing can be done through third-party libraries.

Functions

The following table lists equivalent API functions in v3 and v4. These functions are the API functions declared in:

Version 3	Version 4	Notes
aws_iot_shadow_init	AwsIotShadow_Init	In v3, this function initializes a single client. In v4, this function initializes the entire library.
aws_iot_shadow_free	AwsIotShadow_Cleanup	In v3, this function frees a single client. In v4, this function cleans up the entire library.
aws_iot_mqtt_connect aws_iot_shadow_disconnect	None	These functions were thin wrappers for the MQTT connect and disconnect functions. Applications using these v3 functions should replace them with calls to: IotMqtt_Connect IotMqtt_Disconnect
aws_iot_shadow_yield	None	Removed in favor of background tasks. Nothing needs to be changed in an application.
aws_iot_shadow_update	AwsIotShadow_UpdateSync	AwsIotShadow_UpdateAsync is the equivalent asynchronous function.
aws_iot_shadow_get	AwsIotShadow_GetSync	AwsIotShadow_GetAsync is the equivalent asynchronous function.
aws_iot_shadow_delete	AwsIotShadow_DeleteSync	AwsIotShadow_DeleteAsync is the equivalent asynchronous function.
aws_iot_shadow_register_delta	AwsIotShadow_SetDeltaCallback
aws_iot_shadow_reset_last_received_version aws_iot_shadow_get_last_received_version aws_iot_shadow_enable_discard_old_delta_msgs aws_iot_shadow_disable_discard_old_delta_msgs	None	Removed due to removal of JSON parsing. The application should parse received Shadow documents and decide whether to discard them based on the version key.
aws_iot_shadow_set_autoreconnect_status	None	Removed due to removal of auto-reconnect in the MQTT library.