9.8. Migrating from Anjay 2.15.x

Introduction
Changes in Anjay proper
Changes in avs_commons
- Introduction of new socket option
- Refactor of PSK credential handling

9.8.1. Introduction 

While most changes since Anjay 2.15 are minor, some of them (changes to commonly used APIs such as Attribute Storage and offline mode control) are breaking. There is a change to the way the con attribute is handled in the API. Additionally, the upgrade to avs_commons 5.0 includes refactoring of the APIs related to (D)TLS PSK credentials.

9.8.2. Changes in Anjay proper 

9.8.2.1. Refactor of the Attribute Storage module 

The Attribute Storage feature is no longer a standalone module and has been moved to the library core. From the user perspective, this has the following consequences:

Explicit installation of this module in runtime is no longer necessary. The anjay_attr_storage_install() method has been removed.
The ANJAY_WITH_MODULE_ATTR_STORAGE configuration macro in anjay_config.h has been renamed to ANJAY_WITH_ATTR_STORAGE.
The WITH_MODULE_attr_storage CMake option (equivalent to the macro mentioned above) has been renamed to WITH_ATTR_STORAGE.

Additionally, the behavior of anjay_attr_storage_restore() has been changed - from now on, this function fails if supplied source stream is invalid and the Attribute Storage remains untouched. This change makes the function consistent with other anjay_*_restore() APIs.

9.8.2.2. Refactor of offline mode control API 

Since Anjay 2.4, offline mode is configurable independently per every transport. Below is a list of removed functions and counterparts that should be used:

Removed function	Counterpart
`anjay_is_offline()`	`anjay_transport_is_offline()`
`anjay_enter_offline()`	`anjay_transport_enter_offline()`
`anjay_exit_offline()`	`anjay_transport_exit_offline()`
`anjay_schedule_reconnect()`	`anjay_transport_schedule_reconnect()`

New functions should be called with transport_set argument set to ANJAY_TRANSPORT_SET_ALL to achieve the same behavior.

9.8.2.3. Addition of the con attribute to public API 

The con attribute, enabled via the ANJAY_WITH_CON_ATTR compile-time option, has been previously supported as a custom extension. Since an identical flag has been standardized as part of LwM2M TS 1.2, it has been included in the public API as part of preparations to support the new protocol version.

If you initialize anjay_dm_oi_attributes_t or anjay_dm_r_attributes_t objects manually, you may need to initialize the new con field as well, since the empty ANJAY_DM_CON_ATTR_NONE value is NOT the default zero-initialized value.

As more new attributes may be added in future versions of Anjay, it is recommended to initialize such structures with ANJAY_DM_OI_ATTRIBUTES_EMPTY or ANJAY_DM_R_ATTRIBUTES_EMPTY constants, and then fill in the attributes you actually intend to set.

9.8.2.4. Default (D)TLS version 

When the anjay_configuration_t::dtls_version field is set to AVS_NET_SSL_VERSION_DEFAULT (which includes the case of zero-initialization), Anjay 3.0 and earlier automatically mapped this setting to AVS_NET_SSL_VERSION_TLSv1_2 to ensure that (D)TLS 1.2 is used as mandated by the LwM2M specification.

This mapping has been removed in Anjay 3.1, which means that the default version configuration of the underlying (D)TLS library will be used. This has been done to automatically allow the use of newer protocols and deprecate old versions when the backend library is updated, without the need to update Anjay code. However, depending on the (D)TLS backend library used, this may lead to (D)TLS 1.1 or earlier being used if the server does not properly negotiate a higher version. Please explicitly set dtls_version to AVS_NET_SSL_VERSION_TLSv1_2 if you want to disallow this.

Please note that Mbed TLS 3.0 has dropped support for TLS 1.1 and earlier, so this change will not affect behavior with that library.

9.8.2.5. Conditional compilation for structured security credential support 

The anjay_ret_certificate_chain_info() and anjay_ret_private_key_info() APIs, as well as avs_crypto-based fields in anjay_security_instance_t, have been put under a new conditional compilation flag, ANJAY_WITH_SECURITY_STRUCTURED.

When using CMake, this flag is enabled by default if available. Otherwise, it might need to be enabled by defining ANJAY_WITH_SECURITY_STRUCTURED in anjay_config.h.

9.8.2.6. Conditional compilation for HSM support with EST 

Support for hardware security engine in the EST subsystem has been put under a new conditional compilation flag, ANJAY_WITH_EST_ENGINE_SUPPORT. NOTE: This flag is only available in commercial releases of Anjay that include the HSM engine feature. The APIs have been removed from versions that do not include this feature.

When using CMake, this flag is controlled with the WITH_EST_ENGINE_SUPPORT option and enabled by default if available and both EST and HSM features are enabled. Otherwise, it might need to be enabled by defining ANJAY_WITH_EST_ENGINE_SUPPORT in anjay_config.h.

9.8.3. Changes in avs_commons 

9.8.3.1. Introduction of new socket option 

avs_commons 4.10.1 bundled with Anjay 2.15.1 adds a new socket option key: AVS_NET_SOCKET_HAS_BUFFERED_DATA. This is used to make sure that when control is returned to the event loop, the poll() call will not stall waiting for new data that in reality has been already buffered and could be retrieved using the avs_commons APIs.

This is usually meaningful for (D)TLS connections, but for almost all simple unencrypted socket implementations, this should always return false.

This was previously achieved by always trying to receive more packets with timeout set to zero. However, it has been determined that such logic could lead to heavy blocking of the event loop in case communication with the network stack is relatively slow, e.g. on devices which implement TCP/IP sockets through modem AT commands.

If you maintain your own socket integration layer or (D)TLS integration layer, it is recommended that you add support for this option. This is not, however, a breaking change - if the option is not supported, the library will continue to use the old behavior.

9.8.3.2. Refactor of PSK credential handling 

Deprecated avs_net_psk_info_t structure has been removed. Its successor, avs_net_generic_psk_info_t, has been renamed to avs_net_psk_info_t. This change also affects avs_net_security_info_t structure which contains the latter. Implementation of accompanying avs_net_security_info_from_psk() function has also been replaced with function previously known as avs_net_security_info_from_generic_psk().

These changes are breaking for code that accesses the data.psk field of avs_net_security_info_t directly and for usages of the two changed types.