9.8. Migrating from Anjay 2.15.x

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.

9.8.2.7. Persistence of disabled servers

Core Persistence API (anjay_new_from_core_persistence(), anjay_delete_with_core_persistence()) now also persists disabled servers (either by execution of /1/x/4 or call to function from anjay_disable_server*() family) and the time at which the client shall reconnect them. Previously those disabled servers weren’t persisted at all and freshly initialized client was automatically connecting to them without any regard for specified timeout.

9.8.3. Changes in avs_coap

9.8.3.1. Changed flow of cancelling observations in case of errors

CoAP observations are implicitly cancelled if a notification bearing a 4.xx or 5.xx error code is delivered, or if an attempt to deliver a notification times out.

In Anjay 3.4.x and earlier, this cancellation (which involves calling the avs_coap_observe_cancel_handler_t callback) was performed before calling the avs_coap_delivery_status_handler_t callback for the specific notification. Since Anjay 3.5.0, this order is reversed, so any code that relies on this logic may break.

This change is only relevant if you are using avs_coap APIs directly (e.g. when communicating over raw CoAP protocol) and in case of notifications intended to be delivered as confirmable. The LwM2M Observe/Notify implementation in Anjay has been updated accordingly.

9.8.4. Changes in avs_commons

9.8.4.1. 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.

9.8.4.2. 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.

9.8.4.3. Refactor of time handling in avs_sched and avs_coap

It is now enforced more strictly that time-based events shall happen when the clock reaches at least the expected value. Previously, the tasks scheduled via avs_sched were executed only when the clock reached a value later than the scheduled job execution time.

This change will have no impact on your code if your platform has enough clock resolution so that two subsequent calls to avs_time_real_now() or avs_time_monotonic_now() will always return different values. As a rule of thumb, this should be the case if your clock has a resolution no worse than about 1-2 orders of magnitude smaller than the CPU clock. For example, for a 100 MHz CPU, a clock resolution of around 100-1000 ns (i.e., 1-10 MHz) should be sufficient, depending on the specific architecture.

If your clock has a lower resolution, you may observe the following changes:

• anjay_sched_run() is now properly guaranteed to execute at least one job if the time reported by anjay_sched_time_to_next() passed. Previously this could require waiting for another change of the numerical value of the clock, which could cause undesirable active waiting in the event loop. This is the motivating factor in introducing these changes.

• Jobs scheduled using AVS_SCHED_NOW() during an execution of anjay_sched_run() before the numerical value of the clock changes, will be executed during the same run. The previous behavior more strictly enforced the policy to not execute such jobs in the same run.

If you are scheduling custom jobs through the avs_sched module, you may want or need to modify their logic accordingly to accommodate for these changes. In most typical use cases, no changes are expected to be necessary.

9.8.4.4. Removal of avs_unit_memstream

avs_unit_memstream was a specific implementation of avs_stream_t within the avs_unit module that implemented a simple FIFO stream in a fixed-size memory area.

This feature has been removed. Instead, you can use an avs_stream_inbuf/avs_stream_outbuf pair, or an avs_stream_membuf object.