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AWS IoT Device Shadow

The AWS IoT Device Shadow library enables you to store and retrieve the current state (the “shadow”) of every registered device. The device’s shadow is a persistent, virtual representation of your device that you can interact with from AWS IoT Core even if the device is offline. The device state is captured as its “shadow” within a JSON document. The device can send commands over MQTT or HTTP to update its latest state. Each device’s shadow is uniquely identified by the name of the corresponding “thing”, a representation of a specific device or logical entity on the AWS Cloud. See Managing Devices with AWS IoT for more information. More details about AWS IoT Device Shadow can be found in AWS IoT documentation. This library is distributed under the MIT Open Source License.

This library has gone through code quality checks including verification that no function has a GNU Complexity score over 8, and checks against deviations from mandatory rules in the MISRA coding standard. Deviations from the MISRA C:2012 guidelines are documented under MISRA Deviations. This library has also undergone both static code analysis from Coverity static analysis, and validation of memory safety and proof of functional correctness through the CBMC automated reasoning tool.

See memory requirements for this library here.

AWS IoT Device Shadow Config File

The AWS IoT Device Shadow library exposes configuration macros that are required for building the library. A list of all the configurations and their default values are defined in shadow_config_defaults.h. To provide custom values for the configuration macros, a custom config file named shadow_config.h can be provided by the user application to the library.

By default, a shadow_config.h custom config is required to build the library. To disable this requirement and build the library with default configuration values, provide SHADOW_DO_NOT_USE_CUSTOM_CONFIG as a compile time preprocessor macro.

Building the Library

The shadowFilePaths.cmake file contains the information of all source files and the header include path required to build the AWS IoT Device Shadow library.

As mentioned in the previous section, either a custom config file (i.e. shadow_config.h) OR the SHADOW_DO_NOT_USE_CUSTOM_CONFIG macro needs to be provided to build the AWS IoT Device Shadow library.

For a CMake example of building the AWS IoT Device Shadow library with the shadowFilePaths.cmake file, refer to the coverity_analysis library target in test/CMakeLists.txt file.

Building Unit Tests

Checkout CMock Submodule

By default, the submodules in this repository are configured with update=none in .gitmodules to avoid increasing clone time and disk space usage of other repositories (like amazon-freertos that submodules this repository).

To build unit tests, the submodule dependency of CMock is required. Use the following command to clone the submodule:

git submodule update --checkout --init --recursive --test/unit-test/CMock

Platform Prerequisites

  • For building the library, CMake 3.13.0 or later and a C90 compiler.
  • For running unit tests, Ruby 2.0.0 or later is additionally required for the CMock test framework (that we use).
  • For running the coverage target, gcov and lcov are additionally required.

Steps to build unit tests

  1. Go to the root directory of this repository. (Make sure that the CMock submodule is cloned as described above.)

  2. Run the cmake command: cmake -S test -B build

  3. Run this command to build the library and unit tests: make -C build all

  4. The generated test executables will be present in build/bin/tests folder.

  5. Run cd build && ctest to execute all tests and view the test run summary.

Reference examples

Please refer to the demos of the AWS IoT Device Shadow library in the following locations for reference examples on POSIX and FreeRTOS platforms:

Platform Location Transport Interface Implementation
(for coreMQTT stack)
POSIX AWS IoT Device SDK for Embedded C POSIX sockets for TCP/IP and OpenSSL for TLS stack
FreeRTOS FreeRTOS/FreeRTOS FreeRTOS+TCP for TCP/IP and mbedTLS for TLS stack
FreeRTOS FreeRTOS AWS Reference Integrations Based on Secure Sockets Abstraction

Generating documentation

The Doxygen references were created using Doxygen version 1.8.20. To generate the Doxygen pages, please run the following command from the root of this repository:

doxygen docs/doxygen/config.doxyfile