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SDK for Connecting to AWS IoT From A Device using Embedded C

AWS IoT Device SDK for Embedded C

Overview

The AWS IoT Device SDK for Embedded C (C-SDK) is a collection of C source files under the MIT open source license that can be used in embedded applications to securely connect IoT devices to AWS IoT Core. It contains MQTT client, HTTP client, JSON Parser, AWS IoT Device Shadow, AWS IoT Jobs, and AWS IoT Device Defender libraries. This SDK is distributed in source form, and can be built into customer firmware along with application code, other libraries and an operating system (OS) of your choice. These libraries are only dependent on standard C libraries, so they can be ported to various OS's - from embedded Real Time Operating Systems (RTOS) to Linux/Mac/Windows. You can find sample usage of C-SDK libraries on POSIX systems using OpenSSL (e.g. Linux demos in this repository), and on FreeRTOS using mbedTLS (e.g. FreeRTOS demos in FreeRTOS repository).

For the latest release of C-SDK, please see the section for Releases and Documentation.

C-SDK includes libraries that are part of the FreeRTOS 202012.01 LTS release. Learn more about the FreeRTOS 202012.01 LTS libraries by clicking here.

License

The C-SDK libraries are licensed under the MIT open source license.

Features

C-SDK simplifies access to various AWS IoT services. C-SDK has been tested to work with AWS IoT Core and an open source MQTT broker to ensure interoperability. The AWS IoT Device Shadow, AWS IoT Jobs, and AWS IoT Device Defender libraries are flexible to work with any MQTT client and JSON parser. The MQTT client and JSON parser libraries are offered as choices without being tightly coupled with the rest of the SDK. C-SDK contains the following libraries:

coreMQTT

The coreMQTT library provides the ability to establish an MQTT connection with a broker over a customer-implemented transport layer, which can either be a secure channel like a TLS session (mutually authenticated or server-only authentication) or a non-secure channel like a plaintext TCP connection. This MQTT connection can be used for performing publish operations to MQTT topics and subscribing to MQTT topics. The library provides a mechanism to register customer-defined callbacks for receiving incoming PUBLISH, acknowledgement and keep-alive response events from the broker. The library has been refactored for memory optimization and is compliant with the MQTT 3.1.1 standard. It has no dependencies on any additional libraries other than the standard C library, a customer-implemented network transport interface, and optionally a customer-implemented platform time function. The refactored design embraces different use-cases, ranging from resource-constrained platforms using only QoS 0 MQTT PUBLISH messages to resource-rich platforms using QoS 2 MQTT PUBLISH over TLS connections.

See memory requirements for the latest release here.

coreHTTP

The coreHTTP library provides the ability to establish an HTTP connection with a server over a customer-implemented transport layer, which can either be a secure channel like a TLS session (mutually authenticated or server-only authentication) or a non-secure channel like a plaintext TCP connection. The HTTP connection can be used to make "GET" (include range requests), "PUT", "POST" and "HEAD" requests. The library provides a mechanism to register a customer-defined callback for receiving parsed header fields in an HTTP response. The library has been refactored for memory optimization, and is a client implementation of a subset of the HTTP/1.1 standard.

See memory requirements for the latest release here.

coreJSON

The coreJSON library is a JSON parser that strictly enforces the ECMA-404 JSON standard. It provides a function to validate a JSON document, and a function to search for a key and return its value. A search can descend into nested structures using a compound query key. A JSON document validation also checks for illegal UTF8 encodings and illegal Unicode escape sequences.

See memory requirements for the latest release here.

corePKCS11

The corePKCS11 library is an implementation of the PKCS #11 interface (API) that makes it easier to develop applications that rely on cryptographic operations. Only a subset of the PKCS #11 v2.4 standard has been implemented, with a focus on operations involving asymmetric keys, random number generation, and hashing.

The Cryptoki or PKCS #11 standard defines a platform-independent API to manage and use cryptographic tokens. The name, "PKCS #11", is used interchangeably to refer to the API itself and the standard which defines it.

The PKCS #11 API is useful for writing software without taking a dependency on any particular implementation or hardware. By writing against the PKCS #11 standard interface, code can be used interchangeably with multiple algorithms, implementations and hardware.

Generally vendors for secure cryptoprocessors such as Trusted Platform Module (TPM), Hardware Security Module (HSM), Secure Element, or any other type of secure hardware enclave, distribute a PKCS #11 implementation with the hardware. The purpose of corePKCS11 mock is therefore to provide a PKCS #11 implementation that allows for rapid prototyping and development before switching to a cryptoprocessor specific PKCS #11 implementation in production devices.

Since the PKCS #11 interface is defined as part of the PKCS #11 specification replacing corePKCS11 with another implementation should require little porting effort, as the interface will not change. The system tests distributed in corePKCS11 repository can be leveraged to verify the behavior of a different implementation is similar to corePKCS11.

See memory requirements for the latest release here.

AWS IoT Device Shadow

The AWS IoT Device Shadow library enables you to store and retrieve the current state one or more shadows of every registered device. A 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 in its "shadow" is represented as a JSON document. The device can send commands over MQTT to get, update and delete its latest state as well as receive notifications over MQTT about changes in its state. The device’s shadow(s) are 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 on IoT "thing". This library supports named shadows, a feature of the AWS IoT Device Shadow service that allows you to create multiple shadows for a single IoT device. More details about AWS IoT Device Shadow can be found in AWS IoT documentation.

The AWS IoT Device Shadow library has no dependencies on additional libraries other than the standard C library. It also doesn’t have any platform dependencies, such as threading or synchronization. It can be used with any MQTT library and any JSON library (see demos with coreMQTT and coreJSON).

See memory requirements for the latest release here.

AWS IoT Jobs

The AWS IoT Jobs library enables you to interact with the AWS IoT Jobs service which notifies one or more connected devices of a pending “Job”. A Job can be used to manage your fleet of devices, update firmware and security certificates on your devices, or perform administrative tasks such as restarting devices and performing diagnostics. For documentation of the service, please see the AWS IoT Developer Guide. Interactions with the Jobs service use the MQTT protocol. This library provides an API to compose and recognize the MQTT topic strings used by the Jobs service.

The AWS IoT Jobs library has no dependencies on additional libraries other than the standard C library. It also doesn’t have any platform dependencies, such as threading or synchronization. It can be used with any MQTT library and any JSON library (see demos with libmosquitto and coreJSON).

See memory requirements for the latest release here.

AWS IoT Device Defender

The AWS IoT Device Defender library enables you to interact with the AWS IoT Device Defender service to continuously monitor security metrics from devices for deviations from what you have defined as appropriate behavior for each device. If something doesn’t look right, AWS IoT Device Defender sends out an alert so you can take action to remediate the issue. More details about Device Defender can be found in AWS IoT Device Defender documentation. This library supports custom metrics, a feature that helps you monitor operational health metrics that are unique to your fleet or use case. For example, you can define a new metric to monitor the memory usage or CPU usage on your devices.

The AWS IoT Device Defender library has no dependencies on additional libraries other than the standard C library. It also doesn’t have any platform dependencies, such as threading or synchronization. It can be used with any MQTT library and any JSON library (see demos with coreMQTT and coreJSON).

See memory requirements for the latest release here.

AWS IoT Over-the-air Update

The AWS IoT Over-the-air Update (OTA) library enables you to manage the notification of a newly available update, download the update, and perform cryptographic verification of the firmware update. Using the OTA library, you can logically separate firmware updates from the application running on your devices. You can also use the library to send other files (e.g. images, certificates) to one or more devices registered with AWS IoT. More details about OTA library can be found in AWS IoT Over-the-air Update documentation.

The AWS IoT Over-the-air Update library has a dependency on coreJSON for parsing of JSON job document and tinyCBOR for decoding encoded data streams, other than the standard C library. It can be used with any MQTT library, HTTP library, and operating system (e.g. Linux, FreeRTOS) (see demos with coreMQTT and coreHTTP over Linux).

See memory requirements for the latest release here.

AWS IoT Fleet Provisioning

The AWS IoT Fleet Provisioning library enables you to interact with the AWS IoT Fleet Provisioning MQTT APIs in order to provison IoT devices without preexisting device certificates. With AWS IoT Fleet Provisioning, devices can securely receive unique device certificates from AWS IoT when they connect for the first time. For an overview of all provisioning options offered by AWS IoT, see device provisioning documentation. For details about Fleet Provisioning, refer to the AWS IoT Fleet Provisioning documentation.

See memory requirements for the latest release here.

AWS SigV4

The AWS SigV4 library enables you to sign HTTP requests with Signature Version 4 Signing Process. Signature Version 4 (SigV4) is the process to add authentication information to HTTP requests to AWS services. For security, most requests to AWS must be signed with an access key. The access key consists of an access key ID and secret access key.

See memory requirements for the latest release here.

backoffAlgorithm

The backoffAlgorithm library is a utility library to calculate backoff period using an exponential backoff with jitter algorithm for retrying network operations (like failed network connection with server). This library uses the "Full Jitter" strategy for the exponential backoff with jitter algorithm. More information about the algorithm can be seen in the Exponential Backoff and Jitter AWS blog.

Exponential backoff with jitter is typically used when retrying a failed connection or network request to the server. An exponential backoff with jitter helps to mitigate the failed network operations with servers, that are caused due to network congestion or high load on the server, by spreading out retry requests across multiple devices attempting network operations. Besides, in an environment with poor connectivity, a client can get disconnected at any time. A backoff strategy helps the client to conserve battery by not repeatedly attempting reconnections when they are unlikely to succeed.

The backoffAlgorithm library has no dependencies on libraries other than the standard C library.

See memory requirements for the latest release here.

Sending metrics to AWS IoT

When establishing a connection with AWS IoT, users can optionally report the Operating System, Hardware Platform and MQTT client version information of their device to AWS. This information can help AWS IoT provide faster issue resolution and technical support. If users want to report this information, they can send a specially formatted string (see below) in the username field of the MQTT CONNECT packet.

Format

The format of the username string with metrics is:

<Actual_Username>?SDK=<OS_Name>&Version=<OS_Version>&Platform=<Hardware_Platform>&MQTTLib=<MQTT_Library_name>@<MQTT_Library_version>

Where

is the actual username used for authentication, if username and password are used for authentication. When username and password based authentication is not used, this is an empty value.
is the Operating System the application is running on (e.g. Ubuntu)
is the version number of the Operating System (e.g. 20.10)
is the Hardware Platform the application is running on (e.g. RaspberryPi)
is the MQTT Client library being used (e.g. coreMQTT)
is the version of the MQTT Client library being used (e.g. 1.1.0)

Example

Actual_Username = “iotuser”, OS_Name = Ubuntu, OS_Version = 20.10, Hardware_Platform_Name = RaspberryPi, MQTT_Library_Name = coremqtt, MQTT_Library_version = 1.1.0. If username is not used, then “iotuser” can be removed.

/* Username string:
 * iotuser?SDK=Ubuntu&Version=20.10&Platform=RaspberryPi&MQTTLib=coremqtt@1.1.0
 */

#define OS_NAME                   "Ubuntu"
#define OS_VERSION                "20.10"
#define HARDWARE_PLATFORM_NAME    "RaspberryPi"
#define MQTT_LIB                  "coremqtt@1.1.0"

#define USERNAME_STRING           "iotuser?SDK=" OS_NAME "&Version=" OS_VERSION "&Platform=" HARDWARE_PLATFORM_NAME "&MQTTLib=" MQTT_LIB
#define USERNAME_STRING_LENGTH    ( ( uint16_t ) ( sizeof( USERNAME_STRING ) - 1 ) )

MQTTConnectInfo_t connectInfo;
connectInfo.pUserName = USERNAME_STRING;
connectInfo.userNameLength = USERNAME_STRING_LENGTH;
mqttStatus = MQTT_Connect( pMqttContext, &connectInfo, NULL, CONNACK_RECV_TIMEOUT_MS, pSessionPresent );

Versioning

C-SDK releases will now follow a date based versioning scheme with the format YYYYMM.NN, where:

Y represents the year.
M represents the month.
N represents the release order within the designated month (00 being the first release).

For example, a second release in June 2021 would be 202106.01. Although the SDK releases have moved to date-based versioning, each library within the SDK will still retain semantic versioning. In semantic versioning, the version number itself (X.Y.Z) indicates whether the release is a major, minor, or point release. You can use the semantic version of a library to assess the scope and impact of a new release on your application.

Releases and Documentation

All of the released versions of the C-SDK libraries are available as git tags. For example, the last release of the v3 SDK version is available at tag 3.1.2.

202108.00

API documentation of 202108.00 release

This release introduces the refactored AWS IoT Fleet Provisioning library and the new AWS SigV4 library.

Additionally, this release brings minor version updates in the AWS IoT Over-the-Air Update and corePKCS11 libraries.

202103.00

API documentation of 202103.00 release

This release includes a major update to the APIs of the AWS IoT Over-the-air Update library.

Additionally, AWS IoT Device Shadow library introduces a minor update by adding support for named shadow, a feature of the AWS IoT Device Shadow service that allows you to create multiple shadows for a single IoT device. AWS IoT Jobs library introduces a minor update by introducing macros for $next job ID and compile-time generation of topic strings. AWS IoT Device Defender library introduces a minor update that adds macros to API for custom metrics feature of AWS IoT Device Defender service.

corePKCS11 also introduces a patch update by removing the pkcs11configPAL_DESTROY_SUPPORTED config and mbedTLS platform abstraction layer of DestroyObject. Lastly, no code changes are introduced for backoffAlgorithm, coreHTTP, coreMQTT, and coreJSON; however, patch updates are made to improve documentation and CI.

202012.01

API documentation of 202012.01 release

This release includes AWS IoT Over-the-air Update(Release Candidate), backoffAlgorithm, and PKCS #11 libraries. Additionally, there is a major update to the coreJSON and coreHTTP APIs. All libraries continue to undergo code quality checks (e.g. MISRA-C compliance), and Coverity static analysis. In addition, all libraries except AWS IoT Over-the-air Update and backoffAlgorithm undergo validation of memory safety with the C Bounded Model Checker (CBMC) automated reasoning tool.

202011.00

API documentation of 202011.00 release

This release includes refactored HTTP client, AWS IoT Device Defender, and AWS IoT Jobs libraries. Additionally, there is a major update to the coreJSON API. All libraries continue to undergo code quality checks (e.g. MISRA-C compliance), Coverity static analysis, and validation of memory safety with the C Bounded Model Checker (CBMC) automated reasoning tool.

202009.00

API documentation of 202009.00 release

This release includes refactored MQTT, JSON Parser, and AWS IoT Device Shadow libraries for optimized memory usage and modularity. These libraries are included in the SDK via Git submoduling. These libraries have 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. These libraries have also undergone both static code analysis from Coverity static analysis, and validation of memory safety and data structure invariance through the CBMC automated reasoning tool.

If you are upgrading from v3.x API of the C-SDK to the 202009.00 release, please refer to Migration guide from v3.1.2 to 202009.00 and newer releases. If you are using the C-SDK v4_beta_deprecated branch, note that we will continue to maintain this branch for critical bug fixes and security patches but will not add new features to it. See the C-SDK v4_beta_deprecated branch README for additional details.

v3.1.2

Details available here.

Porting Guide for 202009.00 and newer releases

All libraries depend on the ISO C90 standard library and additionally on the stdint.h library for fixed-width integers, including uint8_t, int8_t, uint16_t, uint32_t and int32_t, and constant macros like UINT16_MAX. If your platform does not support the stdint.h library, definitions of the mentioned fixed-width integer types will be required for porting any C-SDK library to your platform.

Porting coreMQTT

Guide for porting coreMQTT library to your platform is available here.

Porting coreHTTP

Guide for porting coreHTTP library is available here.

Porting AWS IoT Device Shadow

Guide for porting AWS IoT Device Shadow library is available here.

Porting AWS IoT Device Defender

Guide for porting AWS IoT Device Defender library is available here.

Porting AWS IoT Over-the-air Update

Guide for porting OTA library to your platform is available here.

Migration guide from v3.1.2 to 202009.00 and newer releases

MQTT Migration

Migration guide for MQTT library is available here.

Shadow Migration

Migration guide for Shadow library is available here.

Jobs Migration

Migration guide for Jobs library is available here.

Branches

main branch

The main branch hosts the continuous development of the AWS IoT Embedded C SDK (C-SDK) libraries. Please be aware that the development at the tip of the main branch is continuously in progress, and may have bugs. Consider using the tagged releases of the C-SDK for production ready software.

v4_beta_deprecated branch (formerly named v4_beta)

The v4_beta_deprecated branch contains a beta version of the C-SDK libraries, which is now deprecated. This branch was earlier named as v4_beta, and was renamed to v4_beta_deprecated. The libraries in this branch will not be released. However, critical bugs will be fixed and tested. No new features will be added to this branch.

Getting Started

Cloning

This repository uses Git Submodules to bring in the C-SDK libraries (eg, MQTT ) and third-party dependencies (eg, mbedtls for POSIX platform transport layer). Note: If you download the ZIP file provided by GitHub UI, you will not get the contents of the submodules (The ZIP file is also not a valid git repository). If you download from the 202012.00 Release Page page, you will get the entire repository (including the submodules) in the ZIP file, aws-iot-device-sdk-embedded-c-202012.00.zip. To clone the latest commit to main branch using HTTPS:

git clone --recurse-submodules https://github.com/aws/aws-iot-device-sdk-embedded-C.git

Using SSH:

git clone --recurse-submodules git@github.com:aws/aws-iot-device-sdk-embedded-C.git

If you have downloaded the repo without using the --recurse-submodules argument, you need to run:

git submodule update --init --recursive

When building with CMake, submodules are also recursively cloned automatically. However, -DBUILD_CLONE_SUBMODULES=0 can be passed as a CMake flag to disable this functionality. This is useful when you'd like to build CMake while using a different commit from a submodule.

Configuring Demos

The libraries in this SDK are not dependent on any operating system. However, the demos for the libraries in this SDK are built and tested on a Linux platform. The demos build with CMake, a cross-platform build tool.

Prerequisites

CMake 3.2.0 or any newer version for utilizing the build system of the repository.
C90 compiler such as gcc
- Due to the use of mbedtls in corePKCS11, a C99 compiler is required if building the PKCS11 demos or the CMake install target.
Although not a part of the ISO C90 standard, stdint.h is required for fixed-width integer types that include uint8_t, int8_t, uint16_t, uint32_t and int32_t, and constant macros like UINT16_MAX, while stdbool.h is required for boolean parameters in coreMQTT. For compilers that do not provide these header files, coreMQTT provides the files stdint.readme and stdbool.readme, which can be renamed to stdint.h and stdbool.h, respectively, to provide the required type definitions.
A supported operating system. The ports provided with this repo are expected to work with all recent versions of the following operating systems, although we cannot guarantee the behavior on all systems.
- Linux system with POSIX sockets, threads, RT, and timer APIs. (We have tested on Ubuntu 18.04).

Build Dependencies

The follow table shows libraries that need to be installed in your system to run certain demos. If a dependency is not installed and cannot be built from source, demos that require that dependency will be excluded from the default all target.

Dependency	Version	Usage
OpenSSL	1.1.0 or later	All TLS demos and tests with the exception of PKCS11
Mosquitto Client	1.4.10 or later	AWS IoT Jobs Mosquitto demo

AWS IoT Account Setup

You need to setup an AWS account and access the AWS IoT console for running the AWS IoT Device Shadow library, AWS IoT Device Defender library, AWS IoT Jobs library, AWS IoT OTA library and coreHTTP S3 download demos. Also, the AWS account can be used for running the MQTT mutual auth demo against AWS IoT broker. Note that running the AWS IoT Device Defender, AWS IoT Jobs and AWS IoT Device Shadow library demos require the setup of a Thing resource for the device running the demo. Follow the links to:

Setup an AWS account.
Sign-in to the AWS IoT Console after setting up the AWS account.
Create a Thing resource.

The MQTT Mutual Authentication and AWS IoT Shadow demos include example AWS IoT policy documents to run each respective demo with AWS IoT. You may use the MQTT Mutual auth and Shadow example policies by replacing [AWS_REGION] and [AWS_ACCOUNT_ID] with the strings of your region and account identifier. While the IoT Thing name and MQTT client identifier do not need to match for the demos to run, the example policies have the Thing name and client identifier identical as per AWS IoT best practices.

It can be very helpful to also have the AWS Command Line Interface tooling installed.

Configuring mutual authentication demos of MQTT and HTTP

You can pass the following configuration settings as command line options in order to run the mutual auth demos. Make sure to run the following command in the root directory of the C-SDK:

## optionally find your-aws-iot-endpoint from the command line
aws iot describe-endpoint --endpoint-type iot:Data-ATS
cmake -S . -Bbuild
-DAWS_IOT_ENDPOINT="<your-aws-iot-endpoint>" -DCLIENT_CERT_PATH="<your-client-certificate-path>" -DCLIENT_PRIVATE_KEY_PATH="<your-client-private-key-path>"

In order to set these configurations manually, edit demo_config.h in demos/mqtt/mqtt_demo_mutual_auth/ and demos/http/http_demo_mutual_auth/ to #define the following:

Set AWS_IOT_ENDPOINT to your custom endpoint. This is found on the Settings page of the AWS IoT Console and has a format of ABCDEFG1234567.iot.<aws-region>.amazonaws.com where <aws-region> can be an AWS region like us-east-2.
- Optionally, it can also be found with the AWS CLI command aws iot describe-endpoint --endpoint-type iot:Data-ATS.
Set CLIENT_CERT_PATH to the path of the client certificate downloaded when setting up the device certificate in AWS IoT Account Setup.
Set CLIENT_PRIVATE_KEY_PATH to the path of the private key downloaded when setting up the device certificate in AWS IoT Account Setup.

It is possible to configure ROOT_CA_CERT_PATH to any PEM-encoded Root CA Certificate. However, this is optional because CMake will download and set it to AmazonRootCA1.pem when unspecified.

Configuring AWS IoT Device Defender and AWS IoT Device Shadow demos

To build the AWS IoT Device Defender and AWS IoT Device Shadow demos, you can pass the following configuration settings as command line options. Make sure to run the following command in the root directory of the C-SDK:

cmake -S . -Bbuild -DAWS_IOT_ENDPOINT="<your-aws-iot-endpoint>" -DROOT_CA_CERT_PATH="<your-path-to-amazon-root-ca>" -DCLIENT_CERT_PATH="<your-client-certificate-path>" -DCLIENT_PRIVATE_KEY_PATH="<your-client-private-key-path>" -DTHING_NAME="<your-registered-thing-name>"

An Amazon Root CA certificate can be downloaded from here.

In order to set these configurations manually, edit demo_config.h in the demo folder to #define the following:

Set AWS_IOT_ENDPOINT to your custom endpoint. This is found on the Settings page of the AWS IoT Console and has a format of ABCDEFG1234567.iot.us-east-2.amazonaws.com.
Set ROOT_CA_CERT_PATH to the path of the root CA certificate downloaded when setting up the device certificate in AWS IoT Account Setup.
Set CLIENT_CERT_PATH to the path of the client certificate downloaded when setting up the device certificate in AWS IoT Account Setup.
Set CLIENT_PRIVATE_KEY_PATH to the path of the private key downloaded when setting up the device certificate in AWS IoT Account Setup.
Set THING_NAME to the name of the Thing created in AWS IoT Account Setup.

Configuring the AWS IoT Fleet Provisioning demo

To build the AWS IoT Fleet Provisioning Demo, you can pass the following configuration settings as command line options. Make sure to run the following command in the root directory of the C-SDK:

cmake -S . -Bbuild -DAWS_IOT_ENDPOINT="<your-aws-iot-endpoint>" -DROOT_CA_CERT_PATH="<your-path-to-amazon-root-ca>" -DCLAIM_CERT_PATH="<your-claim-certificate-path>" -DCLAIM_PRIVATE_KEY_PATH="<your-claim-private-key-path>" -DPROVISIONING_TEMPLATE_NAME="<your-template-name>" -DDEVICE_SERIAL_NUMBER="<your-serial-number>"

An Amazon Root CA certificate can be downloaded from here.

To create a provisioning template and claim credentials, sign into your AWS account and visit here. Make sure to enable the "Use the AWS IoT registry to manage your device fleet" option. Once you have created the template and credentials, modify the claim certificate's policy to match the sample policy.

In order to set these configurations manually, edit demo_config.h in the demo folder to #define the following:

Set AWS_IOT_ENDPOINT to your custom endpoint. This is found on the Settings page of the AWS IoT Console and has a format of ABCDEFG1234567.iot.us-east-2.amazonaws.com.
Set ROOT_CA_CERT_PATH to the path of the root CA certificate downloaded when setting up the device certificate in AWS IoT Account Setup.
Set CLAIM_CERT_PATH to the path of the claim certificate downloaded when setting up the template and claim credentials.
Set CLAIM_PRIVATE_KEY_PATH to the path of the private key downloaded when setting up the template and claim credentials.
Set PROVISIONING_TEMPLATE_NAME to the name of the provisioning template created.
Set DEVICE_SERIAL_NUMBER to an arbitrary string representing a device identifier.

Configuring the S3 demos

You can pass the following configuration settings as command line options in order to run the S3 demos. Make sure to run the following command in the root directory of the C-SDK:

cmake -S . -Bbuild -DS3_PRESIGNED_GET_URL="s3-get-url" -DS3_PRESIGNED_PUT_URL="s3-put-url"

S3_PRESIGNED_PUT_URL is only needed for the S3 upload demo.

In order to set these configurations manually, edit demo_config.h in demos/http/http_demo_s3_download_multithreaded, and demos/http/http_demo_s3_upload to #define the following:

Set S3_PRESIGNED_GET_URL to a S3 presigned URL with GET access.
Set S3_PRESIGNED_PUT_URL to a S3 presigned URL with PUT access.

You can generate the presigned urls using demos/http/common/src/presigned_urls_gen.py. More info can be found here.

Configure S3 Download HTTP Demo using SigV4 Library:

Refer this demos/http/http_demo_s3_download/README.md to follow the steps needed to configure and run the S3 Download HTTP Demo using SigV4 Library that generates the authorization HTTP header needed to authenticate the HTTP requests send to S3.

Setup for AWS IoT Jobs demo

The demo requires the Linux platform to contain curl and libmosquitto. On a Debian platform, these dependencies can be installed with:

    apt install curl libmosquitto-dev

If the platform does not contain the libmosquitto library, the demo will build the library from source.

libmosquitto 1.4.10 or any later version of the first major release is required to run this demo.

A job that specifies the URL to download for the demo needs to be created on the AWS account for the Thing resource that will be used by the demo.
The job can be created directly from the AWS IoT console or using the aws cli tool.

The following creates a job that specifies a Linux Kernel link for downloading.

 aws iot create-job \
        --job-id 'job_1' \
        --targets arn:aws:iot:us-west-2:<account-id>:thing/<thing-name> \
        --document '{"url":"https://cdn.kernel.org/pub/linux/kernel/v5.x/linux-5.8.5.tar.xz"}'

Prerequisites for the AWS Over-The-Air Update (OTA) demos

To perform a successful OTA update, you need to complete the prerequisites mentioned here.
A code signing certificate is required to authenticate the update. A code signing certificate based on the SHA-256 ECDSA algorithm will work with the current demos. An example of how to generate this kind of certificate can be found here.

Scheduling an OTA Update Job

After you build and run the initial executable you will have to create another executable and schedule an OTA update job with this image.

Increase the version of the application by setting macro APP_VERSION_BUILD in demos/ota/ota_demo_core_[mqtt/http]/demo_config.h to a different version than what is running.
Rebuild the application using the build steps below into a different directory, say build-dir-2.
Rename the demo executable to reflect the change, e.g. mv ota_demo_core_mqtt ota_demo_core_mqtt2
Create an OTA job:
1. Go to the AWS IoT Core console.
2. Manage → Jobs → Create → Create a FreeRTOS OTA update job → Select the corresponding name for your device from the thing list.
3. Sign a new firmware → Create a new profile → Select any SHA-ECDSA signing platform → Upload the code signing certificate(from prerequisites) and provide its path on the device.
4. Select the image → Select the bucket you created during the prerequisite steps → Upload the binary build-dir-2/bin/ota_demo2.
5. The path on device should be the absolute path to place the executable and the binary name: e.g. /home/ubuntu/aws-iot-device-sdk-embedded-C-staging/build-dir/bin/ota_demo_core_mqtt2.
6. Select the IAM role created during the prerequisite steps.
7. Create the Job.
Run the initial executable again with the following command: sudo ./ota_demo_core_mqtt or sudo ./ota_demo_core_http.
After the initial executable has finished running, go to the directory where the downloaded firmware image resides which is the path name used when creating an OTA job.
Change the permissions of the downloaded firmware to make it executable, as it may be downloaded with read (user default) permissions only: chmod 775 ota_demo_core_mqtt2
Run the downloaded firmware image with the following command: sudo ./ota_demo_core_mqtt2

Building and Running Demos

Before building the demos, ensure you have installed the prerequisite software. On Ubuntu 18.04 and 20.04, gcc, cmake, and OpenSSL can be installed with:

sudo apt install build-essential cmake libssl-dev

Build a single demo

Go to the root directory of the C-SDK.
Run cmake to generate the Makefiles: cmake -S . -Bbuild && cd build
Choose a demo from the list below or alternatively, run make help | grep demo:

defender_demo
http_demo_basic_tls
http_demo_mutual_auth
http_demo_plaintext
http_demo_s3_download
http_demo_s3_download_multithreaded
http_demo_s3_upload
jobs_demo_mosquitto
mqtt_demo_basic_tls
mqtt_demo_mutual_auth
mqtt_demo_plaintext
mqtt_demo_serializer
mqtt_demo_subscription_manager
ota_demo_core_http
ota_demo_core_mqtt
pkcs11_demo_management_and_rng
pkcs11_demo_mechanisms_and_digests
pkcs11_demo_objects
pkcs11_demo_sign_and_verify
shadow_demo_main

Replace demo_name with your desired demo then build it: make demo_name
Go to the build/bin directory and run any demo executables from there.

Build all configured demos

Go to the root directory of the C-SDK.
Run cmake to generate the Makefiles: cmake -S . -Bbuild && cd build
Run this command to build all configured demos: make
Go to the build/bin directory and run any demo executables from there.

Running corePKCS11 demos

The corePKCS11 demos do not require any AWS IoT resources setup, and are standalone. The demos build upon each other to introduce concepts in PKCS #11 sequentially. Below is the recommended order.

pkcs11_demo_management_and_rng
pkcs11_demo_mechanisms_and_digests
pkcs11_demo_objects
pkcs11_demo_sign_and_verify
1. Please note that this demo requires the private and public key generated from pkcs11_demo_objects to be in the directory the demo is executed from.

Alternative option of Docker containers for running demos locally

Install Docker:

curl -fsSL https://get.docker.com -o get-docker.sh

sh get-docker.sh

Installing Mosquitto to run MQTT demos locally

The following instructions have been tested on an Ubuntu 18.04 environment with Docker and OpenSSL installed.

Download the official Docker image for Mosquitto 1.6.14. This version is deliberately chosen so that the Docker container can load certificates from the host system. Any version after 1.6.14 will drop privileges as soon as the configuration file has been read (before TLS certificates are loaded).

docker pull eclipse-mosquitto:1.6.14

If a Mosquitto broker with TLS communication needs to be run, ignore this step and proceed to the next step. A Mosquitto broker with plain text communication can be run by executing the command below.

docker run -it -p 1883:1883 --name mosquitto-plain-text eclipse-mosquitto:1.6.14

Set BROKER_ENDPOINT defined in demos/mqtt/mqtt_demo_plaintext/demo_config.h to localhost.

Ignore the remaining steps unless a Mosquitto broker with TLS communication also needs to be run.

For TLS communication with Mosquitto broker, server and CA credentials need to be created. Use OpenSSL commands to generate the credentials for the Mosquitto server.

# Generate CA key and certificate. Provide the Subject field information as appropriate for CA certificate.
openssl req -x509 -nodes -sha256 -days 365 -newkey rsa:2048 -keyout ca.key -out ca.crt

# Generate server key and certificate.# Provide the Subject field information as appropriate for Server certificate. Make sure the Common Name (CN) field is different from the root CA certificate.
openssl req -nodes -sha256 -new -keyout server.key -out server.csr # Sign with the CA cert.
openssl x509 -req -sha256 -in server.csr -CA ca.crt -CAkey ca.key -CAcreateserial -out server.crt -days 365

Note: Make sure to use different Common Name (CN) detail between the CA and server certificates; otherwise, SSL handshake fails with exactly same Common Name (CN) detail in both the certificates.

port 8883

cafile /mosquitto/config/ca.crt
certfile /mosquitto/config/server.crt
keyfile /mosquitto/config/server.key

# Use this option for TLS mutual authentication (where client will provide CA signed certificate)
#require_certificate true
tls_version tlsv1.2
#use_identity_as_username true

Create a mosquitto.conf file to use port 8883 (for TLS communication) and providing path to the generated credentials.

Run the docker container from the local directory containing the generated credential and mosquitto.conf files.

docker run -it -p 8883:8883 -v $(pwd):/mosquitto/config/ --name mosquitto-basic-tls eclipse-mosquitto:1.6.14

Update demos/mqtt/mqtt_demo_basic_tls/demo_config.h to the following:
Set BROKER_ENDPOINT to localhost.
Set ROOT_CA_CERT_PATH to the absolute path of the CA certificate created in step 4. for the local Mosquitto server.

Installing httpbin to run HTTP demos locally

Run httpbin through port 80:

docker pull kennethreitz/httpbin
docker run -p 80:80 kennethreitz/httpbin

SERVER_HOST defined in demos/http/http_demo_plaintext/demo_config.h can now be set to localhost.

To run http_demo_basic_tls, download ngrok in order to create an HTTPS tunnel to the httpbin server currently hosted on port 80:

./ngrok http 80 # May have to use ./ngrok.exe depending on OS or filename of the executable

ngrok will provide an https link that can be substituted in demos/http/http_demo_basic_tls/demo_config.h and has a format of https://ABCDEFG12345.ngrok.io.

Set SERVER_HOST in demos/http/http_demo_basic_tls/demo_config.h to the https link provided by ngrok, without https:// preceding it.

You must also download the Root CA certificate provided by the ngrok https link and set ROOT_CA_CERT_PATH in demos/http/http_demo_basic_tls/demo_config.h to the file path of the downloaded certificate.

Installation

The C-SDK libraries and platform abstractions can be installed to a file system through CMake. To do so, run the following command in the root directory of the C-SDK. Note that installation is not required to run any of the demos.

cmake -S . -Bbuild -DBUILD_DEMOS=0 -DBUILD_TESTS=0
cd build
sudo make install

Note that because make install will automatically build the all target, it may be useful to disable building demos and tests with -DBUILD_DEMOS=0 -DBUILD_TESTS=0 unless they have already been configured. Super-user permissions may be needed if installing to a system include or system library path.

To install only a subset of all libraries, pass -DINSTALL_LIBS to install only the libraries you need. By default, all libraries will be installed, but you may exclude any library that you don't need from this list:

-DINSTALL_LIBS="DEFENDER;SHADOW;JOBS;OTA;OTA_HTTP;OTA_MQTT;BACKOFF_ALGORITHM;HTTP;JSON;MQTT;PKCS"

By default, the install path will be in the project directory of the SDK. You can also set -DINSTALL_TO_SYSTEM=1 to install to the system path for headers and libraries in your OS (e.g. /usr/local/include & /usr/local/lib for Linux).

Upon entering make install, the location of each library will be specified first followed by the location of all installed headers:

-- Installing: /usr/local/lib/libaws_iot_defender.so
-- Installing: /usr/local/lib/libaws_iot_shadow.so
...
-- Installing: /usr/local/include/aws/defender.h
-- Installing: /usr/local/include/aws/defender_config_defaults.h
-- Installing: /usr/local/include/aws/shadow.h
-- Installing: /usr/local/include/aws/shadow_config_defaults.h

You may also set an installation path of your choice by passing the following flags through CMake. Make sure to run the following command in the root directory of the C-SDK:

cmake -S . -Bbuild -DBUILD_DEMOS=0 -DBUILD_TESTS=0 \
-DCSDK_HEADER_INSTALL_PATH="/header/path" -DCSDK_LIB_INSTALL_PATH="/lib/path"
cd build
sudo make install

POSIX platform abstractions are used together with the C-SDK libraries in the demos. By default, these abstractions are also installed but can be excluded by passing the flag: -DINSTALL_PLATFORM_ABSTRACTIONS=0.

Lastly, a custom config path for any specific library can also be specified through the following CMake flags, allowing libraries to be compiled with a config of your choice:

-DDEFENDER_CUSTOM_CONFIG_DIR="defender-config-directory"
-DSHADOW_CUSTOM_CONFIG_DIR="shadow-config-directory"
-DJOBS_CUSTOM_CONFIG_DIR="jobs-config-directory"
-DOTA_CUSTOM_CONFIG_DIR="ota-config-directory"
-DHTTP_CUSTOM_CONFIG_DIR="http-config-directory"
-DJSON_CUSTOM_CONFIG_DIR="json-config-directory"
-DMQTT_CUSTOM_CONFIG_DIR="mqtt-config-directory"
-DPKCS_CUSTOM_CONFIG_DIR="pkcs-config-directory"

Note that the file name of the header should not be included in the directory.

Generating Documentation

Note: For pre-generated documentation, please visit Releases and Documentation section.

The Doxygen references were created using Doxygen version 1.9.2. To generate the Doxygen pages, use the provided Python script at tools/doxygen/generate_docs.py. Please ensure that each of the library submodules under libraries/standard/ and libraries/aws/ are cloned before using this script.

cd <CSDK_ROOT>
git submodule update --init --recursive --checkout
python3 tools/doxygen/generate_docs.py

The generated documentation landing page is located at docs/doxygen/output/html/index.html.

Author: aws
Source code: https://github.com/aws/aws-iot-device-sdk-embedded-C
License: MIT license

#aws

Android Interview Questions – Get ready for your next interview

Android – one of the hottest technologies, which is having a bright future. Get ready to crack your next interview with the following android interview questions. These interview questions start with basic and cover deep concepts along with advanced topics.

Android Interview Questions for Freshers

1. What is Android?

Android is an open-source mobile operating system that is based on the modified versions of Linux kernel. Though it was mainly designed for smartphones, now it is being used for Tablets, Televisions, Smartwatches, and other Android wearables.

2. Who is the inventor of Android Technology?

The inventors of Android Technology are- Andry Rubin, Nick Sears, and Rich Miner.

3. What is the latest version of Android?

The latest version of Android is Android 10.0, known as Android Q. The upcoming major Android release is Android 11, which is the 18th version of Android. [Note: Keep checking the versions, it is as of June 2020.]

4. How many Android versions can you recall right now?

Till now, there are 17 versions of Android, which have their names in alphabetical order. The 18th version of Android is also going to come later this year. The versions of Android are here:

Android 1.0 – Its release is 23 September 2008.
Android 1.1 – Its release date is 9 February 2009.
Android 1.5 – Its name is Cupcake, Released on 27 April 2009.
Android 1.6 – Its name is Donut, Released on 15 September 2009.
Android 2.0 – Its name is Eclair, Released on 26 October 2009
Android 2.2 – Its name is Froyo, Released on 20 May 2010.
Android 2.3 – Its name is Gingerbread, Released on 06 December 2010.
Android 3.0 – Its name is Honeycomb, Released on 22 February 2011.
Android 4.0 – Its name is Ice Cream Sandwich, Released on 18 October 2011.
Android 4.1 – Its name is Jelly Bean, Released on 9 July 2012.
Android 4.4 – Its name is KitKat, Released on 31 October 2013.
Android 5.0 – Its name is Lollipop, Released on 12 November 2014.
Android 6.0 – Its name is Marshmallow, Released on 5 October 2015.
Android 7.0 – Its name is Nougat, Released on 22 August 2016.
Android 8.0 – Its name is Oreo, Released on 21 August 2017.
Android 9.0 – Its name is Pie, Released on 6 August 2018.
Android 10.0 – Its name is Android Q, Released on 3 September 2019.
Android 11.0 – As of now, it is Android 11.

5. Explain the Android Architecture with its components.

This is a popular android developer interview question

Android Architecture consists of 5 components that are-

a. Linux Kernel: It is the foundation of the Android Architecture that resides at the lowest level. It provides the level of abstraction for hardware devices and upper layer components. Linux Kernel also provides various important hardware drivers that act as software interfaces for hardwares like camera, bluetooth, etc.

b. Native Libraries: These are the libraries for Android that are written in C/C++. These libraries are useful to build many core services like ART and HAL. It provides support for core features.

c. Android Runtime: It is an Android Runtime Environment. Android Operating System uses it during the execution of the app. It performs the translation of the application bytecode into the native instructions. The runtime environment of the device then executes these native instructions.

d. Application Framework: Application Framework provides many java classes and interfaces for app development. And it also provides various high-level services. This complete Application framework makes use of Java.

e. Applications: This is the topmost layer of Android Architecture. It provides applications for the end-user, so they can use the android device and compute the tasks.

6. What are the services that the Application framework provides?

The Android application framework has the following key services-

a. Activity Manager: It uses testing and debugging methods.

b. Content provider: It provides the data from application to other layers.

c. Resource Manager: This provides users access to resources.

d. Notification Manager: This gives notification to the users regarding actions taking place in the background.

e. View System: It is the base class for widgets, and it is also responsible for event handling.

7. What are the important features of Linux Kernel?

The important features of the Linux Kernel are as follows:

a. Power Management: Linux Kernel does power management to enhance and improve the battery life of the device.

b. Memory Management: It is useful for the maximum utilization of the available memory of the device.

c. Device Management: It includes managing all the hardware device drivers. It maximizes the utilization of the available resources.

d. Security: It ensures that no application has any such permission that it affects any other application in order to maintain security.

e. Multi-tasking: Multi-tasking provides the users the ease of doing multiple tasks at the same time.

8. What are the building blocks of an Android Application?

This is a popular android interview question for freshers.

The main components of any Android application are- Activity, Services, Content Provider, and Broadcast Receiver. You can understand them as follows:

a. Activity- It is a class that acts as the entry point representing a single screen to the user. It is like a window to show the user interface.

b. Services- Services are the longest-running component that runs in the background.

c. Content Provider- The content provider is an essential component that allows apps to share data between themselves.

d. Broadcast receivers- Broadcast receiver is another most crucial application component. It helps the apps to receive and respond to broadcast messages from the system or some other application.

9. What are the important components of Android Application?

The Components of Android application are listed below:

Widgets
Intents
Views
Notification
Fragments
Layout XML files
Resources

10. What are the widgets?

Widgets are the variations of Broadcast receivers. They are an important part of home screen customization. They often display some data and also allow users to perform actions on them. Mostly they display the app icon on the screen.

11. Can you name some types of widgets?

Mentioned below are the types of widgets-

a. Informative Widgets: These widgets show some important information. Like, the clock widget or a weather widget.

b. Collective Widgets: They are the collection of some types of elements. For example, a music widget that lets us change, skip, or forward the song.

c. Control Widgets: These widgets help us control the actions within the application through it. Like an email widget that helps check the recent mails.

d. Hybrid Widgets: Hybrid widgets are those that consist of at least two or more types of widgets.

12. What are Intents?

Intents are an important part of Android Applications. They enable communication between components of the same application as well as separate applications. The Intent signals the Android system about a certain event that has occurred.

13. Explain the types of intents briefly?

Intent is of three types that are-

a. Implicit Intents: Implicit intents are those in which there is no description of the component name but only the action.

b. Explicit Intents: In explicit intents, the target component is present by declaring the name of the component.

c. Pending Intents: These are those intents that act as a shield over the Intent objects. It covers the intent objects and grants permission to the external app components to access them.

14. What is a View?

A view is an important building block that helps in designing the user interface of the application. It can be a rectangular box or a circular shape, for example, Text View, Edit Text, Buttons, etc. Views occupy a certain area of the screen, and it is also responsible for event handling. A view is the superclass of all the graphical user interface components.

15. What do you understand by View Group?

It is the subclass of the ViewClass. It gives an invisible container to hold layouts or views. You can understand view groups as special views that are capable of holding other views, that are Child View.

16. What do you understand about Shared Preferences?

It is a simple mechanism for data storage in Android. In this, there is no need to create files, and using APIs, it stores the data in XML files. It stores the data in the pair of key-values. SharedPreferences class lets the user save the values and retrieve them when required. Using SharedPreferences we can save primitive data like- boolean, float, integer, string and long.

17. What is a Notification?

A notification is just like a message that shows up outside the Application UI to provide reminders to the users. They remind the user about a message received, or some other timely information from the app.

18. Give names of Notification types.

There are three types of notifications namely-

a. Toast Notification- This notification is the one that fades away sometime after it pops up.

b. Status Notification- This notification stays till the user takes some action on it.

c. Dialog Notification- This notification is the result of an Active Activity.

19. What are fragments?

A fragment is a part of the complete user interface. These are present in Activity, and an activity can have one or more fragments at the same time. We can reuse a fragment in multiple activities as well.

20. What are the types of fragments?

There are three types of fragments that are: Single Fragment, List Fragment, Fragment Transactions.

Single Transactions can only show a single view for the user.
List Fragments have a special list view feature that provides a list from which the user can select one.
Fragment Transactions are helpful for the transition between one fragment to the other.

Frequently asked Android Interview Questions and Answers

21. What are Layout XML files?

Layout XML files contain the structure for the user interface of the application. The XML file also contains various different layouts and views, and they also specify various GUI components that are there in Activity or fragments.

22. What are Resources in Android Application?

The resources in Android Apps defines images, texts, strings, colors, etc. Everything in resources directory is referenced in the source code of the app so that we can use them.

23. Can you develop Android Apps with languages other than Java? If so, name some.

Yes, there are many languages that we can work with, for the development of Android Applications. To name some, I would say Java, Python, C, C++, Kotlin, C#, Corona/LUA.

24. What are the states of the Activity Lifecycle?

Activity lifecycle has the following four stages-

a. Running State: As soon as the activity starts, it is the first state.

b. Paused State: When some other activity starts without closing the previous one, the running activity turns into the Paused state.

c. Resume State: When the activity opens again after being in pause state, it comes into the Resume State.

d. Stopped State: When the user closes the application or stops using it, the activity goes to the Stopped state.

25. What are some methods of Activity?

The methods of Activity are as follows:

onCreate()
onStart()
onPause()
onRestart()
onResume()
onStop()
onDestroy()

26. How can you launch an activity in Android?

We launch an activity using Intents. For this we need to use intent as follows:

ntent intent_name= new Intent(this, Activity_name.class);
startActivity(intent_name);

27. What is the service lifecycle?

There are two states of a service that are-

a. Started State: This is when the service starts its execution. A Services come in start state only through the startService() method.

b. Bounded State: A service is in the bounded state when it calls the method bindService().

28. What are some methods of Services?

The methods of service are as follows-

onStartCommand()
onBind()
onCreate()
onUnbind()
onDestroy()
onRebind()

29. What are the types of Broadcast?

Broadcasts are of two types that are-

a. Ordered Broadcast: Ordered broadcasts are Synchronous and work in a proper order. It decides the order by using the priority assigned to the broadcasts.

b. Normal Broadcast: These are asynchronous and unordered. They are more efficient as they run unorderly and all at once. But, they lack full utilization of the results.

30. What are useful impotent folders in Android?

The impotent folders in an Android application are-

build.xml- It is responsible for the build of Android applications.
bin/ – The bin folder works as a staging area to wrap the files packages into the APK.
src/ – The src is a folder where all the source files of the project are present.
res/ – The res is the resource folder that stores values of the resources that are used in the application. These resources can be colors, styles, strings, dimensions, etc.
assets/ – It provides a facility to include files like text, XML, fonts, music, and video in the Android application.

31. What are the important files for Android Application when working on Android Studio?

This is an important android studio interview question

There are following three files that we need to work on for an application to work-

a. The AndroidManifest.xml file: It has all the information about the application.

b. The MainActivity.java file: It is the app file that actually gets converted to the dalvik executable and runs the application. It is written in java.

c. The Activity_main.xml file: It is the layout file that is available in the res/layout directory. It is another mostly used file while developing the application.

32. Which database do you use for Android Application development?

The database that we use for Android Applications is SQLite. It is because SQLite is lightweight and specially developed for Android Apps. SQLite works the same way as SQL using the same commands.

33. Tell us some features of Android OS.

The best features of Android include-

Multi-tasking
Support for a great range of languages
Support for split-screen
High connectivity with 5G support
Motion Control

34. Why did you learn Android development?

Learning Android Studio is a good idea because of the following-

It has a low application development cost.
It is an open-source platform.
It has multi-platform support as well as Multi-carrier support.
It is open for customizations.
Android is a largely used operating system throughout the world.

35. What are the different ways of storage supported in Android?

The various storage ways supported in Android are as follows:

Shared Preference
Internal Storage
External Storage
SQLite Databases
Network Connection

36. What are layouts?

Layout is nothing but arrangements of elements on the device screen. These elements can be images, tests, videos, anything. They basically define the structure of the Android user interface to make it user friendly.

37. How many layout types are there?

The type of layouts used in Android Apps are as follows:

Linear Layout
Relative Layout
Constraint Layout
Table Layout
Frame Layout
Absolute Layout
Scrollview layout

38. What is an APK?

An APK stands for Android Package that is a file format of Android Applications. Android OS uses this package for the distribution and installation of the Android Application.

39. What is an Android Manifest file?

The manifest file describes all the essential information about the project application for build tools, Android operating system, and google play. This file is a must for every Android project that we develop, and it is present in the root of the project source set.

#android tutorials #android basic interview questions #android basic questions #android developer interview questions #android interview question and answer #android interview questions #android interview questions for experienced #android interview questions for fresher

11 Tricky JavaScript Questions

AWS IoT Device SDK for Embedded C

Overview

License

Features

coreMQTT

coreHTTP

coreJSON

corePKCS11

AWS IoT Device Shadow

AWS IoT Jobs

AWS IoT Device Defender

AWS IoT Over-the-air Update

AWS IoT Fleet Provisioning

AWS SigV4

backoffAlgorithm

Sending metrics to AWS IoT

Versioning

Releases and Documentation

202108.00

202103.00

202012.01

202011.00

202009.00

v3.1.2

Porting Guide for 202009.00 and newer releases

Porting coreMQTT

Porting coreHTTP

Porting AWS IoT Device Shadow

Porting AWS IoT Device Defender

Porting AWS IoT Over-the-air Update

Migration guide from v3.1.2 to 202009.00 and newer releases

MQTT Migration

Shadow Migration

Jobs Migration

Branches

main branch

v4_beta_deprecated branch (formerly named v4_beta)

Getting Started

Cloning

Configuring Demos

Prerequisites

AWS IoT Account Setup

Configuring mutual authentication demos of MQTT and HTTP

Configuring AWS IoT Device Defender and AWS IoT Device Shadow demos

Configuring the AWS IoT Fleet Provisioning demo

Configuring the S3 demos

Configure S3 Download HTTP Demo using SigV4 Library:

Setup for AWS IoT Jobs demo

Prerequisites for the AWS Over-The-Air Update (OTA) demos

Scheduling an OTA Update Job

Building and Running Demos

Build a single demo

Build all configured demos

Running corePKCS11 demos

Alternative option of Docker containers for running demos locally

Installation

Generating Documentation

Android Interview Questions – Get ready for your next interview

Android Interview Questions for Freshers

Frequently asked Android Interview Questions and Answers

Who invented JavaScript?

What is JavaScript?

JavaScript Hello World Program

How to comment JavaScript code?