11 Tips for Cracking your Next Coding Interview

This is a very vast topic as different companies have different ways to conduct a technical interview, I am going to share few tips to do well on traditional coding interviews, where you need to solve coding problems face-to-face, on whiteboards, or on a phone call. The important thing here is that a person is interviewing you.

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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

1. 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.

1. 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

1. To perform a successful OTA update, you need to complete the prerequisites mentioned here.
2. 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.

1. 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.
2. Rebuild the application using the build steps below into a different directory, say build-dir-2.
3. Rename the demo executable to reflect the change, e.g. mv ota_demo_core_mqtt ota_demo_core_mqtt2
4. 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.
5. Run the initial executable again with the following command: sudo ./ota_demo_core_mqtt or sudo ./ota_demo_core_http.
6. 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.
7. 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
8. 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.

1. pkcs11_demo_management_and_rng
2. pkcs11_demo_mechanisms_and_digests
3. pkcs11_demo_objects
4. 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 

How to Use Hotwire Rails

Introduction

We are back with another exciting and much-talked-about Rails tutorial on how to use Hotwire with the Rails application. This Hotwire Rails tutorial is an alternate method for building modern web applications that consume a pinch of JavaScript.

Rails 7 Hotwire is the default front-end framework shipped with Rails 7 after it was launched. It is used to represent HTML over the wire in the Rails application. Previously, we used to add a hotwire-rails gem in our gem file and then run rails hotwire: install. However, with the introduction of Rails 7, the gem got deprecated. Now, we use turbo-rails and stimulus rails directly, which work as Hotwire’s SPA-like page accelerator and Hotwire’s modest JavaScript framework.

What is Hotwire?

Hotwire is a package of different frameworks that help to build applications. It simplifies the developer’s work for writing web pages without the need to write JavaScript, and instead sending HTML code over the wire.

Introduction to The Hotwire Framework:

1. Turbo:

It uses simplified techniques to build web applications while decreasing the usage of JavaScript in the application. Turbo offers numerous handling methods for the HTML data sent over the wire and displaying the application’s data without actually loading the entire page. It helps to maintain the simplicity of web applications without destroying the single-page application experience by using the below techniques:

Turbo Frames: Turbo Frames help to load the different sections of our markup without any dependency as it divides the page into different contexts separately called frames and updates these frames individually.
Turbo Drive: Every link doesn’t have to make the entire page reload when clicked. Only the HTML contained within the tag will be displayed.
Turbo Streams: To add real-time features to the application, this technique is used. It helps to bring real-time data to the application using CRUD actions.

2. Stimulus

It represents the JavaScript framework, which is required when JS is a requirement in the application. The interaction with the HTML is possible with the help of a stimulus, as the controllers that help those interactions are written by a stimulus.

3. Strada

Not much information is available about Strada as it has not been officially released yet. However, it works with native applications, and by using HTML bridge attributes, interaction is made possible between web applications and native apps.

Simple diagrammatic representation of Hotwire Stack:

Prerequisites For Hotwire Rails Tutorial

As we are implementing the Ruby on Rails Hotwire tutorial, make sure about the following installations before you can get started.

• Ruby on Rails
• Hotwire gem
• PostgreSQL/SQLite (choose any one database)
• Turbo Rails
• Stimulus.js

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Create a new Rails Project

Find the following commands to create a rails application.

mkdir ~/projects/railshotwire
cd ~/projects/railshotwire
echo "source 'https://rubygems.org'" > Gemfile
echo "gem 'rails', '~> 7.0.0'" >> Gemfile
bundle install  
bundle exec rails new . --force -d=postgresql

Now create some files for the project, up till now no usage of Rails Hotwire can be seen.
Fire the following command in your terminal.

• For creating a default controller for the application

echo "class HomeController < ApplicationController" > app/controllers/home_controller.rb
echo "end" >> app/controllers/home_controller.rb

• For creating another controller for the application

echo "class OtherController < ApplicationController" > app/controllers/other_controller.rb
echo "end" >> app/controllers/home_controller.rb

• For creating routes for the application

echo "Rails.application.routes.draw do" > config/routes.rb
echo '  get "home/index"' >> config/routes.rb
echo '  get "other/index"' >> config/routes.rb
echo '  root to: "home#index"' >> config/routes.rb
echo 'end' >> config/routes.rb

• For creating a default view for the application

mkdir app/views/home
echo '<h1>This is Rails Hotwire homepage</h1>' > app/views/home/index.html.erb
echo '<div><%= link_to "Enter to other page", other_index_path %></div>' >> app/views/home/index.html.erb

• For creating another view for the application

mkdir app/views/other
echo '<h1>This is Another page</h1>' > app/views/other/index.html.erb
echo '<div><%= link_to "Enter to home page", root_path %></div>' >> app/views/other/index.html.erb

• For creating a database and schema.rb file for the application

bin/rails db:create
bin/rails db:migrate

• For checking the application run bin/rails s and open your browser, your running application will have the below view.

Additionally, you can clone the code and browse through the project. Here’s the source code of the repository: Rails 7 Hotwire application

Now, let’s see how Hotwire Rails can work its magic with various Turbo techniques.

Hotwire Rails: Turbo Drive

Go to your localhost:3000 on your web browser and right-click on the Inspect and open a Network tab of the DevTools of the browser.

Now click on go to another page link that appears on the home page to redirect from the home page to another page. In our Network tab, we can see that this action of navigation is achieved via XHR. It appears only the part inside HTML is reloaded, here neither the CSS is reloaded nor the JS is reloaded when the navigation action is performed.

By performing this action we can see that Turbo Drive helps to represent the HTML response without loading the full page and only follows redirect and reindeer HTML responses which helps to make the application faster to access.

Hotwire Rails: Turbo Frame

This technique helps to divide the current page into different sections called frames that can be updated separately independently when new data is added from the server.
Below we discuss the different use cases of Turbo frame like inline edition, sorting, searching, and filtering of data.

Let’s perform some practical actions to see the example of these use cases.

Make changes in the app/controllers/home_controller.rb file

#CODE

class HomeController < ApplicationController
   def turbo_frame_form
   end
   
   def turbo_frame submit
      extracted_anynumber = params[:any][:anynumber]
      render :turbo_frame_form, status: :ok, locals: {anynumber: extracted_anynumber,      comment: 'turbo_frame_submit ok' }
   end
end

Add app/views/home/turbo_frame_form.html.erb file to the application and add this content inside the file.

#CODE

<section>

    <%= turbo_frame_tag 'anyframe' do %>
            
      <div>
          <h2>Frame view</h2>
          <%= form_with scope: :any, url: turbo_frame_submit_path, local: true do |form| %>
              <%= form.label :anynumber, 'Type an integer (odd or even)', 'class' => 'my-0  d-inline'  %>
              <%= form.text_field :anynumber, type: 'number', 'required' => 'true', 'value' => "#{local_assigns[:anynumber] || 0}",  'aria-describedby' => 'anynumber' %>
              <%= form.submit 'Submit this number', 'id' => 'submit-number' %>
          <% end %>
      </div>
      <div>
        <h2>Data of the view</h2>
        <pre style="font-size: .7rem;"><%= JSON.pretty_generate(local_assigns) %></pre> 
      </div>
      
    <% end %>

</section>

Make some adjustments in routes.rb

#CODE

Rails.application.routes.draw do
  get 'home/index'
  get 'other/index'

  get '/home/turbo_frame_form' => 'home#turbo_frame_form', as: 'turbo_frame_form'
  post '/home/turbo_frame_submit' => 'home#turbo_frame_submit', as: 'turbo_frame_submit'


  root to: "home#index"
end

• Next step is to change homepage view in app/views/home/index.html.erb

#CODE

<h1>This is Rails Hotwire home page</h1>
<div><%= link_to "Enter to other page", other_index_path %></div>

<%= turbo_frame_tag 'anyframe' do %>        
  <div>
      <h2>Home view</h2>
      <%= form_with scope: :any, url: turbo_frame_submit_path, local: true do |form| %>
          <%= form.label :anynumber, 'Type an integer (odd or even)', 'class' => 'my-0  d-inline'  %>
          <%= form.text_field :anynumber, type: 'number', 'required' => 'true', 'value' => "#{local_assigns[:anynumber] || 0}",  'aria-describedby' => 'anynumber' %>
          <%= form.submit 'Submit this number', 'id' => 'submit-number' %>
      <% end %>
  <div>
<% end %>

After making all the changes, restart the rails server and refresh the browser, the default view will appear on the browser.

Now in the field enter any digit, after entering the digit click on submit button, and as the submit button is clicked we can see the Turbo Frame in action in the below screen, we can observe that the frame part changed, the first title and first link didn’t move.

Hotwire Rails: Turbo Streams

Turbo Streams deliver page updates over WebSocket, SSE or in response to form submissions by only using HTML and a series of CRUD-like operations, you are free to say that either

• Update the piece of HTML while responding to all the other actions like the post, put, patch, and delete except the GET action.
• Transmit a change to all users, without reloading the browser page.

This transmit can be represented by a simple example.

• Make changes in app/controllers/other_controller.rb file of rails application

#CODE

class OtherController < ApplicationController

  def post_something
    respond_to do |format|
      format.turbo_stream {  }
    end
  end

   end

Add the below line in routes.rb file of the application

#CODE

post '/other/post_something' => 'other#post_something', as: 'post_something'

Superb! Rails will now attempt to locate the app/views/other/post_something.turbo_stream.erb template at any moment the ‘/other/post_something’ endpoint is reached.

For this, we need to add app/views/other/post_something.turbo_stream.erb template in the rails application.

#CODE

<turbo-stream action="append" target="messages">
  <template>
    <div id="message_1">This changes the existing message!</div>
  </template>
</turbo-stream>

This states that the response will try to append the template of the turbo frame with ID “messages”.

Now change the index.html.erb file in app/views/other paths with the below content.

#CODE

<h1>This is Another page</h1>
<div><%= link_to "Enter to home page", root_path %></div>

<div style="margin-top: 3rem;">
  <%= form_with scope: :any, url: post_something_path do |form| %>
      <%= form.submit 'Post any message %>
  <% end %>
  <turbo-frame id="messages">
    <div>An empty message</div>
  </turbo-frame>
</div>

• After making all the changes, restart the rails server and refresh the browser, and go to the other page.

• Once the above screen appears, click on the Post any message button

This action shows that after submitting the response, the Turbo Streams help the developer to append the message, without reloading the page.

Another use case we can test is that rather than appending the message, the developer replaces the message. For that, we need to change the content of app/views/other/post_something.turbo_stream.erb template file and change the value of the action attribute from append to replace and check the changes in the browser.

#CODE

<turbo-stream action="replace" target="messages">
  <template>
    <div id="message_1">This changes the existing message!</div>
  </template>
</turbo-stream>

When we click on Post any message button, the message that appear below that button will get replaced with the message that is mentioned in the app/views/other/post_something.turbo_stream.erb template

Stimulus

There are some cases in an application where JS is needed, therefore to cover those scenarios we require Hotwire JS tool. Hotwire has a JS tool because in some scenarios Turbo-* tools are not sufficient. But as we know that Hotwire is used to reduce the usage of JS in an application, Stimulus considers HTML as the single source of truth. Consider the case where we have to give elements on a page some JavaScript attributes, such as data controller, data-action, and data target. For that, a stimulus controller that can access elements and receive events based on those characteristics will be created.

Make a change in app/views/other/index.html.erb template file in rails application

#CODE

<h1>This is Another page</h1>
<div><%= link_to "Enter to home page", root_path %></div>

<div style="margin-top: 2rem;">
  <%= form_with scope: :any, url: post_something_path do |form| %>
      <%= form.submit 'Post something' %>
  <% end %>
  <turbo-frame id="messages">
    <div>An empty message</div>
  </turbo-frame>
</div>

<div style="margin-top: 2rem;">
  <h2>Stimulus</h2>  
  <div data-controller="hello">
    <input data-hello-target="name" type="text">
    <button data-action="click->hello#greet">
      Greet
    </button>
    <span data-hello-target="output">
    </span>
  </div>
</div>

Make changes in the hello_controller.js in path app/JavaScript/controllers and add a stimulus controller in the file, which helps to bring the HTML into life.

#CODE

import { Controller } from "@hotwired/stimulus"

export default class extends Controller {
  static targets = [ "name", "output" ]

  greet() {
    this.outputTarget.textContent =
      `Hello, ${this.nameTarget.value}!`
  }
}

Go to your browser after making the changes in the code and click on Enter to other page link which will navigate to the localhost:3000/other/index page there you can see the changes implemented by the stimulus controller that is designed to augment your HTML with just enough behavior to make it more responsive.

With just a little bit of work, Turbo and Stimulus together offer a complete answer for applications that are quick and compelling.

Using Rails 7 Hotwire helps to load the pages at a faster speed and allows you to render templates on the server, where you have access to your whole domain model. It is a productive development experience in ROR, without compromising any of the speed or responsiveness associated with SPA.

Conclusion

We hope you were satisfied with our Rails Hotwire tutorial. Write to us at service@bacancy.com for any query that you want to resolve, or if you want us to share a tutorial on your query.

For more such solutions on RoR, check out our Ruby on Rails Tutorials. We will always strive to amaze you and cater to your needs.

Original article source at: https://www.bacancytechnology.com/

#rails #ruby 

How to Prepare for a Coding Interview in 8 Weeks

As of this writing, the market is tough. We’ve been hit hard with a deadly

pandemic that left thousands of people unemployed. It’s layoffs everywhere and the companies are being conservative when it comes to

hiring.

Companies are not willing to hire people with no experience or people who they’ve to train.

Your first job in tech is the toughest, you’re competing

with virtually every new college grad and anyone who completed a boot

camp. I know it can be hard to even land an interview, for someone to

give you a chance to talk and demonstrate you could be valuable

employee.

Now, the chance of you getting an interview totally depends on how your resume compares to the job description. The more relevant it is to the

skills required, the better your chances of getting an interview.

To build your resume, I’d recommend https://thetechresume.com. It’s a nice read to follow the principles when it comes to building a tech resume.

Over the past few months, I’ve been collecting resources like videos,

websites, and taking notes to prepare for coding interviews.

In that process, I made an 8 weeks study guide curated of important data

structure resources to prepare for tech interviews and honestly this

study guide was helpful to me to know what to study every day and in

following a routine for my job search.

Why 8 weeks?

If you’re serious about preparing for a tech interview then 8 weeks is the

minimum to be given to prepare thoroughly for a tech interview. I know

there are few who would cram up pools of content in a week or two. But, I

believe that is not a realistic or sensible approach.

Tech interviews can be intense and most companies expect you to solve problems or go through a data structure topic in detail.

Now, My study guide with resources will eat up the entire blog space. So,

Instead of straight-up dumping down the content all together, I racked

my brains on how to deliver the content in the most effective way

possible to ensure the habit of consistency and dedication stays intact

during the interview preparation process.

In this blog post, I would give you what to cover each week. If you’re

interested to know what resources to refer to when covering each topic then I’d recommend subscribing to the newsletter https://thedailycoding.com in which you’ll receive one email daily about the concept and the resources to practice.

If you believe you can find resources to relevant topics on your own then

here’s how you should plan to cover each topic every week.

#coding-interviews #software-development #job-interview #job-search #coding #latest-tech-stories #coding-interview-tips #coding-job-interview-advice

Static Code Analysis: What It Is? How to Use It?

Static code analysis refers to the technique of approximating the runtime behavior of a program. In other words, it is the process of predicting the output of a program without actually executing it.

Lately, however, the term “Static Code Analysis” is more commonly used to refer to one of the applications of this technique rather than the technique itself — program comprehension — understanding the program and detecting issues in it (anything from syntax errors to type mismatches, performance hogs likely bugs, security loopholes, etc.). This is the usage we’d be referring to throughout this post.

“The refinement of techniques for the prompt discovery of error serves as well as any other as a hallmark of what we mean by science.”

• J. Robert Oppenheimer

Outline

We cover a lot of ground in this post. The aim is to build an understanding of static code analysis and to equip you with the basic theory, and the right tools so that you can write analyzers on your own.

We start our journey with laying down the essential parts of the pipeline which a compiler follows to understand what a piece of code does. We learn where to tap points in this pipeline to plug in our analyzers and extract meaningful information. In the latter half, we get our feet wet, and write four such static analyzers, completely from scratch, in Python.

Note that although the ideas here are discussed in light of Python, static code analyzers across all programming languages are carved out along similar lines. We chose Python because of the availability of an easy to use ast module, and wide adoption of the language itself.

How does it all work?

Before a computer can finally “understand” and execute a piece of code, it goes through a series of complicated transformations:

As you can see in the diagram (go ahead, zoom it!), the static analyzers feed on the output of these stages. To be able to better understand the static analysis techniques, let’s look at each of these steps in some more detail:

Scanning

The first thing that a compiler does when trying to understand a piece of code is to break it down into smaller chunks, also known as tokens. Tokens are akin to what words are in a language.

A token might consist of either a single character, like (, or literals (like integers, strings, e.g., 7, Bob, etc.), or reserved keywords of that language (e.g, def in Python). Characters which do not contribute towards the semantics of a program, like trailing whitespace, comments, etc. are often discarded by the scanner.

Python provides the tokenize module in its standard library to let you play around with tokens:

Python

1

import io

2

import tokenize

3

4

code = b"color = input('Enter your favourite color: ')"

5

6

for token in tokenize.tokenize(io.BytesIO(code).readline):

7

    print(token)

Python

1

TokenInfo(type=62 (ENCODING),  string='utf-8')

2

TokenInfo(type=1  (NAME),      string='color')

3

TokenInfo(type=54 (OP),        string='=')

4

TokenInfo(type=1  (NAME),      string='input')

5

TokenInfo(type=54 (OP),        string='(')

6

TokenInfo(type=3  (STRING),    string="'Enter your favourite color: '")

7

TokenInfo(type=54 (OP),        string=')')

8

TokenInfo(type=4  (NEWLINE),   string='')

9

TokenInfo(type=0  (ENDMARKER), string='')

(Note that for the sake of readability, I’ve omitted a few columns from the result above — metadata like starting index, ending index, a copy of the line on which a token occurs, etc.)

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Ace Your Technical Interviews with These GitHub Repositories

Leverage these repositories to ace your next technical and coding interviews

Getting past the technical and coding interview is not always an easy task for most people.

Lucky for you, there are some amazing resources to help you go through easily and grab that position.

In this article, we will go through some of the best GitHub repositories to help you smash the coding interview.

These collections of repositories are essential in highlighting the different arears to focus on and different topics and questions to expect.

Front-end Developer Interview Questions

This repository is everything that entails frontend development.

Covered content includes:

• General Questions
• HTML Questions
• CSS Questions
• JS Questions
• Accessibility Questions (external link)
• Testing Questions
• Performance Questions
• Network Questions
• Coding Questions

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