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MQTT5 AWS Websocket PubSub

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Introduction

This sample uses the Message Broker for AWS IoT to send and receive messages through an MQTT connection using MQTT5 and a websocket as transport. Using websockets as transport requires the initial handshake request to be signed with the AWS Sigv4 signing algorithm. CredentialsProvider::CreateCredentialsProviderChainDefault is used to source credentials via the default credentials provider chain to sign the websocket handshake.

You can read more about MQTT5 for the CPP IoT Device SDK V2 in the MQTT5 user guide.

Requirements

The AWS IAM permission policy associated with the AWS credentials resolved by the default credentials provider chain must provide privileges for the sample to connect, subscribe, publish, and receive. Below is a sample policy will allow this sample to run as intended.

(see sample policy) 
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "iot:Publish",
        "iot:Receive"
      ],
      "Resource": [
        "arn:aws:iot:region:account:topic/test/topic"
      ]
    },
    {
      "Effect": "Allow",
      "Action": [
        "iot:Subscribe"
      ],
      "Resource": [
        "arn:aws:iot:region:account:topicfilter/test/topic"
      ]
    },
    {
      "Effect": "Allow",
      "Action": [
        "iot:Connect"
      ],
      "Resource": [
        "arn:aws:iot:region:account:client/mqtt5-sample-*"
      ]
    }
  ]
}

Replace with the following with the data from your AWS account:

  • <region>: The AWS IoT Core region where you created your AWS IoT Core thing you wish to use with this sample. For example us-east-1.
  • <account>: Your AWS IoT Core account ID. This is the set of numbers in the top right next to your AWS account name when using the AWS IoT Core website.

Note that in a real application, you may want to avoid the use of wildcards in your ClientID or use them selectively. Please follow best practices when working with AWS on production applications using the SDK. Also, for the purposes of this sample, please make sure your policy allows a client ID of mqtt5-sample-* to connect or use --client_id <client ID here> to send the client ID your policy supports.

How to build

To build the sample, change directory into the sample's folder and run the cmake commands. The sample executable will be built into the samples/mqtt/mqtt5_aws_websocket/build folder.

cd samples/mqtt/mqtt5_aws_websocket/
# If you followed the SDK build instruction, you would use the path to `sdk-workspace` folder for `CMAKE_PREFIX_PATH` here
cmake -B build -S . -DCMAKE_PREFIX_PATH="<absolute path sdk-workspace dir>" -DCMAKE_BUILD_TYPE="Debug" .
cmake --build build --config "Debug"

How to run

To run this sample, navigate to the build directory where the executable was created:

# From samples/mqtt/mqtt5_aws_websocket/, go to the build directory
cd build
./mqtt5_aws_websocket \
  --endpoint <AWS IoT endpoint> \
  --signing_region <Signing region for websocket connection>

If you would like to see what optional arguments are available, use the --help argument:

./mqtt5_aws_websocket --help

will result in the following output:

MQTT5 AWS Websocket Sample.

options:
  -h, --help         show this help message and exit

required arguments:
  --endpoint         IoT endpoint hostname 
  --signing_region   Signing region for websocket connection 

optional arguments:
  --client_id        Client ID (default: mqtt5-sample-<uuid>)
  --topic            Topic (default: test/topic)
  --message          Message payload (default: Hello from mqtt5 sample)
  --count            Messages to publish (0 = infinite) (default: 5)

The sample will not run without the required arguments and will notify you of missing arguments.

Additional Information

Additional help with the MQTT5 Client can be found in the MQTT5 Userguide. This guide will provide more details on MQTT5 operations, lifecycle events, connection methods, and other useful information.