如何使用 AWS CLI 为 IoT 设备发送十六进制字符串？

Question

I'm trying to send a stream of data to an IoT device. The general data flow is:

• Send payload via AWS CLI or custom tool written by coworkers.
• Lambda function receives base64 encoded payload, converts to hex string, and forwards data to device.
• Device unescapes the data and then parses it to run a command.

The issue I'm running into is this: we would like to move away from using a very fragile custom tool since we're a small team and the devs who wrote it have moved on. The AWS CLI only accepts raw or base64 encodings for data, and my current input is a hex string like "C00020000000ff64". I am able to send data with the following commands in a powershell script:

$tmp="<SOME_HEX_STRING>"
$tmp -split '(.{2})' | %{ if ($_ -ne "") { $payload += [CHAR]([CONVERT]::toint16("$_",16)) }}
aws --region <SOME_AWS_REGION> iot-data publish --topic "<TOPIC_ID_HERE>" --cli-binary-format raw-in-base64-out --payload "$payload"

However, the base64 parsing by the lambda function seems to barf at this approach and I get mangled data on the IoT device. I do not currently have debug access to our server to check the logs, but the actual parsing is done in node as a simple Buffer.from(event.payload, 'base64') , which is then parsed into an object containing a hex string. My impression is that the encoding method I'm using for input with the CLI is likely wrong (I strongly suspect that [CHAR] cast, to be honest), but I don't know enough in this situation to be able to identify where the problem is in my code, and Python (the code base for AWS CLI) is not my strong suit, so looking at their repo has only led to dead ends, moreso since there are no examples for using aws iot-data publish .

So my question is this:

Does anyone have a reliable method of converting a hex string to base64 or raw binary for input with AWS CLI?

Answer 1

If the hex string is being passed to Python, I believe it is expecting a UTF8 Base64 Enconded string. Your current $payload is definitely not Base64.

This is how you can encode your payload:

$tmp = 'C00020000000ff64'

$payload = [convert]::ToBase64String(
    [System.Text.Encoding]::UTF8.GetBytes($tmp)
)

python3 ./decode.py $payload # => Decoded from Python: b'C00020000000ff64'

• decode.py

import base64, sys

print(
    'Decoded from Python: {0}'.format(base64.b64decode(sys.argv[1]))
)