No support for dt-subject on HTTP Transport

[ymoreiratiti]

Context

• OS and version used: Windows 11 with WSL2
• Node.js version: 16.15.1
• npm version: 8.12.2
• list of installed packages: {"azure-iot-device-http": "^1.14.0",}

Description of the issue

When using the HTTP transport layer, the message property "dt-subject" is transformed to "iothub-app-dt-subject". This makes the Azure Hub API ignore the subject and show the message as unmodeled data.

Code sample exhibiting the issue

const message = new Message(
          JSON.stringify({
            datetimeSignal,
            line,
            version: iotDataCollectorProperties.lastCollectFlightReports,
          }),
        );

        message.properties.add('dt-subject', 'logHistory');
        message.contentType = 'application/json';
        message.contentEncoding = 'utf-8';

        await azureIoTClientMqtt.sendEvent(message);

---

Analysing the code I found the code block where all message properties is added to the header with the prefix iothub-app

azure-iot-sdk-node/device/transport/http/src/http.ts

Line 177 in 2669521

httpHeaders[MESSAGE_PROP_HEADER_PREFIX + propItem.key] = propItem.value;

---

The same appear to be happening with sendEventBatch. Check this file:

azure-iot-sdk-node/device/transport/http/src/http.ts

Line 278 in 2669521

property += '\"' + MESSAGE_PROP_HEADER_PREFIX + propItem.key + '\":\"' + propItem.value + '\"';

---

I believe he should detect when the message property is dt-subject and ignore prefix, so the header should be only "dt-subject".

[anthonyvercolano]

Well, um, maybe. Since PnP is still in preview, it's questionable whether we should be special casing dt-subject.

If you look in some other later preview material, usually in helper samples, you would see this as $.sub

You would find that in 'c'. Note that 'c' ONLY supports MQTT. C sharp, much to my surprise, does seem to support what you want for HTTP.

So, why not utilize MQTT? You can use MQTT over websockets if you face firewall issues.

[ymoreiratiti]

In my scenario, I have a cronjob who downloads the log and sends it line by line. Currently, I'm using MQTT and doing an iteration for each file line, but I believe using the batch will be more network optimized.

[anthonyvercolano]

@ymoreiratiti I'm not understanding here.

What are your referring to when you say "batch"? How does "batch" interact with using HTTP?

[ymoreiratiti]

@anthonyvercolano for batch i'm refering to sendEventBatch.

You can send multiple messages with one request.

[anthonyvercolano]

Released