trackDependencyData id format validation breaks W3C correlation with plain spanId

[szelpe]

When using trackDependencyData with W3C distributed tracing mode, the SDK blindly appends a trailing period to any id that doesn't already end with one. This breaks correlation when passing a plain W3C spanId.

Current behavior ajax.ts

// Hack since expected format in w3c mode is |abc.def.
// Non-w3c format is |abc.def
// @todo Remove if better solution is available, e.g. handle in portal
if (dependency.id[dependency.id.length - 1] !== ".") {
    dependency.id += ".";
}

The code only checks if the last character is a period, not whether the ID is actually in the expected |{traceId}.{spanId} format.

Problem

When manually tracking dependencies with trackDependencyData using a plain W3C spanId:

• Input: id: "861bce51737e3ba6" (16-char hex spanId)
• Result: "861bce51737e3ba6." (spanId with trailing period)

This doesn't match the server-side parent_id (which is the plain spanId from the W3C traceparent header), breaking parent-child correlation in the waterfall view.

Expected behavior

The SDK should only append a period if the ID matches the legacy |{traceId}.{spanId} format:

const legacyIdPattern = /^\|[a-f0-9]+\.[a-f0-9]+$/i;
if (legacyIdPattern.test(dependency.id)) {
    dependency.id += ".";
}

This would:

• |abc123.def456 → |abc123.def456. (legacy format, add period)
• 861bce51737e3ba6 → 861bce51737e3ba6 (plain spanId, leave alone)

Reproduction

appInsights.trackDependencyData({
    id: "861bce51737e3ba6", // plain W3C spanId
    name: "GET /api/user",
    duration: 100,
    success: true,
    responseCode: 200,
    type: "HTTP",
    target: "api.example.com"
});
// Results in id: "861bce51737e3ba6." which doesn't correlate with server parent_id

Environment

• SDK version: latest
• distributedTracingMode: W3C

Related

• PR fix w3c correlation #1213 introduced this behavior
• Issue Id format changes in W3C mode #1136 discussed ID format changes

[MSNev]

This is not a bug, it is the required behavior for the backend when sending the event to the backend

|abc123.def456 → |abc123.def456. (legacy format, add period)

The correct format for a full W3C "id" for the event is
|<traceId>.<spanId>

[szelpe]

This is not a bug, it is the required behavior for the backend when sending the event to the backend

Thanks for the reply, @MSNev!

Unfortunately, I couldn't find any mention of that requirement in the docs or samples:

• API-reference
• Sample in the README

I used a random id:

appInsights.trackDependencyData({
    id: "861bce51737e3ba6",
    name: "GET /api/user"
});

And I was surprised to find that when viewing the dependency in the portal, a period was appended: 861bce51737e3ba6.

I set the child dependency's parent id to 861bce51737e3ba6 (in another service), but it didn't appear as a child in the waterfall view because of the trailing period.

I spent hours debugging why there was a trailing period, and could only resolve the issue by looking at the source code.

[szelpe]

There's even an issue from 2019 stating this is no longer a requirement: #1136

[MSNev]

That link issue was not raised by anyone from the server team and the link PR within that issue is the PR that introduced the change.

Basically the "id" is NOT the id used for correlation from the Ajax request (ie. this is not the code that populates the traceparent header), but this if "how" we send this information to the backend "Azure Monitor" service.

[aimbrenda]

It is probably you breaking the correlation, breaking the relation parent child with the backend you sent the request, because you replace the id.