B3 Propagator doesn't handle 64-bit TraceIDs

[Aneurysm9]

The B3 spec allows for both 64-bit and 128-bit TraceIDs, but does not specify how to handle interop between systems that produce/expect different length IDs.

The Otel-Go B3 propagator uses core.TraceIDFromHex() which requires a hex-encoded TraceID be 32 hex digits.

Should we left-pad incoming TraceID values in the B3 propagator prior to decoding, or should we take another approach?

[jmacd]

@MikeGoldsmith @codeboten would you comment? I believe you've studied this.

[lizthegrey]

Please escalate this to the Spec SIG, as we need to consistently handle this across all of OTel.

[Aneurysm9]

I actually think that the spec provides enough to consistently handle the issue, so I'll not open an issue against the spec repo, but I will add it to the agenda for the next Spec SIG meeting so we can discuss.

I think that between the trace API spec declaring that "[t]he OpenTelemetry SpanContext representation conforms to the w3c TraceContext specification" and the w3c interop guidance stating that "[s]horter identifiers SHOULD be left padded with zeros when converted to 16 bytes trace-id", the correct approach is clear.

After surveying the other OTel implementations, I found the following that exhibit the same issue when receiving 64-bit B3 TraceID values:

• opentelemetry-js
• opentelemetry-swift (invoked here) appears to expect the TraceID to be 128 bits.

The following implementations left-pad the TraceID:

• opentelemetry-java (contrib)
• opentelemetry-dotnet and the single header version

The following implementations do not validate the TraceID length and parse as received from hex to integers:

• opentelemetry-rust
• opentelemetry-python

The opentelemetry-erlang implementation converts from hex to integer after validating the incoming hex is 16 or 32 digits.

The remaining implementations (PHP, Ruby, C++) do not appear to provide B3 propagators.

[SergeyKanzhelev]

Some relevant discussion: w3c/trace-context#349 I agree, we need consistency on whether short Trace-ID should be accepted

[tedsuo]

+1 for left padding with zeros