fix: Fix the array encoding length of datadog version 05 exporter

[glynnmccabe]

Fixes the array encoding length used for datadog version 05 api exporting. This is causing #970

[linux-foundation-easycla]

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• ✅ login: glynnmccabe / name: Glynn (fb2154a)

[codecov]

Codecov Report

Patch coverage: 100.0% and project coverage change: -0.1 ⚠️

Comparison is base (675de34) 69.9% compared to head (2a00fca) 69.9%.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1002     +/-   ##
=======================================
- Coverage   69.9%   69.9%   -0.1%     
=======================================
  Files        116     116             
  Lines       9027    9027             
=======================================
- Hits        6316    6315      -1     
- Misses      2711    2712      +1     

Impacted Files	Coverage Δ
opentelemetry-datadog/src/exporter/mod.rs	25.8% <ø> (ø)
opentelemetry-datadog/src/exporter/model/mod.rs	78.5% <ø> (ø)
opentelemetry-datadog/src/exporter/model/v05.rs	85.8% <100.0%> (ø)

... and 1 file with indirect coverage changes

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[djc]

I feel this is like #903 in that we really should be using some derive-based encoding of types to send Datadog messages, instead of the raw MessagePack encoding that we're doing here.

[glynnmccabe]

In this case it seems that the span array is always 12 elements long regardless of other improvements we might want, or am I missing something? #903 is what broke this for v05

[TommyCpp]

Another issue is we don't have access to Datadog backend to verify any fix so it's tricky

[glynnmccabe]

Running the datadog agent locally the current version will not accept traces with a 400 error and will accept them with the change.

There is also a test agent which also will not accept traces with a value that is not 12 - https://github.com/DataDog/dd-apm-test-agent/blob/cc71f96050a79bbe114b9e82005d92a7a8ca1e4f/ddapm_test_agent/trace.py#L304

[hdost]

Running the datadog agent locally the current version will not accept traces with a 400 error and will accept them with the change.

There is also a test agent which also will not accept traces with a value that is not 12 - https://github.com/DataDog/dd-apm-test-agent/blob/cc71f96050a79bbe114b9e82005d92a7a8ca1e4f/ddapm_test_agent/trace.py#L304

I've tried running the example against the test agent and I get failures even with your patch.
What are you using to test?

[glynnmccabe]

Running the datadog agent locally the current version will not accept traces with a 400 error and will accept them with the change.
There is also a test agent which also will not accept traces with a value that is not 12 - https://github.com/DataDog/dd-apm-test-agent/blob/cc71f96050a79bbe114b9e82005d92a7a8ca1e4f/ddapm_test_agent/trace.py#L304

I've tried running the example against the test agent and I get failures even with your patch. What are you using to test?

Datadog agent 7.43.1, although I have used the test agent previously.

Are the failures you see related to headers? The test agent expects some headers that this exporter doesn't send, but don't seem to be required by the actual agent. If so turning off the invariant checks listed here would fix that. https://github.com/DataDog/dd-apm-test-agent#trace-invariant-checks

[TommyCpp]

Looks good. Thanks for the fix!