NEED FEEDBACK FROM MAINTAINERS Addressing issue #4793 - allow app to control b3-propagator sampling decision when no sampling state in carrier from remote #4794
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vitaly-krugl
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vitaly-krugl
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vitaly-krugl
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Oct 31, 2025
| if single_header: | ||
| # The b3 spec calls for the sampling state to be | ||
| # "deferred", which is unspecified. This concept does not | ||
| # translate to SpanContext, so we set it as recorded. |
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The b3 spec calls for the sampling state to be deferred "to the receiver" whenever remote doesn't supply it. This pull request facilitates allowing the receiver to make the decision in this scenario.
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…n't allow the receiver to make sampling decision when X-B3-Sampled header is absent. No unit test update yet.
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Description
WORK IN PROGRESS - requesting acceptance feasibility feedback from maintainers before proceeding with additional unit tests.
Fixes # 4793
opentelemetry-propagator-b3 doesn't allow the receiver to make sampling decision when X-B3-Sampled header is absent.
This issue is somewhat unique to Zipkin/B3 because it treats sampling state in HTTP headers as optional. Hence, the solution is specific to B3. By contrast, the sampling state is required in W3C Trace Context, and no such solution is necessary for W3C support.
The Zipkin/B3 protocol - https://github.com/openzipkin/b3-propagation - leaves the sampling decision up to the receiver whenever it doesn't receive an explicit sampling state from remote in the carrier:
However, opentelemetry-propagator-b3 incorrectly hard-codes absent sampling state to OFF, not giving the application an opportunity to make this decision. The class
B3MultiFormatdoes not provide the means for an application to specify its preference for the default behavior when sampling state is not received from remoteType of change
Please delete options that are not relevant.
How Has This Been Tested?
Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration
Does This PR Require a Contrib Repo Change?
Checklist: