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2d6a15ac00
Added support for storing OTel span context in HAProxy transaction variables as an alternative to HTTP headers, enabled by the OTEL_USE_VARS compile flag. The new vars.c module implements variable-based context propagation through the HAProxy variable subsystem. Variable names are constructed from a configurable prefix and the OTel propagation key, with dots normalized to underscores for HAProxy variable name compatibility and denormalized back during retrieval. The module provides flt_otel_var_register() to pre-register variables at parse time, flt_otel_var_set() and flt_otel_vars_unset() to store and clear context key-value pairs in the txn scope, flt_otel_vars_get() to collect all variables matching a prefix into an otelc_text_map for context extraction, and flt_otel_vars_dump() for debug logging of all OTel variables. The inject/extract keywords in the scope parser now accept an optional "use-vars" argument alongside "use-headers", controlled by the new FLT_OTEL_CTX_USE_VARS flag. Both storage types can be used simultaneously on the same span context, allowing context to be propagated through both HTTP headers and variables. The scope runner in event.c was extended to handle variable-based context in parallel with headers: during extraction, it reads matching variables via flt_otel_vars_get() when FLT_OTEL_CTX_USE_VARS is set; during injection, it stores each propagation key as a variable via flt_otel_var_set(). The unused resource cleanup now also unsets context variables when removing failed extraction contexts. The filter attach callback registers and sets the sess.otel.uuid variable with the generated session UUID, making the trace identifier available to HAProxy log formats and ACL expressions. The feature is conditionally compiled: the OTEL_USE_VARS flag controls whether vars.c is included in the build and whether the "use-vars" keyword is available in the configuration parser. |
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