Module: Datadog::Tracing::Propagation::HTTP

Defined in:
lib/datadog/tracing/propagation/http.rb

Overview

Propagation::HTTP helps extracting and injecting HTTP headers.

Constant Summary collapse

PROPAGATION_STYLES = 
{
  Configuration::Ext::Distributed::PROPAGATION_STYLE_B3 => Distributed::Headers::B3,
  Configuration::Ext::Distributed::PROPAGATION_STYLE_B3_SINGLE_HEADER => Distributed::Headers::B3Single,
  Configuration::Ext::Distributed::PROPAGATION_STYLE_DATADOG => Distributed::Headers::Datadog
}.freeze

Class Method Summary collapse

Class Method Details

.extract(env) ⇒ Object

extract returns trace headers containing the span ID, trace ID and sampling priority defined in env.



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# File 'lib/datadog/tracing/propagation/http.rb', line 62

def self.extract(env)
  trace_digest = nil
  dd_trace_digest = nil

  Datadog.configuration.tracing.distributed_tracing.propagation_extract_style.each do |style|
    propagator = PROPAGATION_STYLES[style]
    next if propagator.nil?

    # Extract trace headers
    # DEV: `propagator.extract` will return `nil`, where `Propagation::HTTP#extract` will not
    begin
      extracted_trace_digest = propagator.extract(env)
    rescue => e
      Datadog.logger.error(
        'Error extracting propagated trace headers from the environment. ' \
        "Cause: #{e} Location: #{Array(e.backtrace).first}"
      )
    end

    # Skip this style if no valid headers were found
    next if extracted_trace_digest.nil?

    # Keep track of the Datadog extract trace headers, we want to return
    #   this one if we have one
    if extracted_trace_digest && style == Configuration::Ext::Distributed::PROPAGATION_STYLE_DATADOG
      dd_trace_digest = extracted_trace_digest
    end

    # No previously extracted trace headers, use the one we just extracted
    if trace_digest.nil?
      trace_digest = extracted_trace_digest
    else
      unless trace_digest.trace_id == extracted_trace_digest.trace_id \
              && trace_digest.span_id == extracted_trace_digest.span_id
        # Return an empty/new trace headers if we have a mismatch in values extracted
        msg = "#{trace_digest.trace_id} != #{extracted_trace_digest.trace_id} && " \
              "#{trace_digest.span_id} != #{extracted_trace_digest.span_id}"
        Datadog.logger.debug(
          "Cannot extract trace headers from HTTP: extracted trace headers differ, #{msg}"
        )
        # DEV: This will return from `self.extract` not this `each` block
        return TraceDigest.new
      end
    end
  end

  # Return the extracted trace headers if we found one or else a new empty trace headers
  # Always return the Datadog trace headers if one exists since it has more
  #   information than the B3 headers e.g. origin, expanded priority
  #   sampling values, etc
  dd_trace_digest || trace_digest || nil
end

.inject!(digest, env) ⇒ Object

inject! populates the env with span ID, trace ID and sampling priority

DEV-2.0: inject! should work without arguments, injecting the active_trace's digest DEV-2.0: and returning a new Hash with the injected headers. DEV-2.0: inject! should also accept either a trace or a digest, as a trace DEV-2.0: argument is the common use case, but also allows us to set error tags in the trace DEV-2.0: if needed. DEV-2.0: Ideally, we'd have a separate stream to report tracer errors and never DEV-2.0: touch the active span.



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# File 'lib/datadog/tracing/propagation/http.rb', line 35

def self.inject!(digest, env)
  # Prevent propagation from being attempted if trace headers provided are nil.
  if digest.nil?
    Datadog.logger.debug(
      'Cannot inject trace headers into env to propagate over HTTP: trace headers are nil.'.freeze
    )
    return
  end

  digest = digest.to_digest if digest.is_a?(TraceOperation)

  # Inject all configured propagation styles
  Datadog.configuration.tracing.distributed_tracing.propagation_inject_style.each do |style|
    propagator = PROPAGATION_STYLES[style]
    begin
      propagator.inject!(digest, env) unless propagator.nil?
    rescue => e
      Datadog.logger.error(
        'Error injecting propagated trace headers into the environment. ' \
        "Cause: #{e} Location: #{Array(e.backtrace).first}"
      )
    end
  end
end