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# frozen_string_literal: true
# Released under the MIT License.
# Copyright, 2021-2025, by Samuel Williams.
require_relative "config"
require_relative "context"
module Traces
# The backend implementation is responsible for recording and reporting traces.
module Backend
end
# Capture the current trace context for remote propagation.
#
# This is a default implementation, which can be replaced by the backend.
#
# You should prefer to use the new `Traces.current_context` family of methods.
#
# @returns [Object] The current trace context.
def self.trace_context
nil
end
# Whether there is an active trace context.
#
# This is a default implementation, which can be replaced by the backend.
#
# @returns [Boolean] Whether there is an active trace.
def self.active?
!!self.trace_context
end
# Capture the current trace context for local propagation between execution contexts.
#
# This method returns the current trace context that can be safely passed between threads, fibers, or other execution contexts within the same process.
#
# The returned object is opaque, in other words, you should not make assumptions about its structure.
#
# This is a default implementation, which can be replaced by the backend.
#
# @returns [Context | Nil] The current trace context, or nil if no active trace.
def self.current_context
trace_context
end
# Execute a block within a specific trace context for local execution.
#
# This method is designed for propagating trace context between execution contexts within the same process (threads, fibers, etc.). It temporarily switches to the specified trace context for the duration of the block execution, then restores the previous context.
#
# When called without a block, permanently switches to the specified context. This enables manual context management for scenarios where automatic restoration isn't desired.
#
# This is a default implementation, which can be replaced by the backend.
#
# @parameter context [Context] A trace context obtained from `Traces.current_context`.
# @yields {...} If a block is given, the block is executed within the specified trace context.
def self.with_context(context)
if block_given?
# This implementation is not ideal but the best we can do with the current interface.
previous_context = self.trace_context
begin
self.trace_context = context
yield
ensure
self.trace_context = previous_context
end
else
self.trace_context = context
end
end
# Inject trace context into a headers hash for distributed propagation.
#
# This method adds W3C Trace Context headers (traceparent, tracestate) and W3C Baggage headers to the provided headers hash, enabling distributed tracing across service boundaries. The headers hash is mutated in place.
#
# This is a default implementation, which can be replaced by the backend.
#
# @parameter headers [Hash] The headers object to mutate with trace context headers.
# @parameter context [Context] A trace context, or nil to use current context.
# @returns [Hash | Nil] The headers hash, or nil if no context is available.
def self.inject(headers = nil, context = nil)
context ||= self.trace_context
if context
headers ||= Hash.new
context.inject(headers)
else
headers = nil
end
return headers
end
# Extract trace context from headers for distributed propagation.
#
# The returned object is opaque, in other words, you should not make assumptions about its structure.
#
# This is a default implementation, which can be replaced by the backend.
#
# @parameter headers [Hash] The headers object containing trace context.
# @returns [Context, nil] The extracted trace context, or nil if no valid context found.
def self.extract(headers)
Context.extract(headers)
end
Config::DEFAULT.require_backend
end
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