fix!: refactor propagators to add #fields

api/lib/opentelemetry.rb

@@ -71,9 +71,6 @@ def baggage
 
   # @return [Context::Propagation::Propagator] a propagator instance
   def propagation
-    @propagation ||= Context::Propagation::Propagator.new(
-      Context::Propagation::NoopInjector.new,
-      Context::Propagation::NoopExtractor.new
-    )
+    @propagation ||= Context::Propagation::NoopTextMapPropagator.new
   end
 end

api/lib/opentelemetry/baggage/propagation.rb

@@ -5,32 +5,23 @@
 # SPDX-License-Identifier: Apache-2.0
 
 require 'opentelemetry/baggage/propagation/context_keys'
-require 'opentelemetry/baggage/propagation/text_map_injector'
-require 'opentelemetry/baggage/propagation/text_map_extractor'
+require 'opentelemetry/baggage/propagation/text_map_propagator'
 
 module OpenTelemetry
   module Baggage
-    # The Baggage::Propagation module contains injectors and
-    # extractors for sending and receiving baggage over the wire
+    # The Baggage::Propagation module contains a text map propagator for
+    # sending and receiving baggage over the wire.
     module Propagation
       extend self
 
-      BAGGAGE_KEY = 'baggage'
-      TEXT_MAP_EXTRACTOR = TextMapExtractor.new
-      TEXT_MAP_INJECTOR = TextMapInjector.new
+      TEXT_MAP_PROPAGATOR = TextMapPropagator.new
 
-      private_constant :BAGGAGE_KEY, :TEXT_MAP_INJECTOR, :TEXT_MAP_EXTRACTOR
+      private_constant :TEXT_MAP_PROPAGATOR
 
-      # Returns an extractor that extracts context using the W3C Baggage
-      # format
-      def text_map_injector
-        TEXT_MAP_INJECTOR
-      end
-
-      # Returns an injector that injects context using the W3C Baggage
-      # format
-      def text_map_extractor
-        TEXT_MAP_EXTRACTOR
+      # Returns a text map propagator that propagates context using the
+      # W3C Baggage format.
+      def text_map_propagator
+        TEXT_MAP_PROPAGATOR
       end
     end
   end

api/lib/opentelemetry/baggage/propagation/text_map_propagator.rb

@@ -0,0 +1,109 @@
+# frozen_string_literal: true
+
+# Copyright The OpenTelemetry Authors
+#
+# SPDX-License-Identifier: Apache-2.0
+
+require 'cgi'
+
+module OpenTelemetry
+  module Baggage
+    module Propagation
+      # Propagates baggage using the W3C Baggage format
+      class TextMapPropagator
+        # Maximums according to W3C Baggage spec
+        MAX_ENTRIES = 180
+        MAX_ENTRY_LENGTH = 4096
+        MAX_TOTAL_LENGTH = 8192
+
+        BAGGAGE_KEY = 'baggage'
+        FIELDS = [BAGGAGE_KEY].freeze
+
+        private_constant :BAGGAGE_KEY, :FIELDS, :MAX_ENTRIES, :MAX_ENTRY_LENGTH, :MAX_TOTAL_LENGTH
+
+        # Inject in-process baggage into the supplied carrier.
+        #
+        # @param [Carrier] carrier The mutable carrier to inject baggage into
+        # @param [Context] context The context to read baggage from
+        # @param [optional Setter] setter If the optional setter is provided, it
+        #   will be used to write context into the carrier, otherwise the default
+        #   text map setter will be used.
+        def inject(carrier, context: Context.current, setter: Context::Propagation.text_map_setter)
+          baggage = OpenTelemetry.baggage.raw_entries(context: context)
+
+          return if baggage.nil? || baggage.empty?
+
+          encoded_baggage = encode(baggage)
+          setter.set(carrier, BAGGAGE_KEY, encoded_baggage) unless encoded_baggage&.empty?
+          nil
+        end
+
+        # Extract remote baggage from the supplied carrier.
+        # If extraction fails, the original context will be returned
+        #
+        # @param [Carrier] carrier The carrier to get the header from
+        # @param [optional Context] context Context to be updated with the baggage
+        #   extracted from the carrier. Defaults to +Context.current+.
+        # @param [optional Getter] getter If the optional getter is provided, it
+        #   will be used to read the header from the carrier, otherwise the default
+        #   text map getter will be used.
+        #
+        # @return [Context] context updated with extracted baggage, or the original context
+        #   if extraction fails
+        def extract(carrier, context: Context.current, getter: Context::Propagation.text_map_getter)
+          header = getter.get(carrier, BAGGAGE_KEY)
+
+          entries = header.gsub(/\s/, '').split(',')
+
+          OpenTelemetry.baggage.build(context: context) do |builder|
+            entries.each do |entry|
+              # Note metadata is currently unused in OpenTelemetry, but is part
+              # the W3C spec where it's referred to as properties. We preserve
+              # the properties (as-is) so that they can be propagated elsewhere.
+              kv, meta = entry.split(';', 2)
+              k, v = kv.split('=').map!(&CGI.method(:unescape))
+              builder.set_value(k, v, metadata: meta)
+            end
+          end
+        rescue StandardError => e
+          OpenTelemetry.logger.debug "Error extracting W3C baggage: #{e.message}"
+          context
+        end
+
+        # Returns the predefined propagation fields. If your carrier is reused, you
+        # should delete the fields returned by this method before calling +inject+.
+        #
+        # @return [Array<String>] a list of fields that will be used by this propagator.
+        def fields
+          FIELDS
+        end
+
+        private
+
+        def encode(baggage)
+          result = +''
+          encoded_count = 0
+          baggage.each_pair do |key, entry|
+            break unless encoded_count < MAX_ENTRIES
+
+            encoded_entry = encode_value(key, entry)
+            next unless encoded_entry.size <= MAX_ENTRY_LENGTH &&
+                        encoded_entry.size + result.size <= MAX_TOTAL_LENGTH
+
+            result << encoded_entry << ','
+            encoded_count += 1
+          end
+          result.chop!
+        end
+
+        def encode_value(key, entry)
+          result = +"#{CGI.escape(key.to_s)}=#{CGI.escape(entry.value.to_s)}"
+          # We preserve metadata recieved on extract and assume it's already formatted
+          # for transport. It's sent as-is without further processing.
+          result << ";#{entry.metadata}" if entry.metadata
+          result
+        end
+      end
+    end
+  end
+end

api/lib/opentelemetry/context/propagation.rb

@@ -4,18 +4,48 @@
 #
 # SPDX-License-Identifier: Apache-2.0
 
-require 'opentelemetry/context/propagation/composite_propagator'
-require 'opentelemetry/context/propagation/noop_extractor'
-require 'opentelemetry/context/propagation/noop_injector'
-require 'opentelemetry/context/propagation/propagator'
+require 'opentelemetry/context/propagation/composite_text_map_propagator'
+require 'opentelemetry/context/propagation/noop_text_map_propagator'
+require 'opentelemetry/context/propagation/rack_env_getter'
 require 'opentelemetry/context/propagation/text_map_getter'
+require 'opentelemetry/context/propagation/text_map_propagator'
 require 'opentelemetry/context/propagation/text_map_setter'
-require 'opentelemetry/context/propagation/rack_env_getter'
 
 module OpenTelemetry
   class Context
     # The propagation module contains APIs and utilities to interact with context
     # and propagate across process boundaries.
+    #
+    # The API implicitly defines 3 interfaces: TextMapPropagator, TextMapInjector
+    # and TextMapExtractor. Concrete implementations of TextMapPropagator are
+    # provided. Custom text map propagators can leverage these implementations
+    # or simply implement the expected interface. The interfaces are described
+    # below.
+    #
+    # The TextMapPropagator interface:
+    #
+    #    inject(carrier, context:, setter:)
+    #    extract(carrier, context:, getter:) -> Context
+    #    fields -> Array<String>
+    #
+    # The TextMapInjector interface:
+    #
+    #    inject(carrier, context:, setter:)
+    #    fields -> Array<String>
+    #
+    # The TextMapExtractor interface:
+    #
+    #    extract(carrier, context:, getter:) -> Context
+    #
+    # The API provides 3 TextMapPropagator implementations:
+    # - A default NoopTextMapPropagator that implements +inject+ and +extract+
+    #   methods as no-ops. Its +fields+ method returns an empty list.
+    # - A TextMapPropagator that composes an Injector and an Extractor. Its
+    #   +fields+ method delegates to the provided Injector.
+    # - A CompositeTextMapPropagator that wraps either a list of text map
+    #   propagators or a list of Injectors and a list of Extractors. Its
+    #   +fields+ method returns the union of fields returned by the Injectors
+    #   it wraps.
     module Propagation
       extend self