add regex example and test

processor/baggage/README.md

@@ -31,7 +31,7 @@ To install the instrumentation, add the gem to your Gemfile:
 gem 'opentelemetry-processor-baggage'
 ```
 
-Then add the processor to an SDK's configuration:
+Then configure the span processor to copy all baggage entries:
 
 ```ruby
 require 'rubygems'
@@ -40,8 +40,11 @@ require 'bundler/setup'
 Bundler.require
 
 OpenTelemetry::SDK.configure do |c|
-  # Add the BaggageSpanProcessor to the collection of span processors
-  c.add_span_processor(OpenTelemetry::Processor::Baggage::BaggageSpanProcessor.new)
+  # Add the BaggageSpanProcessor to the collection of span processors and
+  # copy all baggage entries
+  c.add_span_processor(OpenTelemetry::Processor::Baggage::BaggageSpanProcessor.new(
+    OpenTelemetry::Processor::Baggage::ALLOW_ALL_BAGGAGE_KEYS
+  ))
 
   # Because the span processor list is no longer empty, the SDK will not use the
   # values in OTEL_TRACES_EXPORTER to instantiate exporters.
@@ -57,13 +60,21 @@ OpenTelemetry::SDK.configure do |c|
 end
 ```
 
-A predicate proc that determines what baggage entries are copied can be provided as a constructor parameter.
+Alternatively, you can provide a custom baggage key predicate to select which baggage keys you want to copy.
 
 For example, to only copy baggage entries that start with `my-key`:
 
 ```ruby
 OpenTelemetry::Processor::Baggage::BaggageSpanProcessor.new(
-  keyfilter: ->(key) { key.start_with?('my-key') }
+  ->(baggage_key) { baggage_key.start_with?('my-key') }
+)
+```
+
+For example, to only copy baggage entries that match the regex `^key.+`:
+
+```ruby
+OpenTelemetry::Processor::Baggage::BaggageSpanProcessor.new(
+  ->(baggage_key) { baggage_key.match?('^key.+') }
 )
 ```
 

processor/baggage/lib/opentelemetry/processor/baggage/baggage_span_processor.rb

@@ -10,8 +10,8 @@
 module OpenTelemetry
   module Processor
     module Baggage
-      # A regex that matches all Baggage keys.
-      ALLOW_ALL = '*'
+      # A baggage key predicate that allows all keys to be added to the span as attributes.
+      ALLOW_ALL_BAGGAGE_KEYS = ->(_) { true }
 
       # The BaggageSpanProcessor reads key/values stored in Baggage in the
       # starting span's parent context and adds them as attributes to the span.
@@ -31,7 +31,7 @@ module Baggage
       #   OpenTelemetry::SDK.configure do |c|
       #     # Add the BaggageSpanProcessor to the collection of span processors
       #     c.add_span_processor(OpenTelemetry::Processor::Baggage::BaggageSpanProcessor.new(
-      #       OpenTelemetry::Processor::Baggage::ALLOW_ALL)
+      #       OpenTelemetry::Processor::Baggage::ALLOW_ALL_BAGGAGE_KEYS)
       #     )
       #
       #     # Because the span processor list is no longer empty, the SDK will not use the
@@ -50,10 +50,10 @@ class BaggageSpanProcessor < OpenTelemetry::SDK::Trace::SpanProcessor
         # Create a new BaggageSpanProcessor that reads Baggage keys and values from the parent context
         # and adds them as attributes to the span.
         #
-        # @param [Regexp] baggage_key_regex A regular expression that matches Baggage keys to be added as span attributes.
-        #  If the regex is '*', all Baggage keys will be added as attributes.
-        def initialize(baggage_key_regex)
-          @baggage_key_regex = baggage_key_regex
+        # @param [lambda] baggage_key_predicate A lambda that takes a baggage key and returns true if
+        #  the key should be added to the span as an attribute, false otherwise.
+        def initialize(baggage_key_predicate)
+          @baggage_key_predicate = baggage_key_predicate
           super()
         end
 
@@ -66,15 +66,11 @@ def initialize(baggage_key_regex)
         def on_start(span, parent_context)
           return unless span.respond_to?(:add_attributes) && parent_context.is_a?(::OpenTelemetry::Context)
 
-          if @baggage_key_regex == ALLOW_ALL
-            span.add_attributes(::OpenTelemetry::Baggage.values(context: parent_context))
-          else
-            span.add_attributes(
-              ::OpenTelemetry::Baggage
-                .values(context: parent_context)
-                .select { |k, _v| @baggage_key_regex.match(k) }
-            )
-          end
+          span.add_attributes(
+            ::OpenTelemetry::Baggage
+              .values(context: parent_context)
+              .select { |k, _v| @baggage_key_predicate.call(k) }
+          )
         end
 
         # Called when a Span is ended, does nothing.

processor/baggage/test/opentelemetry/processor/baggage/baggage_span_processor_test.rb

@@ -13,7 +13,7 @@
 OpenTelemetry::SDK.configure do |c|
   # the baggage processor getting wired in for integration testing
   c.add_span_processor OpenTelemetry::Processor::Baggage::BaggageSpanProcessor.new(
-    OpenTelemetry::Processor::Baggage::ALLOW_ALL
+    OpenTelemetry::Processor::Baggage::ALLOW_ALL_BAGGAGE_KEYS
   )
 
   # use a simple processor and in-memory export for testing sent spans
@@ -28,10 +28,19 @@
 describe OpenTelemetry::Processor::Baggage::BaggageSpanProcessor do
   let(:processor) do
     OpenTelemetry::Processor::Baggage::BaggageSpanProcessor.new(
-      OpenTelemetry::Processor::Baggage::ALLOW_ALL
+      OpenTelemetry::Processor::Baggage::ALLOW_ALL_BAGGAGE_KEYS
+    )
+  end
+  let(:starts_with_processor) do
+    OpenTelemetry::Processor::Baggage::BaggageSpanProcessor.new(
+      ->(baggage_key) { baggage_key.start_with?('a') }
+    )
+  end
+  let(:regex_processor) do
+    OpenTelemetry::Processor::Baggage::BaggageSpanProcessor.new(
+      ->(baggage_key) { baggage_key.match?(/^b_ke.+/) }
     )
   end
-  let(:filtered_processor) { OpenTelemetry::Processor::Baggage::BaggageSpanProcessor.new('^a.key') }
   let(:span) { Minitest::Mock.new }
   let(:context_with_baggage) do
     OpenTelemetry::Baggage.build(context: OpenTelemetry::Context.empty) do |baggage|
@@ -105,11 +114,21 @@
     end
   end
 
-  describe 'with a keyfilter' do
+  describe 'with a starts_with key predicate' do
     it 'only adds attributes that pass the keyfilter' do
-      span.expect(:add_attributes, span, [{ 'a_key' => 'a_value', 'b_key' => 'b_value' }])
+      span.expect(:add_attributes, span, [{ 'a_key' => 'a_value' }])
 
-      processor.on_start(span, context_with_baggage)
+      starts_with_processor.on_start(span, context_with_baggage)
+
+      span.verify
+    end
+  end
+
+  describe 'with a regex key predicate' do
+    it 'only adds attributes that pass the keyfilter' do
+      span.expect(:add_attributes, span, [{ 'b_key' => 'b_value' }])
+
+      regex_processor.on_start(span, context_with_baggage)
 
       span.verify
     end