Feat: Add custom getters to common (open-telemetry#1006)

Co-authored-by: Matthew Wear <matthew.wear@gmail.com>

common/lib/opentelemetry/common.rb

@@ -6,6 +6,7 @@
 
 require 'opentelemetry'
 require 'opentelemetry/common/http'
+require 'opentelemetry/common/propagation'
 require 'opentelemetry/common/utilities'
 require 'opentelemetry/common/version'
 

common/lib/opentelemetry/common/propagation.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+# Copyright The OpenTelemetry Authors
+#
+# SPDX-License-Identifier: Apache-2.0
+
+require_relative './propagation/rack_env_getter'
+require_relative './propagation/symbol_key_getter'
+
+module OpenTelemetry
+  module Common
+    # Propagation contains common helpers for context propagation.
+    module Propagation
+      extend self
+
+      RACK_ENV_GETTER = RackEnvGetter.new
+      SYMBOL_KEY_GETTER = SymbolKeyGetter.new
+      private_constant :RACK_ENV_GETTER, :SYMBOL_KEY_GETTER
+
+      # Returns a {RackEnvGetter} instance suitable for reading values from a
+      # Rack environment.
+      def rack_env_getter
+        RACK_ENV_GETTER
+      end
+
+      # Returns a {SymbolKeyGetter} instance for reading values from a
+      # symbol keyed hash.
+      def symbol_key_getter
+        SYMBOL_KEY_GETTER
+      end
+    end
+  end
+end

common/lib/opentelemetry/common/propagation/rack_env_getter.rb

@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+
+# Copyright The OpenTelemetry Authors
+#
+# SPDX-License-Identifier: Apache-2.0
+
+module OpenTelemetry
+  module Common
+    module Propagation
+      # The RackEnvGetter class provides a common methods for reading
+      # keys from a rack environment. It abstracts away the rack-normalization
+      # process so that keys can be looked up without having to transform them
+      # first. With this class you can get +traceparent+ instead of
+      # +HTTP_TRACEPARENT+
+      class RackEnvGetter
+        # Converts key into a rack-normalized key and reads it from the carrier.
+        # Useful for extract operations.
+        def get(carrier, key)
+          carrier[to_rack_key(key)] || carrier[key]
+        end
+
+        # Reads all keys from a carrier and converts them from the rack-normalized
+        # form to the original. The resulting keys will be lowercase and
+        # underscores will be replaced with dashes.
+        def keys(carrier)
+          carrier.keys.map(&method(:from_rack_key))
+        end
+
+        private
+
+        def to_rack_key(key)
+          ret = 'HTTP_' + key
+          ret.tr!('-', '_')
+          ret.upcase!
+          ret
+        end
+
+        def from_rack_key(key)
+          start = key.start_with?('HTTP_') ? 5 : 0
+          ret = key[start..-1]
+          ret.tr!('_', '-')
+          ret.downcase!
+          ret
+        end
+      end
+    end
+  end
+end

common/lib/opentelemetry/common/propagation/symbol_key_getter.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+# Copyright The OpenTelemetry Authors
+#
+# SPDX-License-Identifier: Apache-2.0
+
+module OpenTelemetry
+  module Common
+    module Propagation
+      # The SymbolKeyGetter class provides a common method for reading
+      # symbol keys from a hash.
+      class SymbolKeyGetter
+        # Converts key into a symbol and reads it from the carrier.
+        # Useful for extract operations.
+        def get(carrier, key)
+          carrier[key.to_sym]
+        end
+
+        # Reads all keys from a carrier
+        def keys(carrier)
+          carrier.keys.map(&:to_s)
+        end
+      end
+    end
+  end
+end

common/test/opentelemetry/common/propagation/rack_env_getter_test.rb

@@ -0,0 +1,45 @@
+# frozen_string_literal: true
+
+# Copyright The OpenTelemetry Authors
+#
+# SPDX-License-Identifier: Apache-2.0
+
+require 'test_helper'
+
+describe OpenTelemetry::Common::Propagation::RackEnvGetter do
+  let(:getter) do
+    OpenTelemetry::Context::Propagation::RackEnvGetter.new
+  end
+
+  let(:carrier) do
+    {
+      'HTTP_TRACEPARENT' => 'tp',
+      'HTTP_TRACESTATE' => 'ts',
+      'HTTP_X_SOURCE_ID' => '123',
+      'rack.hijack?' => true
+    }
+  end
+
+  describe '#get' do
+    it 'reads key from carrier' do
+      _(getter.get(carrier, 'traceparent')).must_equal('tp')
+      _(getter.get(carrier, 'tracestate')).must_equal('ts')
+      _(getter.get(carrier, 'x-source-id')).must_equal('123')
+      _(getter.get(carrier, 'rack.hijack?')).must_equal(true)
+    end
+
+    it 'returns nil for non-existent key' do
+      _(getter.get(carrier, 'not-here')).must_be_nil
+    end
+  end
+
+  describe '#keys' do
+    it 'returns carrier keys' do
+      _(getter.keys(carrier)).must_equal(%w[traceparent tracestate x-source-id rack.hijack?])
+    end
+
+    it 'returns empty array for empty carrier' do
+      _(getter.keys({})).must_equal([])
+    end
+  end
+end

common/test/opentelemetry/common/propagation/symbol_key_getter_test.rb

@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+# Copyright The OpenTelemetry Authors
+#
+# SPDX-License-Identifier: Apache-2.0
+
+require 'test_helper'
+
+describe OpenTelemetry::Common::Propagation::SymbolKeyGetter do
+  let(:symbol_key_getter) { OpenTelemetry::Common::Propagation::SymbolKeyGetter.new }
+  let(:carrier) { { foo: 'bar' } }
+
+  describe '#get' do
+    it 'retrieves the value' do
+      _(symbol_key_getter.get(carrier, 'foo')).must_equal('bar')
+    end
+  end
+
+  describe '#keys' do
+    it 'returns all the keys as strings' do
+      _(symbol_key_getter.keys(carrier)).must_equal(['foo'])
+    end
+  end
+end