Add Rack instrumentation

adapters/rack/Gemfile

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+# frozen_string_literal: true
+
+# Copyright 2019 OpenTelemetry Authors
+#
+# SPDX-License-Identifier: Apache-2.0
+
+source 'https://rubygems.org'
+
+gemspec
+
+gem 'opentelemetry-api', path: '../../api'
+
+group :test do
+  gem 'opentelemetry-sdk', path: '../../sdk'
+end

adapters/rack/Rakefile

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+# frozen_string_literal: true
+
+# Copyright 2019 OpenTelemetry Authors
+#
+# SPDX-License-Identifier: Apache-2.0
+
+require 'bundler/gem_tasks'
+require 'rake/testtask'
+
+Rake::TestTask.new :test do |t|
+  t.libs << 'test'
+  t.libs << 'lib'
+  t.test_files = FileList['test/**/*_test.rb']
+end

adapters/rack/example/Gemfile

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+# frozen_string_literal: true
+
+source 'https://rubygems.org'
+
+gem 'rack'
+gem 'rack-test'
+gem 'opentelemetry-api', path: '../../../api'
+gem 'opentelemetry-sdk', path: '../../../sdk'

adapters/rack/example/trace_demonstration.rb

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+require 'rubygems'
+require 'bundler/setup'
+
+require 'opentelemetry/sdk'
+
+require 'rack'
+require_relative '../lib/opentelemetry/adapters/rack'
+
+# Set preferred tracer implementation:
+SDK = OpenTelemetry::SDK
+
+# global initialization:
+factory = OpenTelemetry.tracer_factory = SDK::Trace::TracerFactory.new
+factory.add_span_processor(
+  SDK::Trace::Export::SimpleSpanProcessor.new(
+    SDK::Trace::Export::ConsoleSpanExporter.new
+  )
+)
+
+# setup fake rack application:
+builder = Rack::Builder.new do
+  # can't use TracerMiddleware constant before calling Adapters::Rack.install:
+  #use OpenTelemetry::Adapters::Rack::Middlewares::TracerMiddleware
+end
+app = lambda { |env| [200, {'Content-Type' => 'text/plain'}, ['All responses are OK']] }
+builder.run app
+
+# demonstrate rack configuration options:
+config = {}
+config[:retain_middleware_names] = true
+config[:application] = builder
+config[:record_frontend_span] = true
+OpenTelemetry::Adapters::Rack.install(config)
+
+# integrate/activate tracing middleware:
+builder.use OpenTelemetry::Adapters::Rack::Middlewares::TracerMiddleware
+
+puts Rack::MockRequest.new(builder).get('/')

adapters/rack/lib/opentelemetry/adapters/rack.rb

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+# frozen_string_literal: true
+
+# Copyright 2020 OpenTelemetry Authors
+#
+# SPDX-License-Identifier: Apache-2.0
+
+module OpenTelemetry
+  module Adapters
+    module Rack
+      module_function
+
+      def install(config = {})
+        require_relative 'rack/adapter'
+        Rack::Adapter.install(config)
+      end
+
+      # Convenience method to access the nested module name
+      def name
+        Module.nesting[0].to_s
+      end
+
+      # Convenience method to access the adapter version
+      def version
+        VERSION
+      end
+    end
+  end
+end
+
+require_relative './rack/version'

adapters/rack/lib/opentelemetry/adapters/rack/adapter.rb

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+# frozen_string_literal: true
+
+# Copyright 2020 OpenTelemetry Authors
+#
+# SPDX-License-Identifier: Apache-2.0
+
+module OpenTelemetry
+  module Adapters
+    module Rack
+      class Adapter
+        class << self
+          attr_reader :config,
+                      :propagator
+
+          def install(config = {})
+            @config = config
+            @propagator = OpenTelemetry.tracer_factory.http_text_format
+
+            new.install
+          end
+
+          def tracer
+            @tracer ||= OpenTelemetry::tracer_factory.tracer(
+              Rack.name,
+              Rack.version
+            )
+          end
+
+          attr_accessor :installed
+          alias_method :installed?, :installed
+        end
+
+        def install
+          return :already_installed if self.class.installed?
+
+          require_relative 'middlewares/tracer_middleware'
+
+          retain_middleware_names if config[:retain_middleware_names]
+
+          self.class.installed = true
+        end
+
+        private
+
+        MissingApplicationError = Class.new(StandardError)
+
+        def config
+          self.class.config
+        end
+
+        # intercept all middleware-compatible calls, retain class name
+        def retain_middleware_names
+          next_middleware = config[:application]
+          raise MissingApplicationError unless next_middleware
+
+          while next_middleware
+            if next_middleware.respond_to?(:call)
+              next_middleware.singleton_class.class_eval do
+                alias_method :__call, :call
+
+                def call(env)
+                  env['RESPONSE_MIDDLEWARE'] = self.class.to_s
+                  __call(env)
+                end
+              end
+            end
+
+            next_middleware = next_middleware.instance_variable_defined?('@app') &&
+              next_middleware.instance_variable_get('@app')
+          end
+        end
+      end
+    end
+  end
+end
+
+require_relative '../rack'