feat: Xray compliant ids (#840)

* Fixing XRay propagator null exception

* Add test for missing header

* Adding trace id generation to be compatible with aws xray

* Fix rubocop

* Moving xray trace to propagator gem

* Moving so it includes

* Adding some documentation and a couple of tests

* Feedback changes

* renaming file to match module

* Fixing include

* Move location

* rename var

Author: scar-lovevery

propagator/xray/README.md

@@ -23,6 +23,23 @@ gem install opentelemetry-propagator-xray
 
 Or, if you use [bundler][bundler-home], include `opentelemetry-propagator-xray` in your `Gemfile`.
 
+In your application:
+```
+require 'opentelemetry/propagator/xray'
+# Optional
+ENV['OTEL_PROPAGATORS'] ||= 'xray' # Or you can set this as an environment variable outside of the application
+```
+
+## To generate AWS XRay compliant IDs use the 'OpenTelemetry::AWSXRayTrace' module:
+```
+require 'opentelemetry/propagator/xray'
+
+OpenTelemetry::SDK.configure do |c|
+  c.id_generator = OpenTelemetry::Propagator::XRay::IDGenerator
+end
+```
+The propagator and ID generation are independent and do not need to be used in conjunction but can be.
+
 ## How can I get involved?
 
 The `opentelemetry-propagator-xray` gem source is [on github][repo-github], along with related gems including `opentelemetry-api` and `opentelemetry-sdk`.

propagator/xray/lib/opentelemetry/propagator/xray.rb

@@ -46,3 +46,4 @@ def text_map_propagator
 end
 
 require_relative './xray/version'
+require_relative './xray/id_generator'

propagator/xray/lib/opentelemetry/propagator/xray/id_generator.rb

@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+
+# Copyright The OpenTelemetry Authors
+#
+# SPDX-License-Identifier: Apache-2.0
+
+module OpenTelemetry
+  module Propagator
+    module XRay
+      # This module is intended to only be used as an override for how to generate IDs to be compliant with XRay
+      module IDGenerator
+        extend self
+
+        # Generates a valid trace identifier, a 16-byte string with at least one
+        # non-zero byte.
+        # AWS Docs: https://docs.aws.amazon.com/xray/latest/api/API_PutTraceSegments.html
+        # hi - 4 bytes timestamp, 4 bytes random (Mid)
+        # low - 8 bytes random.
+        # Since we include timestamp, impossible to be invalid.
+        # @return [bytes] a valid trace ID that is compliant with AWS XRay.
+        def generate_trace_id
+          time_hi = generate_time_bytes
+          mid_and_low = RANDOM.bytes(12)
+          time_hi << mid_and_low
+        end
+
+        # Generates a valid span identifier, an 8-byte string with at least one
+        # non-zero byte.
+        #
+        # @return [bytes] a valid span ID.
+        def generate_span_id
+          OpenTelemetry::Trace.generate_span_id
+        end
+
+        private
+
+        # Random number generator for generating IDs. This is an object that can
+        # respond to `#bytes` and uses the system PRNG. The current logic is
+        # compatible with Ruby 2.5 (which does not implement the `Random.bytes`
+        # class method) and with Ruby 3.0+ (which deprecates `Random::DEFAULT`).
+        # When we drop support for Ruby 2.5, this can simply be replaced with
+        # the class `Random`.
+        #
+        # @return [#bytes]
+        RANDOM = Random.respond_to?(:bytes) ? Random : Random::DEFAULT
+
+        # Seconds since epoch converted to 4 bytes in big-endian order.
+        def generate_time_bytes
+          [Time.now.to_i].pack('N')
+        end
+      end
+    end
+  end
+end

propagator/xray/test/aws_xray_trace_test.rb

@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+require 'date'
+require 'test_helper'
+
+describe OpenTelemetry::Trace::SpanContext do
+  let(:id_generator) { OpenTelemetry::Propagator::XRay::IDGenerator }
+
+  describe 'generate trace id in the correct format' do
+    it 'must generate 16 in length' do
+      trace_id = id_generator.generate_trace_id
+      _(trace_id.length).must_equal(16)
+    end
+    it 'first 4 bytes should be a valid epoch date' do
+      trace_id = id_generator.generate_trace_id
+      # Convert to hex
+      hex = trace_id[0..3].unpack1('H*')
+      # Convert to int
+      time_int = hex.to_i(16)
+      # Convert to datetime
+      begin
+        date = Time.at(time_int).to_datetime
+      rescue ArgumentError
+        date = nil
+      end
+      # Make sure it's valid
+      _(date).wont_be_nil
+    end
+    it 'generate_span_id still works' do
+      trace_id = id_generator.generate_span_id
+      # Make sure it's valid
+      _(trace_id).wont_be_nil
+    end
+  end
+end