fix: httpx instrumentation trace context propagation

instrumentation/httpx/Appraisals

@@ -7,7 +7,3 @@
 appraise 'httpx-1' do
   gem 'httpx', '~> 1.0'
 end
-
-appraise 'httpx-0' do
-  gem 'httpx', '~> 0.24'
-end

instrumentation/httpx/lib/opentelemetry/instrumentation/httpx/plugin.rb

@@ -10,83 +10,114 @@ module HTTPX
       module Plugin
         # Instruments around HTTPX's request/response lifecycle in order to generate
         # an OTEL trace.
-        class RequestTracer
-          # Constant for the HTTP status range
-          HTTP_STATUS_SUCCESS_RANGE = (100..399)
+        module RequestTracer
+          module_function
+
+          # initializes tracing on the +request+.
+          def call(request)
+            span = nil
+
+            # request objects are reused, when already buffered requests get rerouted to a different
+            # connection due to connection issues, or when they already got a response, but need to
+            # be retried. In such situations, the original span needs to be extended for the former,
+            # while a new is required for the latter.
+            request.on(:idle) do
+              span = nil
+            end
+            # the span is initialized when the request is buffered in the parser, which is the closest
+            # one gets to actually sending the request.
+            request.on(:headers) do
+              next if span
+
+              span = initialize_span(request)
+            end
+
+            request.on(:response) do |response|
+              unless span
+                next unless response.is_a?(::HTTPX::ErrorResponse) && response.error.respond_to?(:connection)
 
-          def initialize(request)
-            @request = request
+                # handles the case when the +error+ happened during name resolution, which means
+                # that the tracing start point hasn't been triggered yet; in such cases, the approximate
+                # initial resolving time is collected from the connection, and used as span start time,
+                # and the tracing object in inserted before the on response callback is called.
+                span = initialize_span(request, response.error.connection.init_time)
+
+              end
+
+              finish(response, span)
+            end
           end
 
-          def call
-            @request.on(:response, &method(:finish)) # rubocop:disable Performance/MethodObjectAsBlock
+          def finish(response, span)
+            if response.is_a?(::HTTPX::ErrorResponse)
+              span.record_exception(response.error)
+              span.status = Trace::Status.error(response.error.to_s)
+            else
+              span.set_attribute(OpenTelemetry::SemanticConventions::Trace::HTTP_STATUS_CODE, response.status)
+
+              if response.status.between?(400, 599)
+                err = ::HTTPX::HTTPError.new(response)
+                span.record_exception(err)
+                span.status = Trace::Status.error(err.to_s)
+              end
+            end
 
-            uri = @request.uri
-            request_method = @request.verb
-            span_name = "HTTP #{request_method}"
+            span.finish
+          end
+
+          # return a span initialized with the +@request+ state.
+          def initialize_span(request, start_time = ::Time.now)
+            verb = request.verb
+            uri = request.uri
+
+            config = HTTPX::Instrumentation.instance.config
 
             attributes = {
               OpenTelemetry::SemanticConventions::Trace::HTTP_HOST => uri.host,
-              OpenTelemetry::SemanticConventions::Trace::HTTP_METHOD => request_method,
+              OpenTelemetry::SemanticConventions::Trace::HTTP_METHOD => verb,
               OpenTelemetry::SemanticConventions::Trace::HTTP_SCHEME => uri.scheme,
               OpenTelemetry::SemanticConventions::Trace::HTTP_TARGET => uri.path,
               OpenTelemetry::SemanticConventions::Trace::HTTP_URL => "#{uri.scheme}://#{uri.host}",
               OpenTelemetry::SemanticConventions::Trace::NET_PEER_NAME => uri.host,
               OpenTelemetry::SemanticConventions::Trace::NET_PEER_PORT => uri.port
             }
-            config = HTTPX::Instrumentation.instance.config
-            attributes[OpenTelemetry::SemanticConventions::Trace::PEER_SERVICE] = config[:peer_service] if config[:peer_service]
-            attributes.merge!(
-              OpenTelemetry::Common::HTTP::ClientContext.attributes
-            )
 
-            @span = tracer.start_span(span_name, attributes: attributes, kind: :client)
-            trace_ctx = OpenTelemetry::Trace.context_with_span(@span)
-            @trace_token = OpenTelemetry::Context.attach(trace_ctx)
-
-            OpenTelemetry.propagation.inject(@request.headers)
-          rescue StandardError => e
-            OpenTelemetry.handle_error(exception: e)
-          end
+            attributes[OpenTelemetry::SemanticConventions::Trace::PEER_SERVICE] = config[:peer_service] if config[:peer_service]
+            attributes.merge!(OpenTelemetry::Common::HTTP::ClientContext.attributes)
 
-          def finish(response)
-            return unless @span
+            span = tracer.start_span("HTTP #{verb}", attributes: attributes, kind: :client, start_timestamp: start_time)
 
-            if response.is_a?(::HTTPX::ErrorResponse)
-              @span.record_exception(response.error)
-              @span.status = Trace::Status.error("Unhandled exception of type: #{response.error.class}")
-            else
-              @span.set_attribute(OpenTelemetry::SemanticConventions::Trace::HTTP_STATUS_CODE, response.status)
-              @span.status = Trace::Status.error unless HTTP_STATUS_SUCCESS_RANGE.cover?(response.status)
+            OpenTelemetry::Trace.with_span(span) do
+              OpenTelemetry.propagation.inject(request.headers)
             end
 
-            OpenTelemetry::Context.detach(@trace_token) if @trace_token
-            @span.finish
+            span
+          rescue StandardError => e
+            OpenTelemetry.handle_error(exception: e)
           end
 
-          private
-
           def tracer
             HTTPX::Instrumentation.instance.tracer
           end
         end
 
-        # HTTPX::Request overrides
+        # Request patch to initiate the trace on initialization.
         module RequestMethods
-          def __otel_enable_trace!
-            return if @__otel_enable_trace
+          def initialize(*)
+            super
 
-            RequestTracer.new(self).call
-            @__otel_enable_trace = true
+            RequestTracer.call(self)
           end
         end
 
-        # HTTPX::Connection overrides
+        # Connection patch to start monitoring on initialization.
         module ConnectionMethods
-          def send(request)
-            request.__otel_enable_trace!
+          attr_reader :init_time
 
+          def initialize(*)
             super
+
+            @init_time = ::Time.now
           end
         end
       end

instrumentation/httpx/test/instrumentation/plugin_test.rb

@@ -82,7 +82,7 @@
         OpenTelemetry::Trace::Status::ERROR
       )
       _(span.status.description).must_equal(
-        'Unhandled exception of type: HTTPX::TimeoutError'
+        'Timed out'
       )
       assert_requested(
         :get,