GRPCPropagator: handle metadata array values

lib/ddtrace/contrib/grpc/datadog_interceptor/client.rb

@@ -8,7 +8,7 @@ module Contrib
     module GRPC
       module DatadogInterceptor
         # The DatadogInterceptor::Client implements the tracing strategy
-        # for gRPC client-side endpoitns. This middleware compoent will
+        # for gRPC client-side endpoints. This middleware component will
         # inject trace context information into gRPC metadata prior to
         # sending the request to the server.
         class Client < Base

lib/ddtrace/propagation/grpc_propagator.rb

@@ -38,24 +38,32 @@ def valid?
       end
 
       def trace_id
-        value = @metadata[GRPC_METADATA_TRACE_ID].to_i
+        value = metadata_for_key(GRPC_METADATA_TRACE_ID).to_i
         value if (1..Span::EXTERNAL_MAX_ID).cover? value
       end
 
       def parent_id
-        value = @metadata[GRPC_METADATA_PARENT_ID].to_i
+        value = metadata_for_key(GRPC_METADATA_PARENT_ID).to_i
         value if (1..Span::EXTERNAL_MAX_ID).cover? value
       end
 
       def sampling_priority
-        value = @metadata[GRPC_METADATA_SAMPLING_PRIORITY]
+        value = metadata_for_key(GRPC_METADATA_SAMPLING_PRIORITY)
         value && value.to_i
       end
 
       def origin
-        value = @metadata[GRPC_METADATA_ORIGIN]
+        value = metadata_for_key(GRPC_METADATA_ORIGIN)
         value if value != ''
       end
+
+      private
+
+      def metadata_for_key(key)
+        # metadata values can be arrays (multiple headers with the same key)
+        value = @metadata[key]
+        value.is_a?(Array) ? value.first : value
+      end
     end
   end
 end

spec/ddtrace/propagation/grpc_propagator_spec.rb

@@ -85,5 +85,23 @@
         expect(subject.origin).to eq 'synthetics'
       end
     end
+
+    # Metadata values can also be arrays
+    # https://github.com/grpc/grpc-go/blob/master/Documentation/grpc-metadata.md
+    context 'given populated metadata in array format' do
+      let(:metadata) do
+        { 'x-datadog-trace-id' => ['12345', '67890'],
+          'x-datadog-parent-id' => ['98765', '43210'],
+          'x-datadog-sampling-priority' => ['0'],
+          'x-datadog-origin' => ['synthetics'] }
+      end
+
+      it 'returns a populated context with the first metadata array values' do
+        expect(subject.trace_id).to eq 12345
+        expect(subject.span_id).to eq 98765
+        expect(subject.sampling_priority).to be_zero
+        expect(subject.origin).to eq 'synthetics'
+      end
+    end
   end
 end