Ensure the _dd.p.tid tag has fixed size

lib/datadog/tracing/distributed/datadog.rb

@@ -109,7 +109,7 @@ def build_tags(digest)
 
           return tags if high_order == 0
 
-          tags.merge(Tracing::Metadata::Ext::Distributed::TAG_TID => high_order.to_s(16))
+          tags.merge(Tracing::Metadata::Ext::Distributed::TAG_TID => format('%016x', high_order))
         end
 
         # Side effect: Remove high order 64 bit hex-encoded `tid` tag from distributed tags

lib/datadog/tracing/trace_segment.rb

@@ -132,10 +132,13 @@ def sampled?
           || sampling_priority == Sampling::Ext::Priority::USER_KEEP
       end
 
+      # Returns the high order part of the trace id as a hexadecimal string; the most significant 64 bits.
+      # The String returned is padded with zeros, having a fixed length of 16 characters.
+      # If the high order part is zero, it returns nil.
       def high_order_tid
         high_order = Tracing::Utils::TraceId.to_high_order(@id)
 
-        high_order.to_s(16) if high_order != 0
+        format('%016x', high_order) if high_order != 0
       end
 
       protected

spec/datadog/tracing/distributed/datadog_spec.rb

@@ -209,7 +209,7 @@
       context 'when given a trace digest with 128 bit trace id' do
         let(:digest) do
           Datadog::Tracing::TraceDigest.new(
-            trace_id: 0xaaaaaaaaaaaaaaaaffffffffffffffff,
+            trace_id: 0x0aaaaaaaaaaaaaaaffffffffffffffff,
             span_id: 0xbbbbbbbbbbbbbbbb
           )
         end
@@ -220,7 +220,7 @@
           expect(data).to eq(
             'x-datadog-trace-id' => 0xffffffffffffffff.to_s,
             'x-datadog-parent-id' => 0xbbbbbbbbbbbbbbbb.to_s,
-            'x-datadog-tags' => '_dd.p.tid=aaaaaaaaaaaaaaaa'
+            'x-datadog-tags' => '_dd.p.tid=0aaaaaaaaaaaaaaa'
           )
         end
       end
@@ -482,11 +482,11 @@
         {
           prepare_key['x-datadog-trace-id'] => 0xffffffffffffffff.to_s,
           prepare_key['x-datadog-parent-id'] => 0xbbbbbbbbbbbbbbbb.to_s,
-          prepare_key['x-datadog-tags'] => '_dd.p.tid=aaaaaaaaaaaaaaaa'
+          prepare_key['x-datadog-tags'] => '_dd.p.tid=0aaaaaaaaaaaaaaa'
         }
       end
 
-      it { expect(digest.trace_id).to eq(0xaaaaaaaaaaaaaaaaffffffffffffffff) }
+      it { expect(digest.trace_id).to eq(0x0aaaaaaaaaaaaaaaffffffffffffffff) }
       it { expect(digest.span_id).to eq(0xbbbbbbbbbbbbbbbb) }
       it { expect(digest.trace_distributed_tags).not_to include('_dd.p.tid') }
     end

spec/datadog/tracing/trace_segment_spec.rb

@@ -361,10 +361,10 @@
     end
 
     context 'when given 128 bits id' do
-      let(:trace_id) { 0xaaaaaaaaaaaaaaaaffffffffffffffff }
+      let(:trace_id) { 0x0aaaaaaaaaaaaaaaffffffffffffffff }
 
-      it do
-        expect(trace_segment.high_order_tid).to eq('aaaaaaaaaaaaaaaa')
+      it 'returns a fixed-size, 16-char hex string' do
+        expect(trace_segment.high_order_tid).to eq('0aaaaaaaaaaaaaaa')
       end
     end
   end

spec/datadog/tracing/transport/trace_formatter_spec.rb

@@ -13,7 +13,7 @@
 RSpec.describe Datadog::Tracing::Transport::TraceFormatter do
   subject(:trace_formatter) { described_class.new(trace) }
   let(:trace_options) { { id: trace_id } }
-  let(:trace_id) { Datadog::Tracing::Utils::TraceId.next_id }
+  let(:trace_id) { 0xa3efc9f3333333334d39dacf84ab3fe }
 
   shared_context 'trace metadata' do
     let(:trace_tags) do
@@ -199,7 +199,7 @@
               {
                 'foo' => 'bar',
                 '_dd.p.dm' => '-1',
-                '_dd.p.tid' => high_order_hex_trace_id(trace_id),
+                '_dd.p.tid' => '0a3efc9f33333333',
               }
             )
           end

spec/support/tracer_helpers.rb

@@ -121,6 +121,6 @@ def low_order_trace_id(trace_id)
   # Wraps call to Tracing::Utils::TraceId.to_high_order and converts to hex
   # for better test readability
   def high_order_hex_trace_id(trace_id)
-    Datadog::Tracing::Utils::TraceId.to_high_order(trace_id).to_s(16)
+    format('%016x', Datadog::Tracing::Utils::TraceId.to_high_order(trace_id))
   end
 end