fix: trace id mismatch

Some 128-bit w3c trace IDs in the wild contain a zero-padded
64-bit portion. This commit sets the default high part of the
trace ID to 0, ensuring the check passes correctly.

Resolves #83

Author: dmehala

kong/plugins/ddtrace/datadog_propagation.lua

@@ -56,7 +56,7 @@ local function extract_datadog(get_header, max_header_size)
     end
 
     -- other headers are expected but aren't provided in all cases
-    local trace_id = { high = nil, low = trace_id_low }
+    local trace_id = { high = 0, low = trace_id_low }
     local parent_id = parse_uint64(get_header("x-datadog-parent-id"), 10)
     local sampling_priority = tonumber(get_header("x-datadog-sampling-priority"))
     local origin = get_header("x-datadog-origin")

spec/01-unit-tests/03_propagation_spec.lua

@@ -76,7 +76,7 @@ describe("trace propagation", function()
 
             local span = multi_propagator:extract_or_create_span(request, default_span_opts)
 
-            local expected_trace_id = { high = nil, low = 12345678901234567890ULL }
+            local expected_trace_id = { high = 0, low = 12345678901234567890ULL }
             local expected_parent_id = 9876543210987654321ULL
             assert.same(expected_trace_id, span.trace_id)
             assert.same(expected_parent_id, span.parent_id)

spec/01-unit-tests/06_datadog_propagation_spec.lua

@@ -44,7 +44,7 @@ describe("trace propagation", function()
             assert.is_nil(err)
             assert.is_not_nil(extracted)
 
-            local expected_trace_id = { high = nil, low = 12345678901234567890ULL }
+            local expected_trace_id = { high = 0, low = 12345678901234567890ULL }
             assert.same(expected_trace_id, extracted.trace_id)
             assert.equal(9876543210987654321ULL, extracted.parent_id)
             assert.equal(1, extracted.sampling_priority)