[receiver/datadog]: Fix #23150 (missing span.Resource) (#23814)

**Description:**
Fixes
#23150
by include the original `dd.span.Resource` in the attributes of the
translated span

**Link to tracking Issue:**
[23150](#23150)

**Testing:** Added test that span.Resource is included in translate
attributes

**Documentation:** Added note on `dd.span.Resource` to datadog receiver
README

Author: hughsimpson

.chloggen/issue-23150.yaml

@@ -0,0 +1,20 @@
+# Use this changelog template to create an entry for release notes.
+# If your change doesn't affect end users, such as a test fix or a tooling change,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: datadogreceiver
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Include datadog span.Resource in translated span attributes
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [23150]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:

receiver/datadogreceiver/README.md

@@ -43,4 +43,6 @@ All config params here are valid as well
 
 https://github.com/open-telemetry/opentelemetry-collector/tree/main/config/confighttp#server-configuration
 
+### Default Attributes
 
+- `dd.span.Resource`: The datadog resource name (as distinct from the span name)

receiver/datadogreceiver/translator.go

@@ -84,6 +84,7 @@ func toTraces(payload *pb.TracerPayload, req *http.Request) ptrace.Traces {
 			newSpan.SetParentSpanID(uInt64ToSpanID(span.ParentID))
 			newSpan.SetName(span.Name)
 			newSpan.Status().SetCode(ptrace.StatusCodeOk)
+			newSpan.Attributes().PutStr("dd.span.Resource", span.Resource)
 
 			if span.Error > 0 {
 				newSpan.Status().SetCode(ptrace.StatusCodeError)

receiver/datadogreceiver/translator_test.go

@@ -74,11 +74,13 @@ func TestTracePayloadV05Unmarshalling(t *testing.T) {
 	assert.Equal(t, 1, translated.SpanCount(), "Span Count wrong")
 	span := translated.ResourceSpans().At(0).ScopeSpans().At(0).Spans().At(0)
 	assert.NotNil(t, span)
-	assert.Equal(t, 4, span.Attributes().Len(), "missing tags")
+	assert.Equal(t, 5, span.Attributes().Len(), "missing tags")
 	value, exists := span.Attributes().Get("service.name")
 	assert.True(t, exists, "service.name missing")
 	assert.Equal(t, "my-service", value.AsString(), "service.name tag value incorrect")
 	assert.Equal(t, "my-name", span.Name())
+	spanResource, _ := span.Attributes().Get("dd.span.Resource")
+	assert.Equal(t, "my-resource", spanResource.Str())
 }
 
 func TestTracePayloadV07Unmarshalling(t *testing.T) {
@@ -106,6 +108,7 @@ func TestTracePayloadV07Unmarshalling(t *testing.T) {
 	assert.True(t, exists, "service.name missing")
 	assert.Equal(t, "my-service", value, "service.name tag value incorrect")
 	assert.Equal(t, "my-name", span.GetName())
+	assert.Equal(t, "my-resource", span.GetResource())
 }
 
 func BenchmarkTranslatorv05(b *testing.B) {