fix: Fix the array encoding length of datadog version 05 exporter (#1002)

* Fix the array encoding of datadog version 05 exporter

* Fix type for array length

* Fix unit test

* Fix unit test correctly

* opentelemetry-datadog: Add missing Headers

* Version
* Language

* fix: format

---------

Co-authored-by: Harold Dost <[email protected]>
Co-authored-by: Zhongyang Wu <[email protected]>

Author: 3 people

opentelemetry-datadog/src/exporter/mod.rs

@@ -34,6 +34,10 @@ const DEFAULT_AGENT_ENDPOINT: &str = "http://127.0.0.1:8126";
 /// Header name used to inform the Datadog agent of the number of traces in the payload
 const DATADOG_TRACE_COUNT_HEADER: &str = "X-Datadog-Trace-Count";
 
+/// Header name use to inform datadog as to what version
+const DATADOG_META_LANG_HEADER: &str = "Datadog-Meta-Lang";
+const DATADOG_META_TRACER_VERSION_HEADER: &str = "Datadog-Meta-Tracer-Version";
+
 // Struct to hold the mapping between Opentelemetry spans and datadog spans.
 pub struct Mapping {
     resource: Option<FieldMapping>,
@@ -101,6 +105,11 @@ impl DatadogExporter {
             .uri(self.request_url.clone())
             .header(http::header::CONTENT_TYPE, self.api_version.content_type())
             .header(DATADOG_TRACE_COUNT_HEADER, trace_count)
+            .header(DATADOG_META_LANG_HEADER, "rust")
+            .header(
+                DATADOG_META_TRACER_VERSION_HEADER,
+                env!("CARGO_PKG_VERSION"),
+            )
             .body(data)
             .map_err::<Error, _>(Into::into)?;
 

opentelemetry-datadog/src/exporter/model/mod.rs

@@ -282,7 +282,7 @@ pub(crate) mod tests {
 
         assert_eq!(encoded.as_str(), "kp6jd2VirHNlcnZpY2VfbmFtZaljb21wb25lbnSocmVzb3VyY2WpaG9zdC5uYW\
         1lpHRlc3Snc2VydmljZax0ZXN0LXNlcnZpY2WjZW52qHRlc3QtZW52p3ZlcnNpb26sdGVzdC12ZXJzaW9uqXNwYW4udH\
-        lwZbVfc2FtcGxpbmdfcHJpb3JpdHlfdjGRkZ3OAAAAAc4AAAACzgAAAAPPAAAAAAAAAAfPAAAAAAAAAGPPAAAAAAAAAA\
+        lwZbVfc2FtcGxpbmdfcHJpb3JpdHlfdjGRkZzOAAAAAc4AAAACzgAAAAPPAAAAAAAAAAfPAAAAAAAAAGPPAAAAAAAAAA\
         HTAAAAAAAAAADTAAAAADuaygDSAAAAAIXOAAAABM4AAAAFzgAAAAbOAAAAB84AAAAIzgAAAAnOAAAACs4AAAALzgAAAA\
         zOAAAAAIHOAAAADcsAAAAAAAAAAM4AAAAA");
 

opentelemetry-datadog/src/exporter/model/v05.rs

@@ -9,9 +9,11 @@ use std::time::SystemTime;
 
 use super::unified_tags::{UnifiedTagField, UnifiedTags};
 
+const SPAN_NUM_ELEMENTS: u32 = 12;
+
 // Protocol documentation sourced from https://github.com/DataDog/datadog-agent/blob/c076ea9a1ffbde4c76d35343dbc32aecbbf99cb9/pkg/trace/api/version.go
 //
-// The payload is an array containing exactly 2 elements:
+// The payload is an array containing exactly 12 elements:
 //
 // 	1. An array of all unique strings present in the payload (a dictionary referred to by index).
 // 	2. An array of traces, where each trace is an array of spans. A span is encoded as an array having
@@ -154,7 +156,7 @@ where
             };
 
             // Datadog span name is OpenTelemetry component name - see module docs for more information
-            rmp::encode::write_array_len(&mut encoded, 13)?;
+            rmp::encode::write_array_len(&mut encoded, SPAN_NUM_ELEMENTS)?;
             rmp::encode::write_u32(
                 &mut encoded,
                 interner.intern(get_service_name(&span, model_config)),