move extract headers to its own method, this is broken

include/datadog/tracer.h

@@ -18,6 +18,7 @@
 #include "id_generator.h"
 #include "optional.h"
 #include "span.h"
+#include "extraction_util.h"
 #include "tracer_config.h"
 #include "tracer_signature.h"
 
@@ -61,6 +62,9 @@ class Tracer {
   Span create_span();
   Span create_span(const SpanConfig& config);
 
+  // ...
+  Expected<ExtractedData> extract_headers(const DictReader& reader, std::unique_ptr<SpanData> span_data);
+
   // Return a span whose parent and other context is parsed from the specified
   // `reader`, and whose attributes are determined by the optionally specified
   // `config`.  If there is no tracing information in `reader`, then return an
@@ -69,6 +73,9 @@ class Tracer {
   Expected<Span> extract_span(const DictReader& reader);
   Expected<Span> extract_span(const DictReader& reader,
                               const SpanConfig& config);
+  Expected<Span> extract_span(ExtractedData& merged_context,
+                              const SpanConfig& config, 
+                              std::unique_ptr<SpanData> span_data);
 
   // Return a span extracted from the specified `reader` (see `extract_span`).
   // If there is no span to extract, then return a span that is the root of a

src/datadog/tracer.cpp

@@ -16,7 +16,6 @@
 #include "config_manager.h"
 #include "datadog_agent.h"
 #include "extracted_data.h"
-#include "extraction_util.h"
 #include "hex.h"
 #include "json.hpp"
 #include "platform_util.h"
@@ -143,17 +142,9 @@ Span Tracer::create_span(const SpanConfig& config) {
   return span;
 }
 
-Expected<Span> Tracer::extract_span(const DictReader& reader) {
-  return extract_span(reader, SpanConfig{});
-}
-
-Expected<Span> Tracer::extract_span(const DictReader& reader,
-                                    const SpanConfig& config) {
+Expected<ExtractedData> Tracer::extract_headers(const DictReader& reader, std::unique_ptr<SpanData> span_data) {
   assert(!extraction_styles_.empty());
-
   AuditedReader audited_reader{reader};
-
-  auto span_data = std::make_unique<SpanData>();
   Optional<PropagationStyle> first_style_with_trace_id;
   Optional<PropagationStyle> first_style_with_parent_id;
   std::unordered_map<PropagationStyle, ExtractedData> extracted_contexts;
@@ -272,6 +263,26 @@ Expected<Span> Tracer::extract_span(const DictReader& reader,
                                              merged_context.headers_examined));
   }
 
+  return std::move(merged_context);
+}
+
+Expected<Span> Tracer::extract_span(const DictReader& reader) {
+  return extract_span(reader, SpanConfig{});
+}
+
+Expected<Span> Tracer::extract_span(const DictReader& reader,
+                                    const SpanConfig& config) {
+  auto span_data = std::make_unique<SpanData>();
+  auto merged_context = extract_headers(reader, std::move(span_data));
+  if (auto* error = merged_context.if_error()) {
+    return *error;
+  }
+  return extract_span(*merged_context, config, std::move(span_data));
+}
+
+Expected<Span> Tracer::extract_span(ExtractedData& merged_context,
+                                    const SpanConfig& config, 
+                                    std::unique_ptr<SpanData> span_data) {
   // We're done extracting fields.  Now create the span.
   // This is similar to what we do in `create_span`.
   span_data->apply_config(*config_manager_->span_defaults(), config, clock_);