feat: Publish OTel process context

BUILD.bazel

@@ -39,6 +39,10 @@ cc_library(
         "src/datadog/msgpack.cpp",
         "src/datadog/msgpack.h",
         "src/datadog/null_logger.h",
+        "src/datadog/otel_process_ctx.cpp",
+        "src/datadog/otel_process_ctx.h",
+        "src/datadog/otel_process_ctx_registration.cpp",
+        "src/datadog/otel_process_ctx_registration.h",
         "src/datadog/parse_util.cpp",
         "src/datadog/parse_util.h",
         "src/datadog/platform_util.h",

CMakeLists.txt

@@ -197,6 +197,8 @@ target_sources(dd-trace-cpp-objects
     src/datadog/limiter.cpp
     src/datadog/logger.cpp
     src/datadog/msgpack.cpp
+    src/datadog/otel_process_ctx.cpp
+    src/datadog/otel_process_ctx_registration.cpp
     src/datadog/parse_util.cpp
     src/datadog/propagation_behavior_extract.cpp
     src/datadog/propagation_style.cpp

LICENSE-3rdparty.csv

@@ -2,4 +2,5 @@ Component,Origin,License,Copyright
 vendored,nlohmann/json,MIT,Copyright (c) 2013-2022 Niels Lohmann <http://nlohmann.me>
 vendored,Catch2,Boost,Copyright (c) 2022 Two Blue Cubes Ltd. All rights reserved.
 vendored,picosha2,MIT,Copyright (C) 2017 okdshin
-vendored,cpp-httplib,MIT,Copyright (c) 2023 Yuji Hirose. All rights reserved.
+vendored,cpp-httplib,MIT,Copyright (c) 2023 Yuji Hirose. All rights reserved.
+vendored,open-telemetry/sig-profiling (process-context),Apache-2.0,"Copyright 2025 Datadog, Inc."

cmake/deps/msgpack.cmake

@@ -0,0 +1,19 @@
+include(FetchContent)
+
+# Header-only; used only by the test suite to decode msgpack payloads written
+# by the library, so we don't need Boost, its own tests, examples, or docs.
+set(MSGPACK_USE_BOOST OFF CACHE BOOL "" FORCE)
+set(MSGPACK_CXX17 ON CACHE BOOL "" FORCE)
+set(MSGPACK_BUILD_TESTS OFF CACHE BOOL "" FORCE)
+set(MSGPACK_BUILD_EXAMPLES OFF CACHE BOOL "" FORCE)
+set(MSGPACK_BUILD_DOCS OFF CACHE BOOL "" FORCE)
+
+FetchContent_Declare(msgpack-cxx
+  URL https://github.com/msgpack/msgpack-c/archive/refs/tags/cpp-8.0.0.tar.gz
+  URL_HASH SHA256=f634fb7052da4478096f2a02dfb6d91174e5836b317afb006375249ccb086aa8
+  FIND_PACKAGE_ARGS NAMES msgpack-cxx
+  EXCLUDE_FROM_ALL
+  SYSTEM
+)
+
+FetchContent_MakeAvailable(msgpack-cxx)

include/datadog/tracer.h

@@ -34,6 +34,7 @@ class TraceSampler;
 class SpanSampler;
 class IDGenerator;
 class InMemoryFile;
+class OtelCtxRegistration;
 
 class Tracer {
   std::shared_ptr<Logger> logger_;
@@ -53,6 +54,7 @@ class Tracer {
   // read to determine if the process is instrumented with a tracer and to
   // retrieve relevant tracing information.
   std::shared_ptr<InMemoryFile> metadata_file_;
+  std::unique_ptr<OtelCtxRegistration> otel_context_registration_;
   Baggage::Options baggage_opts_;
   bool baggage_injection_enabled_;
   bool baggage_extraction_enabled_;
@@ -67,6 +69,15 @@ class Tracer {
   Tracer(const FinalizedTracerConfig& config,
          const std::shared_ptr<const IDGenerator>& generator);
 
+  ~Tracer();
+
+  // Move-only. OtelCtxRegistration is a per-tracer-instance handle; duplicating
+  // ownership would break that invariant, thus copies are disallowed.
+  Tracer(Tracer&&) noexcept;
+  Tracer& operator=(Tracer&&) noexcept;
+  Tracer(const Tracer&) = delete;
+  Tracer& operator=(const Tracer&) = delete;
+
   // Create a new trace and return the root span of the trace. Optionally
   // specify a `config` indicating the attributes of the root span.
   Span create_span();

include/datadog/version.h

@@ -4,6 +4,9 @@
 
 namespace datadog::tracing {
 
+// This library's name
+extern const char *const tracer_library_name;
+
 // The release version at or before this code revision, e.g. "v0.1.12".
 // That is, this code is at least as recent as `tracer_version`, but may be
 // more recent.

src/datadog/error.cpp

@@ -1,13 +1,14 @@
 #include <datadog/error.h>
+#include <datadog/version.h>
 
 #include <ostream>
 
 namespace datadog {
 namespace tracing {
 
 std::ostream& operator<<(std::ostream& stream, const Error& error) {
-  return stream << "[dd-trace-cpp error code " << int(error.code) << "] "
-                << error.message;
+  return stream << "[" << tracer_library_name << " error code "
+                << int(error.code) << "] " << error.message;
 }
 
 Error Error::with_prefix(StringView prefix) const {