feat: Add tracing hook.

.github/actions/ci/action.yml

@@ -33,6 +33,10 @@ inputs:
     description: 'Whether to enable CURL networking (LD_CURL_NETWORKING=ON)'
     required: false
     default: 'false'
+  install_curl:
+    description: 'Whether to install CURL development libraries. Required for OpenTelemetry builds (server-sdk-otel), but does not enable CURL networking for the SDK itself.'
+    required: false
+    default: 'false'
 
 runs:
   using: composite
@@ -49,7 +53,7 @@ runs:
       uses: ./.github/actions/install-openssl
       id: install-openssl
     - name: Install CURL
-      if: inputs.use_curl == 'true'
+      if: inputs.use_curl == 'true' || inputs.install_curl == 'true'
       uses: ./.github/actions/install-curl
       id: install-curl
     - name: Build Library

.github/workflows/manual-publish-doc.yml

@@ -10,6 +10,7 @@ on:
           - libs/client-sdk
           - libs/server-sdk
           - libs/server-sdk-redis-source
+          - libs/server-sdk-otel
 name: Publish Documentation
 jobs:
   build-publish:

.github/workflows/release-please.yml

@@ -14,6 +14,8 @@ jobs:
       package-server-tag: ${{ steps.release.outputs['libs/server-sdk--tag_name'] }}
       package-server-redis-released: ${{ steps.release.outputs['libs/server-sdk-redis-source--release_created'] }}
       package-server-redis-tag: ${{ steps.release.outputs['libs/server-sdk-redis-source--tag_name'] }}
+      package-server-otel-released: ${{ steps.release.outputs['libs/server-sdk-otel--release_created'] }}
+      package-server-otel-tag: ${{ steps.release.outputs['libs/server-sdk-otel--tag_name'] }}
     steps:
       - uses: googleapis/release-please-action@v4
         id: release
@@ -142,3 +144,4 @@ jobs:
       upload-assets: true
       upload-tag-name: ${{ needs.release-please.outputs.package-server-redis-tag }}
       provenance-name: ${{ format('{0}-server-redis-multiple-provenance.intoto.jsonl', matrix.os) }}
+

.github/workflows/server-otel.yml

@@ -0,0 +1,54 @@
+name: libs/server-sdk-otel
+
+on:
+  push:
+    branches: [ main ]
+    paths-ignore:
+      - '**.md' # Do not need to run CI for markdown changes.
+  pull_request:
+    branches: [ "main", "feat/**" ]
+    paths-ignore:
+      - '**.md'
+  schedule:
+    # Run daily at midnight PST
+    - cron: '0 8 * * *'
+
+jobs:
+  build-test-otel:
+    runs-on: ubuntu-22.04
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ./.github/actions/ci
+        with:
+          cmake_target: launchdarkly-cpp-server-otel
+          install_curl: true
+          # We don't produce release artifacts.
+          simulate_release: false
+  build-otel-mac:
+    runs-on: macos-13
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ./.github/actions/ci
+        with:
+          cmake_target: launchdarkly-cpp-server-otel
+          platform_version: 12
+          install_curl: true
+          # We don't produce release artifacts.
+          simulate_release: false
+  build-test-otel-windows:
+    runs-on: windows-2022
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ilammy/msvc-dev-cmd@v1
+      - uses: ./.github/actions/ci
+        env:
+          BOOST_LIBRARY_DIR: 'C:\local\boost_1_87_0\lib64-msvc-14.3'
+          BOOST_LIBRARYDIR: 'C:\local\boost_1_87_0\lib64-msvc-14.3'
+          Boost_DIR: 'C:\local\boost_1_87_0\lib64-msvc-14.3\cmake\Boost-1.87.0'
+        with:
+          cmake_target: launchdarkly-cpp-server-otel
+          platform_version: 2022
+          toolset: msvc
+          install_curl: true
+          # We don't produce release artifacts.
+          simulate_windows_release: false

.release-please-manifest.json

@@ -5,5 +5,6 @@
   "libs/internal": "0.12.1",
   "libs/server-sdk": "3.9.1",
   "libs/server-sdk-redis-source": "2.2.0",
+  "libs/server-sdk-otel": "0.0.0",
   "libs/networking": "0.1.0"
 }

CMakeLists.txt

@@ -108,6 +108,8 @@ option(LD_BUILD_EXAMPLES "Build hello-world examples." ON)
 
 option(LD_BUILD_REDIS_SUPPORT "Build redis support." OFF)
 
+option(LD_BUILD_OTEL_SUPPORT "Build OpenTelemetry integration." OFF)
+
 option(LD_CURL_NETWORKING "Enable CURL-based networking for SSE client (alternative to Boost.Beast/Foxy)" OFF)
 
 # If using 'make' as the build system, CMake causes the 'install' target to have a dependency on 'all', meaning
@@ -220,6 +222,11 @@ if (LD_BUILD_REDIS_SUPPORT)
     add_subdirectory(libs/server-sdk-redis-source)
 endif ()
 
+if (LD_BUILD_OTEL_SUPPORT)
+    message("LaunchDarkly: building OpenTelemetry integration")
+    add_subdirectory(libs/server-sdk-otel)
+endif ()
+
 # Built as static or shared depending on LD_BUILD_SHARED_LIBS variable.
 # This target "links" in common, internal, and sse as object libraries.
 add_subdirectory(libs/client-sdk)

README.md

@@ -66,6 +66,9 @@ Various CMake options are available to customize the client/server SDK builds.
 | `LD_DYNAMIC_LINK_OPENSSL`     | Whether OpenSSL is dynamically linked or not.                                                                                                                                                                                                                            | Off  (static link)                                     | N/A                                       |
 | `LD_BUILD_REDIS_SUPPORT`      | Whether the server-side Redis Source is built or not.                                                                                                                                                                                                                    | Off                                                    | N/A                                       |
 | `LD_CURL_NETWORKING`          | Enable CURL-based networking for all HTTP requests (SSE streams and event delivery). When OFF, Boost.Beast/Foxy is used instead. CURL must be available as a dependency when this option is ON.                                                                          | Off                                                    | N/A                                       |
+| `LD_BUILD_OTEL_SUPPORT`       | Whether the server-side OpenTelemetry integration package is built or not.                                                                                                                                                                                                | Off                                                    | N/A                                       |
+| `LD_BUILD_OTEL_FETCH_DEPS`    | When building OpenTelemetry support, automatically fetch and configure OpenTelemetry dependencies via CMake FetchContent. This is useful for local development and CI. When OFF, you must provide OpenTelemetry yourself via `find_package`.                              | Off                                                    | `LD_BUILD_OTEL_SUPPORT`                   |
+| `LD_OTEL_CPP_VERSION`         | Specifies the OpenTelemetry C++ SDK version (git tag or commit hash) to fetch when `LD_BUILD_OTEL_FETCH_DEPS` is enabled. Can be set to any valid git reference from the [opentelemetry-cpp repository](https://github.com/open-telemetry/opentelemetry-cpp).            | `ea1f0d61ce5baa5584b097266bf133d1f31e3607` (v1.23.0)  | `LD_BUILD_OTEL_FETCH_DEPS`                |
 
 > [!WARNING]   
 > When building shared libraries C++ symbols are not exported, only the C API will be exported. This is because C++ does

cmake/json.cmake

@@ -9,8 +9,9 @@ if (${CMAKE_VERSION} VERSION_GREATER_EQUAL "3.24")
     cmake_policy(SET CMP0135 NEW)
 endif ()
 
-FetchContent_Declare(json
+# Use the same FetchContent name as OpenTelemetry to avoid duplicate targets
+FetchContent_Declare(nlohmann_json
         URL https://github.com/nlohmann/json/releases/download/v3.11.3/json.tar.xz
 )
 
-FetchContent_MakeAvailable(json)
+FetchContent_MakeAvailable(nlohmann_json)

examples/CMakeLists.txt

@@ -8,3 +8,7 @@ if (LD_BUILD_REDIS_SUPPORT)
     add_subdirectory(hello-cpp-server-redis)
     add_subdirectory(hello-c-server-redis)
 endif ()
+
+if (LD_BUILD_OTEL_SUPPORT)
+    add_subdirectory(hello-cpp-server-otel)
+endif ()

examples/hello-cpp-server-otel/CMakeLists.txt

@@ -0,0 +1,23 @@
+# Required for Apple Silicon support.
+cmake_minimum_required(VERSION 3.19)
+
+project(
+        LaunchDarklyHelloCPPServerOTel
+        VERSION 0.1
+        DESCRIPTION "LaunchDarkly Hello CPP Server-side SDK with OpenTelemetry Integration"
+        LANGUAGES CXX
+)
+
+set(THREADS_PREFER_PTHREAD_FLAG ON)
+find_package(Threads REQUIRED)
+
+add_executable(hello-cpp-server-otel main.cpp)
+
+target_link_libraries(hello-cpp-server-otel
+    PRIVATE
+    launchdarkly::server
+    launchdarkly::server_otel
+    Threads::Threads
+    opentelemetry_trace
+    opentelemetry_exporter_otlp_http
+)

examples/hello-cpp-server-otel/README.md

@@ -0,0 +1,85 @@
+# LaunchDarkly C++ Server SDK - OpenTelemetry Integration Example
+
+This example demonstrates how to integrate the LaunchDarkly C++ Server SDK with OpenTelemetry tracing to automatically enrich your distributed traces with feature flag evaluation data.
+
+## What This Example Shows
+
+- Setting up OpenTelemetry with OTLP HTTP exporter
+- Configuring the LaunchDarkly OpenTelemetry tracing hook
+- Creating HTTP spans with Boost.Beast
+- Automatic feature flag span events in traces
+- Passing explicit parent span context to evaluations
+
+## Prerequisites
+
+- C++17 or later
+- CMake 3.19 or later
+- Boost 1.81 or later
+- LaunchDarkly SDK key
+
+## Building
+
+From the repository root:
+
+```bash
+mkdir build && cd build
+cmake .. -DLD_BUILD_EXAMPLES=ON -DLD_BUILD_OTEL_SUPPORT=ON
+cmake --build . --target hello-cpp-server-otel
+```
+
+## Running
+
+### 1. Set Your LaunchDarkly SDK Key
+
+Either edit `main.cpp` and set the `SDK_KEY` constant, or use an environment variable:
+
+```bash
+export LD_SDK_KEY=your-sdk-key-here
+```
+
+### 2. Create a Feature Flag
+
+In your LaunchDarkly dashboard, create a boolean flag named `show-detailed-weather`.
+
+### 3. Run the Example
+
+```bash
+./build/examples/hello-cpp-server-otel/hello-cpp-server-otel
+```
+
+You should see:
+
+```
+*** SDK successfully initialized!
+
+*** Weather server running on http://0.0.0.0:8080
+*** Try: curl http://localhost:8080/weather
+*** OpenTelemetry tracing enabled, sending traces to LaunchDarkly
+*** LaunchDarkly integration enabled with OpenTelemetry tracing hook
+```
+
+### 4. Make Requests
+
+```bash
+curl http://localhost:8080/weather
+```
+
+### 5. View Traces in LaunchDarkly
+
+Navigate to your LaunchDarkly project's Observability section to view traces. Each HTTP request will have:
+1. **Root Span**: "HTTP GET /weather" with HTTP attributes
+2. **Feature Flag Event**: Attached to the span with evaluation details:
+   - `feature_flag.key`: "show-detailed-weather"
+   - `feature_flag.provider.name`: "LaunchDarkly"
+   - `feature_flag.context.id`: "user:weather-api-user"
+   - `feature_flag.result.value`: The evaluated flag value
+
+
+### Custom OTLP Endpoint
+
+To send traces to a different OpenTelemetry collector, set the `LD_OTEL_ENDPOINT` environment variable:
+
+```bash
+export LD_OTEL_ENDPOINT=http://localhost:4318/v1/traces
+./build/examples/hello-cpp-server-otel/hello-cpp-server-otel
+```