feat: Add tracing hook. (#496)

Adds support for an OTEL tracing hook.

Unlike other packages we will not be providing a build of this package.
A customer wanting to use this package will need to build the SDK
themselves in the correct configuration. This allows for the hook to use
the version of OpenTelemetry that they are using with their application.


<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Introduces a new server-side OpenTelemetry integration
(`libs/server-sdk-otel`) with a tracing hook, example app, build flags,
CI workflow, and release config.
> 
> - **Server OTEL Integration**:
> - New package `libs/server-sdk-otel` implementing `TracingHook` with
options (`TracingHookOptions`, builder), headers, implementation, unit
tests, `CMakeLists.txt`, `CHANGELOG.md`, and `README.md`.
>   - Exposes target alias `launchdarkly::server_otel`.
> - **Example**:
> - Adds `examples/hello-cpp-server-otel` (CMake, README, main)
demonstrating OTLP HTTP tracing and hook usage.
> - **Build/Config**:
> - Top-level: new options `LD_BUILD_OTEL_SUPPORT`,
`LD_BUILD_OTEL_FETCH_DEPS`, `LD_OTEL_CPP_VERSION`; conditionally
`add_subdirectory(libs/server-sdk-otel)` and example; docs updated in
`README.md`.
> - `libs/server-sdk-otel/CMakeLists.txt`: optional FetchContent of
OpenTelemetry (when `LD_BUILD_OTEL_FETCH_DEPS=ON`), link to
`opentelemetry-cpp::api`.
> - `scripts/build.sh`: auto-enables OTEL flags for
`launchdarkly-cpp-server-otel` and test targets.
>   - `cmake/json.cmake`: rename FetchContent target to `nlohmann_json`.
> - **CI/Release**:
> - New workflow `.github/workflows/server-otel.yml`
(Ubuntu/macOS/Windows) building `launchdarkly-cpp-server-otel` with CURL
dev libs.
> - Composite action `.github/actions/ci`: adds `install_curl` input and
broadens CURL install condition; passes `CMAKE_PREFIX_PATH`.
> - `release-please` config/manifests updated to include
`libs/server-sdk-otel` (initial version `0.1.0`).
>   - Manual docs workflow: adds `libs/server-sdk-otel` option.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
0771956. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: kinyoklion

.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
+)