flagbearer for C++

The C++ SDK for Flagbearer. Requires C++17, CMake 3.16 or later, and libcurl 7.68 or later, which macOS and most Linux distributions already include.

Install

Add it to your CMake build:

include(FetchContent)
FetchContent_Declare(flagbearer
  GIT_REPOSITORY https://github.com/flagbearer-dev/sdks.git
  GIT_TAG cpp-v0.1.0
  SOURCE_SUBDIR cpp)
FetchContent_MakeAvailable(flagbearer)

target_link_libraries(your_app PRIVATE flagbearer::flagbearer)

An installed copy works with find_package(flagbearer 0.1 REQUIRED) too.

#include <flagbearer/flagbearer.hpp>

Keys

Use a server key, which starts with fbs_. Server keys are secret: read them from the environment, such as FLAGBEARER_SERVER_KEY, and never put them in browser code or in the repository. Browsers use client keys, which start with fbc_, through @flagbearer/web.

Sync at startup

Create one client per process, when the app starts, and wait for it to sync before accepting requests:

const char* key = std::getenv("FLAGBEARER_SERVER_KEY");
if (!key) throw std::runtime_error("Set FLAGBEARER_SERVER_KEY");
auto flags = flagbearer::Client::create(key);

try {
  flags->sync(std::chrono::seconds(10));
} catch (const flagbearer::Error& error) {
  // Keep starting: checks use their defaults, and the SDK retries in the background.
  std::fprintf(stderr, "Initial Flagbearer sync failed: %s\n", error.what());
}

Check per request

Pass each request's user explicitly, and a default:

flagbearer::User user{request.user_id(), request.user_email()};
bool advanced = flags->is_enabled("advanced-search", user, false);

User holds a key and an optional email. Include the email to turn flags on for testers by email. The default is used until the client has synced, and when the flag doesn't exist.

Shut down

Keep the client for the life of the process, not per request. Close it on shutdown. Destroying the client closes it too:

flags->close();

Short-lived processes should call flags->flush() before exiting.