boost-asio-pro

# Boost.Asio / standalone Asio ## Overview Write async C++ networking code that compiles on the *user's* Boost, not the newest one. Asio's API changed shape three times (classic `io_service` → `io_context` → C++20 coroutines) and most Asio code on the internet is from the first era, so **pick the style from the toolchain first**, then follow that style's reference file. **References:** [Boost.Asio](https://www.boost.org/doc/libs/latest/doc/html/boost_asio.html) · [standalone Asio](https://think-async.com/Asio/) Use this skill whenever async C++ networking code is being written or reviewed — and especially when the target toolchain is old, where coroutine examples simply will not compile. The three worked implementations it references are CI-verified from Boost 1.62 (2016) through 1.90. ## Step 1: pick the style (do this before writing code) Determine the Boost (or Asio) version and the C++ standard actually in use — `find_package(Boost)` output, `dpkg -l libboost-dev`, `brew info boost`, `CMAKE_CXX_STANDARD`, or ask. Do not assume the newest. | Boost | C++ std | Style | Read | |-------|---------|-------|------| | ≥ 1.77 | C++20 | Coroutines (`co_await` + `awaitable<T>`) — preferred | [references/coroutines.md](references/coroutines.md) | | �� 1.74 | C++11–17 | Completion handlers (callbacks) — the portable baseline | [references/pre-cpp20.md](references/pre-cpp20.md) | | ≥ 1.80 | C++11–17 | Stackful `asio::spawn` + `yield_context` (links Boost.Coroutine — not header-on...