bef278e0d2
Samples that did not compile or run as shown: - res.user_data.get<T>() inside a generic lambda needs the `template` keyword; use explicit parameter types (tour 09, cookbook s15). - listen() on a Unix domain socket fails with port 0 (tour 09, s22). - "*.dev.local" is not a NO_PROXY pattern (c16). - ssl_backend_error() holds a verify result, not an ERR_get_error() value, after a verification failure; decode each with the matching OpenSSL function (c18). - The content provider's `length` is everything that remains, so the sample read the whole file in one call (s05). Statements corrected: - Client keep-alive is off by default; c14 is rewritten around set_keep_alive(true). - Mounted files are looked up before GET handlers (tour 04, s04). - Params keep insertion order, and to_string(Error::Connection) reads "Could not establish connection" (tour 02). - A chunked provider ends with sink.done(), and post_routing_handler runs before the response is sent (tour 09). - Timeouts surface as Error::Read; Error::Timeout comes from the stream API (c17). The max timeout cuts off the wait for the response only (c13). The progress callback needs Content-Length (c11). - Encoding selection follows q-values, then Brotli, gzip, Zstd (s08), and the client compresses with the first of those it was built with (c15). - stop() cuts a provider-driven response short (s19); a rejected content_reader already gets 400 or 413 (s07); user_data values must be copyable (s12); Client accepts a client certificate too (t04); on_message() is the fallback for every unhandled event and 204/403/404 end reconnection (e04); the pong timeout takes two to three intervals and ends a waiting read() (w02). In the LLM app tutorial, an uncaught exception does not crash the server, so say what it does instead. Drop the server and client timeout settings whose stated purpose, covering inference and download time, they do not serve: those timeouts bound a single socket wait. Update the llama.cpp server layout in chapter 7.
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title, order, status
| title | order | status |
|---|---|---|
| S22. Talk Over a Unix Domain Socket | 41 | draft |
When you want to talk only to other processes on the same host, a Unix domain socket is a nice fit. It avoids TCP overhead and uses filesystem permissions for access control. Local IPC and services sitting behind a reverse proxy are classic use cases.
Server side
httplib::Server svr;
svr.set_address_family(AF_UNIX);
svr.Get("/", [](const auto &, auto &res) {
res.set_content("hello from unix socket", "text/plain");
});
svr.listen("/tmp/httplib.sock", 80);
Call set_address_family(AF_UNIX) first, then pass the socket file path as the first argument to listen(). The port number is unused but required by the signature. Pass any value other than 0, which makes listen() fail.
Client side
httplib::Client cli("/tmp/httplib.sock");
cli.set_address_family(AF_UNIX);
auto res = cli.Get("/");
if (res) {
std::cout << res->body << std::endl;
}
Pass the socket file path to the Client constructor and call set_address_family(AF_UNIX). Everything else works like a normal HTTP request.
When to use it
- Behind a reverse proxy: An nginx-to-backend setup over a Unix socket is faster than TCP and sidesteps port management
- Local-only APIs: IPC between tools that shouldn't be reachable from outside
- In-container IPC: Process-to-process communication within the same pod or container
- Dev environments: No more worrying about port conflicts
Clean up the socket file
A Unix domain socket creates a real file in the filesystem. It doesn't get removed on shutdown, so delete it before starting if needed.
std::remove("/tmp/httplib.sock");
svr.listen("/tmp/httplib.sock", 80);
Permissions
You control who can connect via the socket file's permissions.
svr.listen("/tmp/httplib.sock", 80);
// from another process or thread
chmod("/tmp/httplib.sock", 0660); // owner and group only
Warning: Some Windows versions support AF_UNIX, but the implementation and behavior differ by platform. Test thoroughly before running cross-platform in production.