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 |
|---|---|---|
| S12. Pass Data Between Handlers with res.user_data | 31 | draft |
Say your pre-request handler decodes an auth token and you want the route handler to use the result. That "data handoff between handlers" is what res.user_data is for — it holds values of arbitrary types.
Basic usage
struct AuthUser {
std::string id;
std::string name;
bool is_admin;
};
svr.set_pre_request_handler(
[](const httplib::Request &req, httplib::Response &res) {
auto token = req.get_header_value("Authorization");
auto user = decode_token(token); // decode the auth token
res.user_data.set("user", user);
return httplib::Server::HandlerResponse::Unhandled;
});
svr.Get("/me", [](const httplib::Request &req, httplib::Response &res) {
auto *user = res.user_data.get<AuthUser>("user");
if (!user) {
res.status = 401;
return;
}
res.set_content("Hello, " + user->name, "text/plain");
});
user_data.set() stores a value of any type, and user_data.get<T>() retrieves it. If you give the wrong type you get nullptr back — so be careful.
Typical value types
Strings, numbers, structs, std::shared_ptr: anything copyable works.
res.user_data.set("user_id", std::string{"42"});
res.user_data.set("is_admin", true);
res.user_data.set("started_at", std::chrono::steady_clock::now());
Where to set, where to read
The usual flow is: set it in set_pre_routing_handler() or set_pre_request_handler(), read it in the route handler. Pre-request runs after routing, so you can combine it with req.matched_route to set values only for specific routes.
A gotcha
user_data lives on Response, not Request. That's because handlers get Response& (mutable) but only const Request&. It looks odd at first, but it makes sense once you think of it as "the mutable context shared between handlers."
Warning:
user_data.get<T>()returnsnullptrwhen the type doesn't match. Use the exact same type on set and get. Storing asAuthUserand fetching asconst AuthUserwon't work.