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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 |
|---|---|---|
| S15. Log Requests on the Server | 34 | draft |
To log the requests the server receives and the responses it returns, use Server::set_logger(). The callback fires once per completed request, making it the foundation for access logs and metrics collection.
Basic usage
svr.set_logger([](const httplib::Request &req, const httplib::Response &res) {
std::cout << req.remote_addr << " "
<< req.method << " " << req.path
<< " -> " << res.status << std::endl;
});
The log callback receives both the Request and the Response. You can grab the method, path, status, client IP, headers, body — whatever you need.
Access-log style format
Here's an Apache/Nginx-ish access log format.
svr.set_logger([](const auto &req, const auto &res) {
auto now = std::time(nullptr);
char timebuf[32];
std::strftime(timebuf, sizeof(timebuf), "%Y-%m-%d %H:%M:%S",
std::localtime(&now));
std::cout << timebuf << " "
<< req.remote_addr << " "
<< "\"" << req.method << " " << req.path << "\" "
<< res.status << " "
<< res.body.size() << "B"
<< std::endl;
});
Measure request time
To include request duration in the log, stash a start timestamp in res.user_data from a pre-routing handler, then subtract in the logger.
svr.set_pre_routing_handler([](const auto &req, auto &res) {
res.user_data.set("start", std::chrono::steady_clock::now());
return httplib::Server::HandlerResponse::Unhandled;
});
svr.set_logger([](const httplib::Request &req, const httplib::Response &res) {
auto *start = res.user_data.get<std::chrono::steady_clock::time_point>("start");
auto elapsed = start
? std::chrono::duration_cast<std::chrono::milliseconds>(
std::chrono::steady_clock::now() - *start).count()
: 0;
std::cout << req.method << " " << req.path
<< " " << res.status << " " << elapsed << "ms" << std::endl;
});
For more on user_data, see S12. Pass data between handlers with res.user_data.
Note: The logger runs synchronously on the same thread as request processing. Heavy work inside it hurts throughput — push it to a queue and process asynchronously if you need anything expensive.