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2.2 KiB
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 auto &req, const auto &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.