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* Add Server::CustomRoute() for HTTP methods outside the built-in set parse_request_line validates the request method against a fixed whitelist and rejects anything else with 400 before routing runs. That blocks WebDAV, where PROPFIND, PROPPATCH, MKCOL, COPY, MOVE, LOCK and UNLOCK are ordinary methods defined by RFC 4918, and it blocks extension methods such as UPnP's SUBSCRIBE. The need has been open since #847. Registering a handler is now what makes the server accept a method: svr.CustomRoute("PROPFIND", "/dav/:id", handler); Because custom methods go through the normal dispatch path, patterns work the way they do for Get() and friends, and the request body is available in req.body. Serving these methods through set_pre_routing_handler was never enough: the body has not been read at that point, so PROPPATCH and LOCK, which require one, could not be implemented at all. A HandlerWithContentReader overload is available too. The content reader gate in routing() also fires when a custom method carries no body, matching what expect_content() does unconditionally for POST/PUT/PATCH/DELETE, so a body-less PROPFIND (RFC 4918 treats one as allprop) reaches its handler instead of falling through to 404. Method names are validated as RFC 9110 tokens, and the ten built-in methods are refused. Seven of them are dispatched by the if/else chain in routing() before the custom tables are consulted, so a route registered for one could never fire; CONNECT, TRACE and PRI carry protocol-level meaning this library does not route. A refused registration makes is_valid() return false, so listen() fails rather than starting a server holding a handler that would never run. This is also why SSLServer::is_valid() now chains to Server::is_valid() instead of only checking ctx_. Servers that never call CustomRoute() keep the previous per-request cost: the built-in method set is checked first and short-circuits, and the custom lookup returns early on an empty map. * Add cookbook recipe for custom HTTP methods The CustomRoute() docs were a section inside S01, which pushed that page to 90 lines, the longest in the cookbook, and mixed a separate feature into a page about registering GET/POST/PUT/DELETE handlers. Move the section into its own recipe and give it room for the part that was missing: the OPTIONS handler returning DAV: and Allow, which WebDAV clients probe for before anything else. S01 goes back to 68 lines and keeps a pointer to the new page. The recipe is titled after the API rather than after WebDAV, and says outright that generating the 207 Multi-Status XML, interpreting Depth and managing locks are the reader's job. Routing the method is all the library does. S23 takes order 42, so the TLS, SSE and WebSocket recipes shift to 43-57. That only moves the sort key. Filenames, the T01/E01/W01 labels, the published URLs and every cross-reference are untouched.
2.9 KiB
title, order, status
| title | order | status |
|---|---|---|
| E01. Implement an SSE Server | 48 | draft |
Server-Sent Events (SSE) is a simple protocol for pushing events one-way from server to client. The connection stays open, and the server can send data whenever it wants. It's lighter than WebSocket and fits entirely within HTTP — a nice combination.
cpp-httplib doesn't have a dedicated SSE server API, but you can implement one with set_chunked_content_provider() and text/event-stream.
Basic SSE server
svr.Get("/events", [](const httplib::Request &req, httplib::Response &res) {
res.set_chunked_content_provider(
"text/event-stream",
[](size_t offset, httplib::DataSink &sink) {
std::string message = "data: hello\n\n";
sink.write(message.data(), message.size());
std::this_thread::sleep_for(std::chrono::seconds(1));
return true;
});
});
Three things matter here:
- Content-Type is
text/event-stream - Messages follow the format
data: <content>\n\n(the double newline separates events) - Each
sink.write()delivers data to the client
The provider lambda keeps being called as long as the connection is alive.
A continuous stream
Here's a simple example that sends the current time once per second.
svr.Get("/time", [](const httplib::Request &req, httplib::Response &res) {
res.set_chunked_content_provider(
"text/event-stream",
[&req](size_t offset, httplib::DataSink &sink) {
if (req.is_connection_closed()) {
sink.done();
return true;
}
auto now = std::chrono::system_clock::now();
auto t = std::chrono::system_clock::to_time_t(now);
std::string msg = "data: " + std::string(std::ctime(&t)) + "\n";
sink.write(msg.data(), msg.size());
std::this_thread::sleep_for(std::chrono::seconds(1));
return true;
});
});
When the client disconnects, call sink.done() to stop. Details in S16. Detect client disconnection.
Heartbeats via comment lines
Lines starting with : are SSE comments — clients ignore them, but they keep the connection alive. Handy for preventing proxies and load balancers from closing idle connections.
// heartbeat every 30 seconds
if (tick_count % 30 == 0) {
std::string ping = ": ping\n\n";
sink.write(ping.data(), ping.size());
}
Relationship with the thread pool
SSE connections stay open, so each client holds a worker thread. For lots of concurrent connections, enable dynamic scaling on the thread pool.
svr.new_task_queue = [] {
return new httplib::ThreadPool(8, 128);
};
See S21. Configure the thread pool.
Note: When
data:contains newlines, split it into multipledata:lines — one per line. This is how the SSE spec requires multiline data to be transmitted.
For event names, see E02. Use named events in SSE. For the client side, see E04. Receive SSE on the client.