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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.
86 lines
2.8 KiB
Markdown
86 lines
2.8 KiB
Markdown
---
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title: "E03. Handle SSE Reconnection"
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order: 50
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status: "draft"
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---
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SSE connections drop for all sorts of network reasons. Clients automatically try to reconnect, so it's a good idea to make your server resume from where it left off.
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## Read `Last-Event-ID`
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When the client reconnects, it sends the ID of the last event it received in the `Last-Event-ID` header. The server reads that and picks up from the next one.
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```cpp
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svr.Get("/events", [](const httplib::Request &req, httplib::Response &res) {
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auto last_id = req.get_header_value("Last-Event-ID");
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int start = last_id.empty() ? 0 : std::stoi(last_id) + 1;
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res.set_chunked_content_provider(
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"text/event-stream",
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[start](size_t offset, httplib::DataSink &sink) mutable {
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static int next_id = 0;
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if (next_id < start) { next_id = start; }
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std::string msg = "id: " + std::to_string(next_id) + "\n"
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+ "data: event " + std::to_string(next_id) + "\n\n";
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sink.write(msg.data(), msg.size());
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++next_id;
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std::this_thread::sleep_for(std::chrono::seconds(1));
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return true;
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});
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});
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```
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On the first connect, `Last-Event-ID` is empty, so start from `0`. On reconnect, resume from the next ID. Event history is the server's responsibility — you need to keep recent events around somewhere.
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## Set the reconnect interval
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Sending a `retry:` field tells the client how long to wait before reconnecting, in milliseconds.
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```cpp
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std::string msg = "retry: 5000\n\n"; // reconnect after 5 seconds
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sink.write(msg.data(), msg.size());
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```
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Usually you send this once at the start. During peak load or maintenance windows, a longer retry interval helps reduce reconnect storms.
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## Buffer recent events
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To support reconnection, keep a rolling buffer of recent events on the server.
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```cpp
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struct EventBuffer {
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std::mutex mu;
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std::deque<std::pair<int, std::string>> events; // {id, data}
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int next_id = 0;
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void push(const std::string &data) {
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std::lock_guard<std::mutex> lock(mu);
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events.push_back({next_id++, data});
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if (events.size() > 1000) { events.pop_front(); }
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}
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std::vector<std::pair<int, std::string>> since(int id) {
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std::lock_guard<std::mutex> lock(mu);
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std::vector<std::pair<int, std::string>> out;
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for (const auto &e : events) {
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if (e.first >= id) { out.push_back(e); }
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}
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return out;
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}
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};
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```
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When a client reconnects, call `since(last_id)` to send any events it missed.
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## How much to keep
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The buffer size is a tradeoff between memory and how far back a client can resume. It depends on the use case:
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- Real-time chat: a few minutes to half an hour
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- Notifications: the last N items
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- Trading data: persist to a database and pull from there
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> **Warning:** `Last-Event-ID` is a client-provided value — don't trust it blindly. If you read it as a number, validate the range. If it's a string, sanitize it.
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