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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.
65 lines
2.2 KiB
Markdown
65 lines
2.2 KiB
Markdown
---
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title: "S05. Stream a Large File in the Response"
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order: 24
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status: "draft"
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---
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When the response is a huge file or data generated on the fly, loading the whole thing into memory isn't realistic. Use `Response::set_content_provider()` to produce data in chunks as you send it.
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## When the size is known
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```cpp
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svr.Get("/download", [](const httplib::Request &req, httplib::Response &res) {
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size_t total_size = get_file_size("large.bin");
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res.set_content_provider(
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total_size, "application/octet-stream",
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[](size_t offset, size_t length, httplib::DataSink &sink) {
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auto n = std::min(length, size_t(64 * 1024));
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auto data = read_range_from_file("large.bin", offset, n);
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sink.write(data.data(), data.size());
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return true;
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});
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});
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```
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The lambda is called repeatedly with `offset`, the position sent so far, and `length`, the number of bytes still to send. Cap how much you read per call and write it to `sink`, and only a small chunk sits in memory at any given time.
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## Just send a file
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If you only want to serve a file, `set_file_content()` is far simpler.
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```cpp
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svr.Get("/download", [](const httplib::Request &req, httplib::Response &res) {
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res.set_file_content("large.bin", "application/octet-stream");
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});
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```
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It streams internally, so even huge files are safe. Omit the Content-Type and it's guessed from the extension.
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## When the size is unknown — chunked transfer
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For data generated on the fly, where you don't know the total size up front, use `set_chunked_content_provider()`. It's sent with HTTP chunked transfer encoding.
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```cpp
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svr.Get("/events", [](const httplib::Request &req, httplib::Response &res) {
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res.set_chunked_content_provider(
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"text/plain",
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[](size_t offset, httplib::DataSink &sink) {
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auto chunk = produce_next_chunk();
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if (chunk.empty()) {
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sink.done(); // done sending
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return true;
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}
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sink.write(chunk.data(), chunk.size());
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return true;
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});
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});
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```
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Call `sink.done()` to signal the end.
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> **Note:** The provider lambda is called multiple times. Watch out for the lifetime of captured variables — wrap them in a `std::shared_ptr` if needed.
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> To serve the file as a download, see [S06. Return a file download response](../s06-download-response).
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