Add Cookbook S01-S22 (draft)

docs-src/pages/en/cookbook/s05-stream-response.md

@@ -0,0 +1,63 @@
+---
+title: "S05. Stream a Large File in the Response"
+order: 24
+status: "draft"
+---
+
+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.
+
+## When the size is known
+
+```cpp
+svr.Get("/download", [](const httplib::Request &req, httplib::Response &res) {
+  size_t total_size = get_file_size("large.bin");
+
+  res.set_content_provider(
+    total_size, "application/octet-stream",
+    [](size_t offset, size_t length, httplib::DataSink &sink) {
+      auto data = read_range_from_file("large.bin", offset, length);
+      sink.write(data.data(), data.size());
+      return true;
+    });
+});
+```
+
+The lambda is called repeatedly with `offset` and `length`. Read just that range and write it to `sink`. Only a small chunk sits in memory at any given time.
+
+## Just send a file
+
+If you only want to serve a file, `set_file_content()` is far simpler.
+
+```cpp
+svr.Get("/download", [](const httplib::Request &req, httplib::Response &res) {
+  res.set_file_content("large.bin", "application/octet-stream");
+});
+```
+
+It streams internally, so even huge files are safe. Omit the Content-Type and it's guessed from the extension.
+
+## When the size is unknown — chunked transfer
+
+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.
+
+```cpp
+svr.Get("/events", [](const httplib::Request &req, httplib::Response &res) {
+  res.set_chunked_content_provider(
+    "text/plain",
+    [](size_t offset, httplib::DataSink &sink) {
+      auto chunk = produce_next_chunk();
+      if (chunk.empty()) {
+        sink.done(); // done sending
+        return true;
+      }
+      sink.write(chunk.data(), chunk.size());
+      return true;
+    });
+});
+```
+
+Call `sink.done()` to signal the end.
+
+> **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.
+
+> To serve the file as a download, see S06. Return a File Download Response.