Add Cookbook C01-C19 (draft)

docs-src/pages/en/cookbook/c14-keep-alive.md

@@ -0,0 +1,53 @@
+---
+title: "C14. Understand Connection Reuse and Keep-Alive"
+order: 14
+status: "draft"
+---
+
+When you send multiple requests through the same `httplib::Client` instance, the TCP connection is reused automatically. HTTP/1.1 Keep-Alive does the work for you — you don't pay the TCP and TLS handshake cost on every call.
+
+## Connections are reused automatically
+
+```cpp
+httplib::Client cli("https://api.example.com");
+
+auto res1 = cli.Get("/users/1");
+auto res2 = cli.Get("/users/2"); // reuses the same connection
+auto res3 = cli.Get("/users/3"); // reuses the same connection
+```
+
+No special config required. Just hold on to `cli` — internally, the socket stays open across calls. The effect is especially noticeable over HTTPS, where the TLS handshake is expensive.
+
+## Disable Keep-Alive explicitly
+
+To force a fresh connection every time, call `set_keep_alive(false)`. Mostly useful for testing.
+
+```cpp
+cli.set_keep_alive(false);
+```
+
+For normal use, leave it on (the default).
+
+## Don't create a `Client` per request
+
+If you create a `Client` inside a loop and let it fall out of scope each iteration, you lose the reuse benefit. Create the instance outside the loop.
+
+```cpp
+// Bad: a new connection every iteration
+for (auto id : ids) {
+  httplib::Client cli("https://api.example.com");
+  cli.Get("/users/" + id);
+}
+
+// Good: the connection is reused
+httplib::Client cli("https://api.example.com");
+for (auto id : ids) {
+  cli.Get("/users/" + id);
+}
+```
+
+## Concurrent requests
+
+If you want to send requests in parallel from multiple threads, give each thread its own `Client` instance. A single `Client` uses a single TCP connection, so firing concurrent requests at the same instance ends up serializing them anyway.
+
+> **Note:** If the server closes the connection after its Keep-Alive timeout, cpp-httplib reconnects and retries transparently. You don't need to handle this in application code.