Add Cookbook C01-C19 (draft)

docs-src/pages/en/cookbook/c02-json.md

@@ -0,0 +1,36 @@
+---
+title: "C02. Send and Receive JSON"
+order: 2
+status: "draft"
+---
+
+cpp-httplib doesn't include a JSON parser. Use a library like [nlohmann/json](https://github.com/nlohmann/json) to build and parse JSON. The examples here use `nlohmann/json`.
+
+## Send JSON
+
+```cpp
+httplib::Client cli("http://localhost:8080");
+
+nlohmann::json j = {{"name", "Alice"}, {"age", 30}};
+auto res = cli.Post("/api/users", j.dump(), "application/json");
+```
+
+Pass the JSON string as the second argument to `Post()` and the Content-Type as the third. The same pattern works with `Put()` and `Patch()`.
+
+> **Warning:** If you omit the Content-Type (the third argument), the server may not recognize the body as JSON. Always specify `"application/json"`.
+
+## Receive a JSON response
+
+```cpp
+auto res = cli.Get("/api/users/1");
+if (res && res->status == 200) {
+  auto j = nlohmann::json::parse(res->body);
+  std::cout << j["name"] << std::endl;
+}
+```
+
+`res->body` is a `std::string`, so you can pass it straight to your JSON library.
+
+> **Note:** Servers sometimes return HTML on errors. Check the status code before parsing to be safe. Some APIs also require an `Accept: application/json` header. If you're calling a JSON API repeatedly, C03. Set default headers can save you some boilerplate.
+
+> For how to receive and return JSON on the server side, see S02. Receive JSON requests and return JSON responses.