Add Cookbook C01-C19 (draft)

docs-src/pages/en/cookbook/c15-compression.md

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+---
+title: "C15. Enable Compression"
+order: 15
+status: "draft"
+---
+
+cpp-httplib supports compression when sending and decompression when receiving. You just need to build it with zlib or Brotli enabled.
+
+## Build-time setup
+
+To use compression, define these macros before including `httplib.h`:
+
+```cpp
+#define CPPHTTPLIB_ZLIB_SUPPORT    // gzip / deflate
+#define CPPHTTPLIB_BROTLI_SUPPORT  // brotli
+#include <httplib.h>
+```
+
+You'll also need to link against `zlib` or `brotli`.
+
+## Compress the request body
+
+```cpp
+httplib::Client cli("https://api.example.com");
+cli.set_compress(true);
+
+std::string big_payload = build_payload();
+auto res = cli.Post("/api/data", big_payload, "application/json");
+```
+
+With `set_compress(true)`, the body of POST or PUT requests gets gzipped before sending. The server needs to handle compressed bodies too.
+
+## Decompress the response
+
+```cpp
+httplib::Client cli("https://api.example.com");
+cli.set_decompress(true); // on by default
+
+auto res = cli.Get("/api/data");
+std::cout << res->body << std::endl;
+```
+
+With `set_decompress(true)`, the client automatically decompresses responses that arrive with `Content-Encoding: gzip` or similar. `res->body` contains the decompressed data.
+
+It's on by default, so normally you don't need to do anything. Set it to `false` only if you want the raw compressed bytes.
+
+> **Warning:** If you build without `CPPHTTPLIB_ZLIB_SUPPORT`, calling `set_compress()` or `set_decompress()` does nothing. If compression isn't working, check the macro definition first.