---
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, Brotli, or Zstd 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
#define CPPHTTPLIB_ZSTD_SUPPORT    // zstd
#include <httplib.h>
```

You'll also need to link against `zlib`, `brotli`, or `zstd`, whichever you enabled.

## 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 is compressed before sending. The encoding is the first one enabled in your build, in the order Brotli, gzip, Zstd. 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 any compression library, `set_compress(true)` leaves the request uncompressed. And a response compressed with an encoding your build lacks makes the request fail with `Error::UnsupportedContentEncoding`. If compression isn't working, check the macro definitions first.