cpp-httplib/docs-src/pages/en/cookbook/s08-compress-response.md

title, order, status

title	order	status
S08. Return a Compressed Response	27	draft

cpp-httplib automatically compresses response bodies when the client indicates support via Accept-Encoding. The handler doesn't need to do anything special. Supported encodings are gzip, Brotli, and Zstd.

Build-time setup

To enable compression, define the relevant macros before including httplib.h:

#define CPPHTTPLIB_ZLIB_SUPPORT     // gzip
#define CPPHTTPLIB_BROTLI_SUPPORT   // brotli
#define CPPHTTPLIB_ZSTD_SUPPORT     // zstd
#include <httplib.h>

You'll also need to link zlib, brotli, and zstd respectively. Enable only what you need.

Usage

svr.Get("/api/data", [](const httplib::Request &req, httplib::Response &res) {
  std::string body = build_large_response();
  res.set_content(body, "application/json");
});

That's it. If the client sent Accept-Encoding: gzip, cpp-httplib compresses the response with gzip automatically. Content-Encoding: gzip and Vary: Accept-Encoding are added for you.

Encoding priority

When the client accepts multiple encodings, cpp-httplib picks in this order (among those enabled at build time): Brotli → Zstd → gzip. Your code doesn't need to care — you always get the most efficient option available.

Streaming responses are compressed too

Streaming responses via set_chunked_content_provider() get the same automatic compression.

svr.Get("/events", [](const httplib::Request &req, httplib::Response &res) {
  res.set_chunked_content_provider(
    "text/plain",
    [](size_t offset, httplib::DataSink &sink) {
      // ...
    });
});

Note: Tiny responses barely benefit from compression and just waste CPU time. cpp-httplib skips compression for bodies that are too small to bother with.

For the client-side counterpart, see C15. Enable Compression.