CURLOPT_ACCEPT_ENCODING(3)

📦
version 8.18.0 · 24 versions
, in fedora 44

✨ CURLOPT_ACCEPT_ENCODING(3) ✨

okay so bestie, welcome to the Library Functions Manual page for CURLOPT_ACCEPT_ENCODING — it's literally the “automatic decompression of HTTP downloads” girlie, and she has main character energy. 🦋

💖 NAME 💖

  • CURLOPT_ACCEPT_ENCODING — automatic decompression of HTTP downloads ✨

🦋 SYNOPSIS 🦋

#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_ACCEPT_ENCODING, char *enc);

🎀 DESCRIPTION 🎀

You pass in a char * pointer argument specifying what encoding you would like. This sets the contents of the Accept-Encoding: header sent in an HTTP request, and it enables decoding of a response when a Content-Encoding: header is received. 💅

ngl, libcurl potentially supports several different compressed encodings depending on what support has been built in. To aid applications not having to bother about what specific algorithms this particular libcurl build supports, libcurl allows a zero-length string to be set ("") to ask for an Accept-Encoding: header to be used that contains all built-in supported encodings. ✨

Alternatively, you can specify exactly the encoding or list of encodings you want in the response. The following encodings are supported:

  • identity — meaning non-compressed
  • deflate — which requests the server to compress its response using the zlib algorithm
  • gzip — which requests the gzip algorithm
  • br — (since curl 7.57.0) which is brotli
  • zstd — (since curl 7.72.0) which is zstd

Provide them in the string as a comma-separated list of accepted encodings, like: "br, gzip, deflate". 🎀

Set CURLOPT_ACCEPT_ENCODING(3) to NULL to explicitly disable it, which makes libcurl not send an Accept-Encoding: header and not decompress received contents automatically. 🙈

You can also opt to just include the Accept-Encoding: header in your request with CURLOPT_HTTPHEADER(3) but then there is no automatic decompressing when receiving data. 💀

Setting this option is a request, not an order; the server may or may not do it. It must be set (to any non-NULL value) or else any encoding done by the server is ignored. 👑

Servers might respond with Content-Encoding even without getting an Accept-Encoding: in the request. Servers might respond with a different Content-Encoding than what was asked for in the request. 😭

The Content-Length: header field servers send for a compressed response is supposed to indicate the length of the compressed content so when auto decoding is enabled it may not match the sum of bytes reported by the write callbacks (although, sending the length of the non-compressed content is a common server mistake). 🫶

The application does not have to keep the string around after setting this option. 🌸

Using this option multiple times makes the last set string override the previous ones. ⭐

WARNING: when decompressing data, even tiny transfers might be expanded and generate a huge amount of bytes. 🚨

🌸 HISTORY 🌸

This option was called CURLOPT_ENCODING before 7.21.6. 🕰️

🧚 NOTES 🧚

The specific libcurl you are using must have been built with zlib to be able to decompress gzip and deflate responses, with the brotli library to decompress brotli responses and with the zstd library to decompress zstd responses. 🔥

🎀 DEFAULT 🎀

NULL

🌈 PROTOCOLS 🌈

This functionality affects http only. 💅

⭐ EXAMPLE ⭐

int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");

    /* enable all supported built-in compressions */
    curl_easy_setopt(curl, CURLOPT_ACCEPT_ENCODING, "");

    /* Perform the request */
    curl_easy_perform(curl);
  }
}

💜 AVAILABILITY 💜

Added in curl 7.21.6. ✨

🍓 RETURN VALUE 🍓

curl_easy_setopt(3) returns a CURLcode indicating success or error.

CURLE_OK (0) means everything was OK, non-zero means an error occurred, see libcurl-errors(3). 😭

🦋 SEE ALSO 🦋

xoxo, libcurl — 2026-10-12 — CURLOPT_ACCEPT_ENCODING(3) 💖🫶

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