---
c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
SPDX-License-Identifier: curl
Title: CURLOPT_ACCEPT_ENCODING
Section: 3
Source: libcurl
See-also:
  - CURLOPT_HTTPHEADER (3)
  - CURLOPT_HTTP_CONTENT_DECODING (3)
  - CURLOPT_TRANSFER_ENCODING (3)
Protocol:
  - HTTP
Added-in: 7.21.6
---

# NAME

CURLOPT_ACCEPT_ENCODING - automatic decompression of HTTP downloads

# SYNOPSIS

~~~c
#include <curl/curl.h>

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

# DESCRIPTION

Pass a char pointer argument specifying what encoding you would like.

Sets the contents of the `Accept-Encoding:` header sent in an HTTP request,
and enables decoding of a response when a `Content-Encoding:` header is
received.

libcurl potentially supports several different compressed encodings depending
on what support that 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,
(since curl 7.57.0) *br* which is brotli and (since curl 7.72.0) *zstd* 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 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 a
`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. You might want to limit using this option
to only known and trusted sites using secure protocols, perhaps in combination
with CURLOPT_MAXFILESIZE_LARGE(3).

# 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%

# EXAMPLE

~~~c
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%

# 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).
