1---
2c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
3SPDX-License-Identifier: curl
4Title: CURLOPT_ACCEPT_ENCODING
5Section: 3
6Source: libcurl
7See-also:
8  - CURLOPT_HTTPHEADER (3)
9  - CURLOPT_HTTP_CONTENT_DECODING (3)
10  - CURLOPT_TRANSFER_ENCODING (3)
11Protocol:
12  - HTTP
13---
14
15# NAME
16
17CURLOPT_ACCEPT_ENCODING - automatic decompression of HTTP downloads
18
19# SYNOPSIS
20
21~~~c
22#include <curl/curl.h>
23
24CURLcode curl_easy_setopt(CURL *handle, CURLOPT_ACCEPT_ENCODING, char *enc);
25~~~
26
27# DESCRIPTION
28
29Pass a char pointer argument specifying what encoding you would like.
30
31Sets the contents of the Accept-Encoding: header sent in an HTTP request, and
32enables decoding of a response when a Content-Encoding: header is received.
33
34libcurl potentially supports several different compressed encodings depending
35on what support that has been built-in.
36
37To aid applications not having to bother about what specific algorithms this
38particular libcurl build supports, libcurl allows a zero-length string to be
39set ("") to ask for an Accept-Encoding: header to be used that contains all
40built-in supported encodings.
41
42Alternatively, you can specify exactly the encoding or list of encodings you
43want in the response. The following encodings are supported: *identity*,
44meaning non-compressed, *deflate* which requests the server to compress
45its response using the zlib algorithm, *gzip* which requests the gzip
46algorithm, (since curl 7.57.0) *br* which is brotli and (since curl
477.72.0) *zstd* which is zstd. Provide them in the string as a
48comma-separated list of accepted encodings, like: **"br, gzip, deflate"**.
49
50Set CURLOPT_ACCEPT_ENCODING(3) to NULL to explicitly disable it, which
51makes libcurl not send an Accept-Encoding: header and not decompress received
52contents automatically.
53
54You can also opt to just include the Accept-Encoding: header in your request
55with CURLOPT_HTTPHEADER(3) but then there is no automatic decompressing
56when receiving data.
57
58This is a request, not an order; the server may or may not do it. This option
59must be set (to any non-NULL value) or else any unsolicited encoding done by
60the server is ignored.
61
62Servers might respond with Content-Encoding even without getting a
63Accept-Encoding: in the request. Servers might respond with a different
64Content-Encoding than what was asked for in the request.
65
66The Content-Length: servers send for a compressed response is supposed to
67indicate the length of the compressed content so when auto decoding is enabled
68it may not match the sum of bytes reported by the write callbacks (although,
69sending the length of the non-compressed content is a common server mistake).
70
71The application does not have to keep the string around after setting this
72option.
73
74# DEFAULT
75
76NULL
77
78# EXAMPLE
79
80~~~c
81int main(void)
82{
83  CURL *curl = curl_easy_init();
84  if(curl) {
85    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
86
87    /* enable all supported built-in compressions */
88    curl_easy_setopt(curl, CURLOPT_ACCEPT_ENCODING, "");
89
90    /* Perform the request */
91    curl_easy_perform(curl);
92  }
93}
94~~~
95
96# AVAILABILITY
97
98This option was called CURLOPT_ENCODING before 7.21.6
99
100The specific libcurl you are using must have been built with zlib to be able to
101decompress gzip and deflate responses, with the brotli library to
102decompress brotli responses and with the zstd library to decompress zstd
103responses.
104
105# RETURN VALUE
106
107Returns CURLE_OK if the option is supported, CURLE_UNKNOWN_OPTION if not, or
108CURLE_OUT_OF_MEMORY if there was insufficient heap space.
109