1---
2c: Copyright (C) Daniel Stenberg, <daniel.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)
11---
12
13# NAME
14
15CURLOPT_ACCEPT_ENCODING - automatic decompression of HTTP downloads
16
17# SYNOPSIS
18
19~~~c
20#include <curl/curl.h>
21
22CURLcode curl_easy_setopt(CURL *handle, CURLOPT_ACCEPT_ENCODING, char *enc);
23~~~
24
25# DESCRIPTION
26
27Pass a char pointer argument specifying what encoding you would like.
28
29Sets the contents of the Accept-Encoding: header sent in an HTTP request, and
30enables decoding of a response when a Content-Encoding: header is received.
31
32libcurl potentially supports several different compressed encodings depending
33on what support that has been built-in.
34
35To aid applications not having to bother about what specific algorithms this
36particular libcurl build supports, libcurl allows a zero-length string to be
37set ("") to ask for an Accept-Encoding: header to be used that contains all
38built-in supported encodings.
39
40Alternatively, you can specify exactly the encoding or list of encodings you
41want in the response. The following encodings are supported: *identity*,
42meaning non-compressed, *deflate* which requests the server to compress
43its response using the zlib algorithm, *gzip* which requests the gzip
44algorithm, (since curl 7.57.0) *br* which is brotli and (since curl
457.72.0) *zstd* which is zstd. Provide them in the string as a
46comma-separated list of accepted encodings, like: **"br, gzip, deflate"**.
47
48Set CURLOPT_ACCEPT_ENCODING(3) to NULL to explicitly disable it, which
49makes libcurl not send an Accept-Encoding: header and not decompress received
50contents automatically.
51
52You can also opt to just include the Accept-Encoding: header in your request
53with CURLOPT_HTTPHEADER(3) but then there is no automatic decompressing
54when receiving data.
55
56This is a request, not an order; the server may or may not do it. This option
57must be set (to any non-NULL value) or else any unsolicited encoding done by
58the server is ignored.
59
60Servers might respond with Content-Encoding even without getting a
61Accept-Encoding: in the request. Servers might respond with a different
62Content-Encoding than what was asked for in the request.
63
64The Content-Length: servers send for a compressed response is supposed to
65indicate the length of the compressed content so when auto decoding is enabled
66it may not match the sum of bytes reported by the write callbacks (although,
67sending the length of the non-compressed content is a common server mistake).
68
69The application does not have to keep the string around after setting this
70option.
71
72# DEFAULT
73
74NULL
75
76# PROTOCOLS
77
78HTTP
79
80# EXAMPLE
81
82~~~c
83int main(void)
84{
85  CURL *curl = curl_easy_init();
86  if(curl) {
87    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
88
89    /* enable all supported built-in compressions */
90    curl_easy_setopt(curl, CURLOPT_ACCEPT_ENCODING, "");
91
92    /* Perform the request */
93    curl_easy_perform(curl);
94  }
95}
96~~~
97
98# AVAILABILITY
99
100This option was called CURLOPT_ENCODING before 7.21.6
101
102The specific libcurl you are using must have been built with zlib to be able to
103decompress gzip and deflate responses, with the brotli library to
104decompress brotli responses and with the zstd library to decompress zstd
105responses.
106
107# RETURN VALUE
108
109Returns CURLE_OK if the option is supported, CURLE_UNKNOWN_OPTION if not, or
110CURLE_OUT_OF_MEMORY if there was insufficient heap space.
111