1---
2c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
3SPDX-License-Identifier: curl
4Title: CURLOPT_HTTPHEADER
5Section: 3
6Source: libcurl
7Protocol:
8  - HTTP
9  - SMTP
10  - IMAP
11See-also:
12  - CURLOPT_CUSTOMREQUEST (3)
13  - CURLOPT_HEADER (3)
14  - CURLOPT_HEADEROPT (3)
15  - CURLOPT_MIMEPOST (3)
16  - CURLOPT_PROXYHEADER (3)
17  - curl_mime_init (3)
18---
19
20# NAME
21
22CURLOPT_HTTPHEADER - set of HTTP headers
23
24# SYNOPSIS
25
26~~~c
27#include <curl/curl.h>
28
29CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HTTPHEADER,
30                          struct curl_slist *headers);
31~~~
32
33# DESCRIPTION
34
35Pass a pointer to a linked list of HTTP headers to pass to the server and/or
36proxy in your HTTP request. The same list can be used for both host and proxy
37requests!
38
39When used within an IMAP or SMTP request to upload a MIME mail, the given
40header list establishes the document-level MIME headers to prepend to the
41uploaded document described by CURLOPT_MIMEPOST(3). This does not affect
42raw mail uploads.
43
44The linked list should be a fully valid list of **struct curl_slist**
45structs properly filled in. Use curl_slist_append(3) to create the list
46and curl_slist_free_all(3) to clean up an entire list. If you add a
47header that is otherwise generated and used by libcurl internally, your added
48header is used instead. If you add a header with no content as in 'Accept:'
49(no data on the right side of the colon), the internally used header is
50disabled/removed. With this option you can add new headers, replace internal
51headers and remove internal headers. To add a header with no content (nothing
52to the right side of the colon), use the form 'name;' (note the ending
53semicolon).
54
55The headers included in the linked list **must not** be CRLF-terminated,
56because libcurl adds CRLF after each header item itself. Failure to comply
57with this might result in strange behavior. libcurl passes on the verbatim
58strings you give it, without any filter or other safe guards. That includes
59white space and control characters.
60
61The first line in an HTTP request (containing the method, usually a GET or
62POST) is not a header and cannot be replaced using this option. Only the lines
63following the request-line are headers. Adding this method line in this list
64of headers only causes your request to send an invalid header. Use
65CURLOPT_CUSTOMREQUEST(3) to change the method.
66
67When this option is passed to curl_easy_setopt(3), libcurl does not copy
68the entire list so you **must** keep it around until you no longer use this
69*handle* for a transfer before you call curl_slist_free_all(3) on
70the list.
71
72Pass a NULL to this option to reset back to no custom headers.
73
74The most commonly replaced HTTP headers have "shortcuts" in the options
75CURLOPT_COOKIE(3), CURLOPT_USERAGENT(3) and
76CURLOPT_REFERER(3). We recommend using those.
77
78There is an alternative option that sets or replaces headers only for requests
79that are sent with CONNECT to a proxy: CURLOPT_PROXYHEADER(3). Use
80CURLOPT_HEADEROPT(3) to control the behavior.
81
82# SPECIFIC HTTP HEADERS
83
84Setting some specific headers causes libcurl to act differently.
85
86## Host:
87
88The specified hostname is used for cookie matching if the cookie engine is
89also enabled for this transfer. If the request is done over HTTP/2 or HTTP/3,
90the custom hostname is instead used in the ":authority" header field and
91Host: is not sent at all over the wire.
92
93## Transfer-Encoding: chunked
94
95Tells libcurl the upload is to be done using this chunked encoding instead of
96providing the Content-Length: field in the request.
97
98# SPECIFIC MIME HEADERS
99
100When used to build a MIME email for IMAP or SMTP, the following document-level
101headers can be set to override libcurl-generated values:
102
103## Mime-Version:
104
105Tells the parser at the receiving site how to interpret the MIME framing.
106It defaults to "1.0" and should normally not be altered.
107
108## Content-Type:
109
110Indicates the document's global structure type. By default, libcurl sets it
111to "multipart/mixed", describing a document made of independent parts. When a
112MIME mail is only composed of alternative representations of the same data
113(i.e.: HTML and plain text), this header must be set to "multipart/alternative".
114In all cases the value must be of the form "multipart/*" to respect the
115document structure and may not include the "boundary=" parameter.
116
117Other specific headers that do not have a libcurl default value but are
118strongly desired by mail delivery and user agents should also be included.
119These are "From:", "To:", "Date:" and "Subject:" among others and their
120presence and value is generally checked by anti-spam utilities.
121
122# SECURITY CONCERNS
123
124By default, this option makes libcurl send the given headers in all HTTP
125requests done by this handle. You should therefore use this option with
126caution if you for example connect to the remote site using a proxy and a
127CONNECT request, you should to consider if that proxy is supposed to also get
128the headers. They may be private or otherwise sensitive to leak.
129
130Use CURLOPT_HEADEROPT(3) to make the headers only get sent to where you
131intend them to get sent.
132
133Custom headers are sent in all requests done by the easy handle, which implies
134that if you tell libcurl to follow redirects
135(CURLOPT_FOLLOWLOCATION(3)), the same set of custom headers is sent in
136the subsequent request. Redirects can of course go to other hosts and thus
137those servers get all the contents of your custom headers too.
138
139Starting in 7.58.0, libcurl specifically prevents "Authorization:" headers
140from being sent to other hosts than the first used one, unless specifically
141permitted with the CURLOPT_UNRESTRICTED_AUTH(3) option.
142
143Starting in 7.64.0, libcurl specifically prevents "Cookie:" headers from being
144sent to other hosts than the first used one, unless specifically permitted
145with the CURLOPT_UNRESTRICTED_AUTH(3) option.
146
147# DEFAULT
148
149NULL
150
151# EXAMPLE
152
153~~~c
154int main(void)
155{
156  CURL *curl = curl_easy_init();
157
158  struct curl_slist *list = NULL;
159
160  if(curl) {
161    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
162
163    list = curl_slist_append(list, "Shoesize: 10");
164    list = curl_slist_append(list, "Accept:");
165
166    curl_easy_setopt(curl, CURLOPT_HTTPHEADER, list);
167
168    curl_easy_perform(curl);
169
170    curl_slist_free_all(list); /* free the list */
171  }
172}
173~~~
174
175# AVAILABILITY
176
177As long as HTTP is enabled. Use in MIME mail added in 7.56.0.
178
179# RETURN VALUE
180
181Returns CURLE_OK if HTTP is supported, and CURLE_UNKNOWN_OPTION if not.
182