CURLOPT\_HEADEROPT(3) Library Functions Manual CURLOPT\_HEADEROPT(3)

# [NAME](#NAME)

CURLOPT\_HEADEROPT - send HTTP headers to both proxy and host or separately

# [SYNOPSIS](#SYNOPSIS)

```
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HEADEROPT, long bitmask);
```

# [DESCRIPTION](#DESCRIPTION)

Pass a long that is a bitmask of options of how to deal with headers. The two mutually exclusive options are:

**CURLHEADER\_UNIFIED** - the headers specified in [*CURLOPT\_HTTPHEADER(3)*](/man/os/curl/CURLOPT_HTTPHEADER.3) are used in requests both to servers and proxies. With this option enabled, [*CURLOPT\_PROXYHEADER(3)*](/man/os/curl/CURLOPT_PROXYHEADER.3) does not have any effect.

**CURLHEADER\_SEPARATE** - makes [*CURLOPT\_HTTPHEADER(3)*](/man/os/curl/CURLOPT_HTTPHEADER.3) headers only get sent to a server and not to a proxy. Proxy headers must be set with [*CURLOPT\_PROXYHEADER(3)*](/man/os/curl/CURLOPT_PROXYHEADER.3) to get used. Note that if a non-CONNECT request is sent to a proxy, libcurl sends both server headers and proxy headers. When doing CONNECT, libcurl sends [*CURLOPT\_PROXYHEADER(3)*](/man/os/curl/CURLOPT_PROXYHEADER.3) headers only to the proxy and then [*CURLOPT\_HTTPHEADER(3)*](/man/os/curl/CURLOPT_HTTPHEADER.3) headers only to the server.

# [DEFAULT](#DEFAULT)

CURLHEADER\_SEPARATE (changed in 7.42.1, used CURLHEADER\_UNIFIED before then)

# [PROTOCOLS](#PROTOCOLS)

This functionality affects http only

# [EXAMPLE](#EXAMPLE)

```
int main(void)
{


  CURL *curl = curl_easy_init();


  if(curl) {


    CURLcode result;


    struct curl_slist *list;


    list = curl_slist_append(NULL, "Shoesize: 10");


    list = curl_slist_append(list, "Accept:");


    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");


    curl_easy_setopt(curl, CURLOPT_PROXY, "http://localhost:8080");


    curl_easy_setopt(curl, CURLOPT_HTTPHEADER, list);


    /* HTTPS over a proxy makes a separate CONNECT to the proxy, so tell


       libcurl to not send the custom headers to the proxy. Keep them


       separate. */


    curl_easy_setopt(curl, CURLOPT_HEADEROPT, CURLHEADER_SEPARATE);


    result = curl_easy_perform(curl);


    curl_slist_free_all(list);


    curl_easy_cleanup(curl);


  }
}
```

# [HISTORY](#HISTORY)

**CURLHEADER\_*** macros became *long* types in 8.16.0, prior to this version a *long* cast was necessary when passed to [*curl\_easy\_setopt(3)*](/man/os/curl/curl_easy_setopt.3).

# [AVAILABILITY](#AVAILABILITY)

Added in curl 7.37.0

# [RETURN VALUE](#RETURN_VALUE)

[*curl\_easy\_setopt(3)*](/man/os/curl/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)*](/man/os/curl/libcurl-errors.3).

# [SEE ALSO](#SEE_ALSO)

[**CURLOPT\_HTTPHEADER**(3)](/man/os/curl/CURLOPT_HTTPHEADER.3), [**CURLOPT\_PROXYHEADER**(3)](/man/os/curl/CURLOPT_PROXYHEADER.3)

2026-09-24 libcurl

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Document: CURLOPT_HEADEROPT(3) from curl 8.22.0-r3 (Chainguard OS)
Source: https://github.com/curl/curl.git