CURLOPT\_MIME\_OPTIONS(3) Library Functions Manual CURLOPT\_MIME\_OPTIONS(3)

# [NAME](#NAME)

CURLOPT\_MIME\_OPTIONS - set MIME option flags

# [SYNOPSIS](#SYNOPSIS)

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

# [DESCRIPTION](#DESCRIPTION)

Pass a long that holds a bitmask of options. Each bit is a boolean flag used while encoding a MIME tree or multipart form data.

Available bits are:

[CURLMIMEOPT\_FORMESCAPE](#CURLMIMEOPT_FORMESCAPE)

Tells libcurl to escape multipart form field and filenames using the backslash-escaping algorithm rather than percent-encoding (HTTP only).

Backslash-escaping consists in preceding backslashes and double quotes with a backslash. Percent encoding maps all occurrences of double quote, carriage return and line feed to %22, %0D and %0A respectively.

Before version 7.81.0, percent-encoding was never applied.

HTTP browsers used to do backslash-escaping in the past but have over time transitioned to use percent-encoding. This option allows one to address server-side applications that have not yet have been converted.

As an example, consider field or filename *strangename"kind*. When the containing multipart form is sent, this is normally transmitted as *strangename%22kind*. When this option is set, it is sent as *strangename"kind*.

# [DEFAULT](#DEFAULT)

0, meaning disabled.

# [PROTOCOLS](#PROTOCOLS)

This functionality affects http, imap and smtp

# [EXAMPLE](#EXAMPLE)

```
int main(void)
{


  CURL *curl = curl_easy_init();


  curl_mime *form = NULL;


  if(curl) {


    CURLcode result = CURLE_OK;


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


    curl_easy_setopt(curl, CURLOPT_MIME_OPTIONS, CURLMIMEOPT_FORMESCAPE);


    form = curl_mime_init(curl);


    if(form) {


      curl_mimepart *part = curl_mime_addpart(form);


      if(part) {


        curl_mime_filedata(part, "strange\\file\\name");


        curl_mime_name(part, "strange\"field\"name");


        curl_easy_setopt(curl, CURLOPT_MIMEPOST, form);


        /* Perform the request */


        result = curl_easy_perform(curl);


      }


    }


    curl_easy_cleanup(curl);


    curl_mime_free(form);


  }
}
```

# [HISTORY](#HISTORY)

**CURLMIMEOPT\_FORMESCAPE** macro became *long* type 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 7.81.0

# [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\_HTTPPOST**(3)](/man/os/curl/CURLOPT_HTTPPOST.3), [**CURLOPT\_MIMEPOST**(3)](/man/os/curl/CURLOPT_MIMEPOST.3)

2026-10-22 libcurl

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Document: CURLOPT_MIME_OPTIONS(3) from curl 8.23.0-r2 (Chainguard OS)
Source: https://github.com/curl/curl.git