CURLOPT_MIME_OPTIONS(3) Library Functions Manual CURLOPT_MIME_OPTIONS(3)
NAME
CURLOPT_MIME_OPTIONS - set MIME option flags
SYNOPSIS
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_MIME_OPTIONS, long options);
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
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 al-
lows 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 transmit-
ted as strangename%22kind. When this option is set, it is sent as
strangename"kind.
DEFAULT
0, meaning disabled.
PROTOCOLS
This functionality affects http, imap and smtp
EXAMPLE
int main(void)
{
CURL *curl = curl_easy_init();
curl_mime *form = NULL;
if(curl) {
curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
curl_easy_setopt(curl, CURLOPT_MIME_OPTIONS, (long)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 */
curl_easy_perform(curl);
}
}
curl_easy_cleanup(curl);
curl_mime_free(form);
}
}
AVAILABILITY
Added in curl 7.81.0
RETURN VALUE
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).
SEE ALSO
CURLOPT_HTTPPOST(3), CURLOPT_MIMEPOST(3)
libcurl 2026-07-12 CURLOPT_MIME_OPTIONS(3)
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