CURLOPT_CUSTOMREQUEST man page
CURLOPT_CUSTOMREQUEST — custom string for request
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_CUSTOMREQUEST, char *request);
Pass a pointer to a zero terminated string as parameter.
When you change the request method by setting CURLOPT_CUSTOMREQUEST(3) to something, you don't actually change how libcurl behaves or acts in regards to the particular request method, it will only change the actual string sent in the request.
Restore to the internal default by setting this to NULL.
This option can be used to specify the request:
Instead of GET or HEAD when performing HTTP based requests. This is particularly useful, for example, for performing a HTTP DELETE request.
When you tell libcurl to do a HEAD request, but then specify a GET though a custom request libcurl will still act as if it sent a HEAD. To switch to a proper HEAD use CURLOPT_NOBODY(3), to switch to a proper POST use CURLOPT_POST(3) or CURLOPT_POSTFIELDS(3) and to switch to a proper GET use CURLOPT_HTTPGET(3).
Many people have wrongly used this option to replace the entire request with their own, including multiple headers and POST contents. While that might work in many cases, it will cause libcurl to send invalid requests and it could possibly confuse the remote server badly. Use CURLOPT_POST(3) and CURLOPT_POSTFIELDS(3) to set POST data. Use CURLOPT_HTTPHEADER(3) to replace or extend the set of headers sent by libcurl. Use CURLOPT_HTTP_VERSION(3) to change HTTP version.
Instead of LIST and NLST when performing FTP directory listings.
Instead of LIST when issuing IMAP based requests.
Instead of LIST and RETR when issuing POP3 based requests.
When you tell libcurl to use a custom request it will behave like a LIST or RETR command was sent where it expects data to be returned by the server. As such CURLOPT_NOBODY(3) should be used when specifying commands such as DELE and NOOP for example.
Instead of a HELP or VRFY when issuing SMTP based requests.
Normally a multiline response is returned which can be used, in conjunction with CURLOPT_MAIL_RCPT(3), to specify an EXPN request. If the CURLOPT_NOBODY(3) option is specified then the request can be used to issue NOOP and RSET commands.
HTTP, FTP, IMAP, POP3 and SMTP
IMAP is supported since 7.30.0, POP3 since 7.26.0 and SMTP since 7.34.0.
Returns CURLE_OK if the option is supported, CURLE_UNKNOWN_OPTION if not, or CURLE_OUT_OF_MEMORY if there was insufficient heap space.
curl_easy_setopt(3), CURLOPT_DIRLISTONLY(3), CURLOPT_HTTPHEADER(3), libcurl-errors(3), libcurl-tutorial(3).