curl / libcurl / API / curl_easy_setopt / CURLOPT_POST

CURLOPT_POST explained

Name

CURLOPT_POST - make an HTTP POST

Synopsis

#include <curl/curl.h>
 
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_POST, long post);

Description

A parameter set to 1 tells libcurl to do a regular HTTP post. This also makes libcurl use a "Content-Type: application/x-www-form-urlencoded" header. This is the most commonly used POST method.

Use one of CURLOPT_POSTFIELDS or CURLOPT_COPYPOSTFIELDS options to specify what data to post and CURLOPT_POSTFIELDSIZE or CURLOPT_POSTFIELDSIZE_LARGE to set the data size.

Optionally, you can provide data to POST using the CURLOPT_READFUNCTION and CURLOPT_READDATA options but then you must make sure to not set CURLOPT_POSTFIELDS to anything but NULL. When providing data with a callback, you must transmit it using chunked transfer-encoding or you must set the size of the data with the CURLOPT_POSTFIELDSIZE or CURLOPT_POSTFIELDSIZE_LARGE options. To enable chunked encoding, you simply pass in the appropriate Transfer-Encoding header, see the post-callback.c example.

You can override the default POST Content-Type: header by setting your own with CURLOPT_HTTPHEADER.

Using POST with HTTP 1.1 implies the use of a "Expect: 100-continue" header. You can disable this header with CURLOPT_HTTPHEADER as usual.

If you use POST to an HTTP 1.1 server, you can send data without knowing the size before starting the POST if you use chunked encoding. You enable this by adding a header like "Transfer-Encoding: chunked" with CURLOPT_HTTPHEADER. With HTTP 1.0 or without chunked transfer, you must specify the size in the request. (Since 7.66.0, libcurl automatically uses chunked encoding for POSTs if the size is unknown.)

When setting CURLOPT_POST to 1, libcurl automatically sets CURLOPT_NOBODY and CURLOPT_HTTPGET to 0.

If you issue a POST request and then want to make a HEAD or GET using the same reused handle, you must explicitly set the new request type using CURLOPT_NOBODY or CURLOPT_HTTPGET or similar.

When setting CURLOPT_POST to 0, libcurl resets the request type to the default to disable the POST. Typically that means gets reset to GET. Instead you should set a new request type explicitly as described above.

Default

0, disabled

Protocols

This functionality affects http only

Example

int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    CURLcode res;
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/foo.bin");
    curl_easy_setopt(curl, CURLOPT_POST, 1L);
 
    /* set up the read callback with CURLOPT_READFUNCTION */
 
    res = curl_easy_perform(curl);
 
    curl_easy_cleanup(curl);
  }
}

Availability

Added in curl 7.1

Return value

Returns CURLE_OK if HTTP is supported, and CURLE_UNKNOWN_OPTION if not.