Provided by: libcurl4-doc_7.47.0-1ubuntu2.19_all 
NAME
curl_formadd - add a section to a multipart/formdata HTTP POST
SYNOPSIS
#include <curl/curl.h>
CURLFORMcode curl_formadd(struct curl_httppost ** firstitem, struct curl_httppost ** lastitem, ...);
DESCRIPTION
curl_formadd() is used to append sections when building a multipart/formdata HTTP POST (sometimes
referred to as RFC2388-style posts). Append one section at a time until you've added all the sections you
want included and then you pass the firstitem pointer as parameter to CURLOPT_HTTPPOST(3). lastitem is
set after each curl_formadd(3) call and on repeated invokes it should be left as set to allow repeated
invokes to find the end of the list faster.
After the lastitem pointer follow the real arguments.
The pointers firstitem and lastitem should both be pointing to NULL in the first call to this function.
All list-data will be allocated by the function itself. You must call curl_formfree(3) on the firstitem
after the form post has been done to free the resources.
Using POST with HTTP 1.1 implies the use of a "Expect: 100-continue" header. You can disable this header
with CURLOPT_HTTPHEADER(3) as usual.
First, there are some basics you need to understand about multipart/formdata posts. Each part consists of
at least a NAME and a CONTENTS part. If the part is made for file upload, there are also a stored
CONTENT-TYPE and a FILENAME. Below, we'll discuss what options you use to set these properties in the
parts you want to add to your post.
The options listed first are for making normal parts. The options from CURLFORM_FILE through
CURLFORM_BUFFERLENGTH are for file upload parts.
OPTIONS
CURLFORM_COPYNAME
followed by a string which provides the name of this part. libcurl copies the string so your
application doesn't need to keep it around after this function call. If the name isn't NUL-
terminated, or if you'd like it to contain zero bytes, you must set its length with
CURLFORM_NAMELENGTH. The copied data will be freed by curl_formfree(3).
CURLFORM_PTRNAME
followed by a string which provides the name of this part. libcurl will use the pointer and refer
to the data in your application, so you must make sure it remains until curl no longer needs it.
If the name isn't NUL-terminated, or if you'd like it to contain zero bytes, you must set its
length with CURLFORM_NAMELENGTH.
CURLFORM_COPYCONTENTS
followed by a pointer to the contents of this part, the actual data to send away. libcurl copies
the provided data, so your application doesn't need to keep it around after this function call. If
the data isn't null terminated, or if you'd like it to contain zero bytes, you must set the length
of the name with CURLFORM_CONTENTSLENGTH. The copied data will be freed by curl_formfree(3).
CURLFORM_PTRCONTENTS
followed by a pointer to the contents of this part, the actual data to send away. libcurl will use
the pointer and refer to the data in your application, so you must make sure it remains until curl
no longer needs it. If the data isn't NUL-terminated, or if you'd like it to contain zero bytes,
you must set its length with CURLFORM_CONTENTSLENGTH.
CURLFORM_CONTENTLEN
followed by a curl_off_t value giving the length of the contents. Note that for CURLFORM_STREAM
contents, this option is mandatory.
If you pass a 0 (zero) for this option, libcurl will instead do a strlen() on the contents to
figure out the size. If you really want to send a zero byte content then you must make sure
strlen() on the data pointer returns zero.
(Option added in 7.46.0)
CURLFORM_CONTENTSLENGTH
(This option is deprecated. Use CURLFORM_CONTENTLEN instead!)
followed by a long giving the length of the contents. Note that for CURLFORM_STREAM contents, this
option is mandatory.
If you pass a 0 (zero) for this option, libcurl will instead do a strlen() on the contents to
figure out the size. If you really want to send a zero byte content then you must make sure
strlen() on the data pointer returns zero.
CURLFORM_FILECONTENT
followed by a filename, causes that file to be read and its contents used as data in this part.
This part does not automatically become a file upload part simply because its data was read from a
file.
CURLFORM_FILE
followed by a filename, makes this part a file upload part. It sets the filename field to the
basename of the provided filename, it reads the contents of the file and passes them as data and
sets the content-type if the given file match one of the internally known file extensions. For
CURLFORM_FILE the user may send one or more files in one part by providing multiple CURLFORM_FILE
arguments each followed by the filename (and each CURLFORM_FILE is allowed to have a
CURLFORM_CONTENTTYPE).
The given upload file has to exist in its full in the file system already when the upload starts,
as libcurl needs to read the correct file size beforehand.
CURLFORM_CONTENTTYPE
is used in combination with CURLFORM_FILE. Followed by a pointer to a string which provides the
content-type for this part, possibly instead of an internally chosen one.
CURLFORM_FILENAME
is used in combination with CURLFORM_FILE. Followed by a pointer to a string, it tells libcurl to
use the given string as the filename in the file upload part instead of the actual file name.
CURLFORM_BUFFER
is used for custom file upload parts without use of CURLFORM_FILE. It tells libcurl that the file
contents are already present in a buffer. The parameter is a string which provides the filename
field in the content header.
CURLFORM_BUFFERPTR
is used in combination with CURLFORM_BUFFER. The parameter is a pointer to the buffer to be
uploaded. This buffer must not be freed until after curl_easy_cleanup(3) is called. You must also
use CURLFORM_BUFFERLENGTH to set the number of bytes in the buffer.
CURLFORM_BUFFERLENGTH
is used in combination with CURLFORM_BUFFER. The parameter is a long which gives the length of the
buffer.
CURLFORM_STREAM
Tells libcurl to use the CURLOPT_READFUNCTION(3) callback to get data. The parameter you pass to
CURLFORM_STREAM is the pointer passed on to the read callback's fourth argument. If you want the
part to look like a file upload one, set the CURLFORM_FILENAME parameter as well. Note that when
using CURLFORM_STREAM, CURLFORM_CONTENTSLENGTH must also be set with the total expected length of
the part. (Option added in libcurl 7.18.2)
CURLFORM_ARRAY
Another possibility to send options to curl_formadd() is the CURLFORM_ARRAY option, that passes a
struct curl_forms array pointer as its value. Each curl_forms structure element has a
CURLformoption and a char pointer. The final element in the array must be a CURLFORM_END. All
available options can be used in an array, except the CURLFORM_ARRAY option itself! The last
argument in such an array must always be CURLFORM_END.
CURLFORM_CONTENTHEADER
specifies extra headers for the form POST section. This takes a curl_slist prepared in the usual
way using curl_slist_append and appends the list of headers to those libcurl automatically
generates. The list must exist while the POST occurs, if you free it before the post completes you
may experience problems.
When you've passed the HttpPost pointer to curl_easy_setopt(3) (using the CURLOPT_HTTPPOST(3)
option), you must not free the list until after you've called curl_easy_cleanup(3) for the curl
handle.
See example below.
RETURN VALUE
0 means everything was ok, non-zero means an error occurred corresponding to a CURL_FORMADD_* constant
defined in <curl/curl.h>
EXAMPLE
struct curl_httppost* post = NULL;
struct curl_httppost* last = NULL;
char namebuffer[] = "name buffer";
long namelength = strlen(namebuffer);
char buffer[] = "test buffer";
char htmlbuffer[] = "<HTML>test buffer</HTML>";
long htmlbufferlength = strlen(htmlbuffer);
struct curl_forms forms[3];
char file1[] = "my-face.jpg";
char file2[] = "your-face.jpg";
/* add null character into htmlbuffer, to demonstrate that
transfers of buffers containing null characters actually work
*/
htmlbuffer[8] = '\0';
/* Add simple name/content section */
curl_formadd(&post, &last, CURLFORM_COPYNAME, "name",
CURLFORM_COPYCONTENTS, "content", CURLFORM_END);
/* Add simple name/content/contenttype section */
curl_formadd(&post, &last, CURLFORM_COPYNAME, "htmlcode",
CURLFORM_COPYCONTENTS, "<HTML></HTML>",
CURLFORM_CONTENTTYPE, "text/html", CURLFORM_END);
/* Add name/ptrcontent section */
curl_formadd(&post, &last, CURLFORM_COPYNAME, "name_for_ptrcontent",
CURLFORM_PTRCONTENTS, buffer, CURLFORM_END);
/* Add ptrname/ptrcontent section */
curl_formadd(&post, &last, CURLFORM_PTRNAME, namebuffer,
CURLFORM_PTRCONTENTS, buffer, CURLFORM_NAMELENGTH,
namelength, CURLFORM_END);
/* Add name/ptrcontent/contenttype section */
curl_formadd(&post, &last, CURLFORM_COPYNAME, "html_code_with_hole",
CURLFORM_PTRCONTENTS, htmlbuffer,
CURLFORM_CONTENTSLENGTH, htmlbufferlength,
CURLFORM_CONTENTTYPE, "text/html", CURLFORM_END);
/* Add simple file section */
curl_formadd(&post, &last, CURLFORM_COPYNAME, "picture",
CURLFORM_FILE, "my-face.jpg", CURLFORM_END);
/* Add file/contenttype section */
curl_formadd(&post, &last, CURLFORM_COPYNAME, "picture",
CURLFORM_FILE, "my-face.jpg",
CURLFORM_CONTENTTYPE, "image/jpeg", CURLFORM_END);
/* Add two file section */
curl_formadd(&post, &last, CURLFORM_COPYNAME, "pictures",
CURLFORM_FILE, "my-face.jpg",
CURLFORM_FILE, "your-face.jpg", CURLFORM_END);
/* Add two file section using CURLFORM_ARRAY */
forms[0].option = CURLFORM_FILE;
forms[0].value = file1;
forms[1].option = CURLFORM_FILE;
forms[1].value = file2;
forms[2].option = CURLFORM_END;
/* Add a buffer to upload */
curl_formadd(&post, &last,
CURLFORM_COPYNAME, "name",
CURLFORM_BUFFER, "data",
CURLFORM_BUFFERPTR, record,
CURLFORM_BUFFERLENGTH, record_length,
CURLFORM_END);
/* no option needed for the end marker */
curl_formadd(&post, &last, CURLFORM_COPYNAME, "pictures",
CURLFORM_ARRAY, forms, CURLFORM_END);
/* Add the content of a file as a normal post text value */
curl_formadd(&post, &last, CURLFORM_COPYNAME, "filecontent",
CURLFORM_FILECONTENT, ".bashrc", CURLFORM_END);
/* Set the form info */
curl_easy_setopt(curl, CURLOPT_HTTPPOST, post);
SEE ALSO
curl_easy_setopt(3), curl_formfree(3)