curl_formadd(3) Library Functions Manual curl_formadd(3)
NAME
curl_formadd - add a section to a multipart form POST
SYNOPSIS
#include <curl/curl.h>
CURLFORMcode curl_formadd(struct curl_httppost **firstitem,
struct curl_httppost **lastitem, ...);
DESCRIPTION
This function is deprecated. Use curl_mime_init(3) instead.
curl_formadd() is used to append sections when building a multipart form
post. Append one section at a time until you have 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 in-
vokes 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 is allocated by the func-
tion 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 form
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 discuss what options you use to set these proper-
ties 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 does not need to
keep it around after this function call. If the name is not
null-terminated, you must set its length with CURLFORM_NAME-
LENGTH. The name is not allowed to contain zero-valued bytes. The
copied data is freed by curl_formfree(3).
CURLFORM_PTRNAME
followed by a string which provides the name of this part.
libcurl uses the pointer and refer to the data in your applica-
tion, so you must make sure it remains until curl no longer needs
it. If the name is not null-terminated, you must set its length
with CURLFORM_NAMELENGTH. The name is not allowed to contain
zero-valued bytes.
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 ap-
plication does not need to keep it around after this function
call. If the data is not null-terminated, or if you would like it
to contain zero bytes, you must set the length of the name with
CURLFORM_CONTENTSLENGTH. The copied data is freed by curl_form-
free(3).
CURLFORM_PTRCONTENTS
followed by a pointer to the contents of this part, the actual
data to send away. libcurl uses 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 is not null-terminated, or if you
would 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 calls 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 calls 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 con-
tents 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.
The specified file needs to kept around until the associated
transfer is done.
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 inter-
nally 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 cor-
rect file size beforehand.
The specified file needs to kept around until the associated
transfer is done.
CURLFORM_CONTENTTYPE
is used in combination with CURLFORM_FILE. Followed by a pointer
to a string which provides the content-type for this part, possi-
bly 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 filename.
CURLFORM_BUFFER
is used for custom file upload parts without use of CURL-
FORM_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, CURL-
FORM_CONTENTSLENGTH must also be set with the total expected
length of the part unless the formpost is sent chunked encoded.
(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 gener-
ates. The list must exist while the POST occurs, if you free it
before the post completes you may experience problems.
When you have passed the struct curl_httppost pointer to
curl_easy_setopt(3) (using the CURLOPT_HTTPPOST(3) option), you
must not free the list until after you have called
curl_easy_cleanup(3) for the curl handle.
See example below.
PROTOCOLS
This functionality affects http only
EXAMPLE
#include <string.h> /* for strlen */
static const char record[]="data in a buffer";
int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
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, sizeof(record),
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);
curl_easy_perform(curl);
curl_easy_cleanup(curl);
curl_formfree(post);
}
}
DEPRECATED
Deprecated in 7.56.0. Before this release, field names were allowed to
contain zero-valued bytes. The pseudo-filename "-" to read stdin is dis-
couraged although still supported, but data is not read before being ac-
tually sent: the effective data size can then not be automatically de-
termined, resulting in a chunked encoding transfer. Backslashes and dou-
ble quotes in field and filenames are now escaped before transmission.
AVAILABILITY
Added in curl 7.1
RETURN VALUE
0 means everything was OK, non-zero means an error occurred correspond-
ing to a CURL_FORMADD_ constant defined in <curl/curl.h>*.
SEE ALSO
curl_easy_setopt(3), curl_formfree(3), curl_mime_init(3)
libcurl 2026-07-12 curl_formadd(3)
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