curl_formadd - add a section to a multipart form POST
#include <curl/curl.h>
CURLFORMcode curl_formadd(struct curl_httppost **firstitem,
struct curl_httppost **lastitem, ...);
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
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 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 will 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.
- 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_NAMELENGTH. The name
is not allowed to contain zero-valued bytes. 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 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
application 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 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 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 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.
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 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.
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,
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 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 generates. 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.
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);
Deprecated in 7.56.0. Before this release, field names were allowed to contain
zero-valued bytes. The pseudo-filename "-" to read stdin is
discouraged although still supported, but data is not read before being
actually sent: the effective data size can then not be automatically
determined, resulting in a chunked encoding transfer. Backslashes and double
quotes in field and file names are now escaped before transmission.
0 means everything was OK, non-zero means an error occurred corresponding to a
CURL_FORMADD_* constant defined in
<curl/curl.h>
curl_easy_setopt(3),
curl_formfree(3),
curl_mime_init(3)