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. 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) 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 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_CONTENTSLENGTH
followed by a long giving the length of the contents. Note that
for CURLFORM_STREAM contents, this option is mandatory.
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).
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 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 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)