curl_formadd(3) libcurl Manual curl_formadd(3)
curl_formadd - add a section to a multipart/formdata HTTP POST
CURLFORMcode curl_formadd(struct curl_httppost ** firstitem, struct curl_httppost ** lastitem, ...);
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 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 firstitemP 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
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).
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.
followed by a pointer to the contents of this part, the actual data to send away. libcurl copies the provided data, so your applica-
tion 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).
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.
followed by a long giving the length of the contents. Note that for CURLFORM_STREAM contents, this option is mandatory.
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.
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).
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.
is used in combination with CURLFORM_FILE. Followed by a pointer to a string, it tells libcurl to use the given string as the file-
name in the file upload part instead of the actual file name.
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.
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.
is used in combination with CURLFORM_BUFFER. The parameter is a long which gives the length of the buffer.
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)
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 CURL-
FORM_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.
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.
0 means everything was ok, non-zero means an error occurred corresponding to a CURL_FORMADD_* constant defined in <curl/curl.h>
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;
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 = '