www.LinuxHowtos.org

curl_formadd

Section: libcurl Manual (3)
Updated: December 28, 2016
Index Return to Main Contents

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.

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'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);