HTTP multipart/form-data parser
Initializes a form-data encoded body handler for
http request streams. Returning this handler function from inside the
RequestCallback function of an
http server initiates parsing of the
multipart/form-data-encoded request body.
onPart will be called for every request part (i.e., form field), including its body (or portion thereof), headers, and name (if present in the headers).
onPart may be called again with more
body content and the same
callback is issued when request processing is complete and a response is required. If an error occurred, the
error argument is its HTTP status code.