Several methods are available:

• Upload file contents directly, using the $1file parameter.
• Upload the file in pieces, using the $1filesize, $1chunk, and $1offset parameters.
• Have the MediaWiki server fetch a file from a URL, using the $1url parameter.
• Complete an earlier upload that failed due to warnings, using the $1filekey parameter.

Note that the HTTP POST must be done as a file upload (i.e. using multipart/form-data) when sending the $1file.