Maybe check the hypothetic.org docs on file transfers.
EDIT: The name's sent in the invitation as one of the little parameter thingies, under "Application-File". Filesize is under "Application-Size". (note that this is not extremely up to date, there may have been changes but it is likely to be the same or very similar)
Example invitation:
code:
>>> MSG 12 N 294
MIME-Version: 1.0
Content-Type: text/x-msmsgsinvite; charset=UTF-8
Application-Name: File Transfer
Application-GUID: {5D3E02AB-6190-11d3-BBBB-00C04F795683}
Invitation-Command: INVITE
Invitation-Cookie: 85366
Application-File: Autoexec.bat
Application-FileSize: 187
Connectivity: N
Source: Hypothetic Documentation