(I realize now this should be in bugs section...)
Rejetto in hfs.events can you make a section called [upload] or something similar where macros are executed before an upload starts? For example, the following code under [request] does NOT stop an upload from occuring:
{.if|{.count substring|multipart/form-data|{.header|Content-Type.}.}|{:{.disconnect.}:}.}
I get this in the log:
if|1|{:{.disconnect.}{.break.}:}
{.disconnect.}{.break.}
disconnect
<div class=macroerror>macro error: disconnect<br>not supported or illegal parameters</div>
break