Things this must do:

• Check filesystem to ensure uploads will fit before accepting the upload
• Check content length when upload starts to ensure the upload will fit
• Stream upload direct to disk (don't keep in memory!)
• Limit upload size to 1GB for attachments, and 100mb for export (or some other sane numbers)
• Once file is uploaded, detect the type of file of the upload (gzip, zip, bzip2, plain text, tar.gz, tar.bz2), calculate size of decompressed content, and fail if decompressing would fill disk
• Decompress content
• Clean up appropriately if anything fails