This bug is actually a reminder about what I would like to have one day:

1) Compress a file before actually send it to save bandwidth
2) Extract a compressed file when it is received
3) Compress several files in one archive and make a single file transfer when sending more than one file
4) Extract an archive when it is received

Possible implementation:
1 and 3 are actually not implementable directly in the handler at the moment, because the size must be specified when a file transfer is created (but perhaps it is not used). We can implement it at library level (i.e. in tp-qt4).
The interface Channel.Interface.FileTransfer.Metadata can be used to let the other side know that the file is compressed.
The receiver can just extract the file when it is received.
The Metadata interface can be used to let the other side know that we support the file extraction, therefore a single file can be sent either compressed if the other side supports it, or not compressed if it doesn't.