On Mon, Oct 24, 2011 at 8:55 AM, Gavin Andresen <gavinandresen@gmail.com> wrote:

If you assume the client has all previous transactions, then you could
get the transaction input's prevout (from the memory pool or disk) and
then ExtractAddress() from it. That is probably a bad idea for
listtransactions, since fetching all the previous inputs from disk
just so you can check to see if they're 'green' violates the "a
feature shouldn't cost anything if it is not being used" design
principle.

Are there current users of gettransaction for whom the performance penalty would be problematic? If so, perhaps gettransaction could take an optional second argument includeinputaddresses which defaults to false.

Michael