On Mon, Mar 24, 2014 at 5:00 PM, Amir Taaki <genjix@???> wrote:
> Hey, I agree with the subscription stuff. I want to get rid of it and
> move towards a history polling method.
> I think it's possible to make fetch_history from a specific block height
> to be very fast. Then you will fetch_history by prefix and we have a
> superior privacy model for clients with the server.
> The problem is when new blocks arrive you suddenly get lots of queries
> from many wallets who don't need an update, so my solution is that the
> blockchain server caches a tree of prefixes which are published to
> clients. Then they can make a query.
>
> The thing I like about this model is that fetch_history is
> deterministic, has no state and then I can focus on optimising one thing.

I like this, and the prefix thing is a good idea for privacy. A bloom
filter could give even better privacy, but might be a lot harder to
look up efficiently.

> if it's a small binary, then contrib/ or tools/ under libwallet could
> work. We can also make it work as a plugin for Obelisk too which would
> be cool.

The watcher will be one or more C++ classes, not a binary (maybe sx
could wrap it in a binary). I imagine an interface somewhat like this:

class watcher()
{
    watcher(obelisk::fullnode_interface& connection, watcher_listener& listener,
        watcher_state* saved_state=nullptr);

    watch_address(payment_address address, frequency);

    watcher_state save();

    uint64_t get_balance(payment_address address);
    output_info_list get_utxos(payment_address address);
};

Upon calling watch_address, the watcher will begin monitoring that
address, and will notify the listener if anything happens there. The
listener doesn't care *how* this happens, as long as it happens.
Whether the watcher talks to obelisk, starts up an SPV node, or does
something else entirely is irrelevant. If obelisk changes to a new
model, such as what you described, watcher clients wouldn't be
affected.

Basically, this class abstracts away all networking. The wallet
doesn't care about networking; it cares about addresses and the
balanaces available at those addresses. This class provides that
abstraction.

-William