[hashcash] Re: hashcash stamp server

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On Wed, Mar 24, 2004 at 05:11:26PM +0000, Adam Back wrote:
>Kyle Hasselbacher wrote:
>> [...] I'd like to be able to tell it to generate tokens that expire in the 
>> future,
>> but that's not written yet. 

This is written now, BTW.  I'm hoping to take a last look at my new code
before releasing today.

>ie You could generate them with dates in the future but you should not
>use them when that date is still in the future.  [...]

That's the behavior I have.  I only take a premade stamp if the date
matches exactly.

>> * If I have an expensive pre-made token, it gets processed late even though
>>   it's really cheap.  I don't notice how cheap it is until the last minute.
>>   This means I could have messages that I can delivery immediately hanging
>>   around waiting for a message that I wasn't prepared for.
>
>could you get around this issue by checking whether pre-made stamps
>exist before generating stamps on demand?  Hmm but that's what you said
>above "When I go to generate a token, I first look to see if there's one
>already available at or above the postage required." so perhaps I am not
>understanding this scenario.

Here's what's going on...

* hashcash-sendmail computes a cost when the message is queued.  The cost
  centers around the time it takes to compute the stamp.

* hashcash-daemon uses those costs to determine work order.  Easy/cheap
  messages go first.

* When there's a premade token, that message turns out to be much easier
  than expected.

Taking premade stamps into account when computing the cost (at queue time)
is difficult because they can disappear between when the message is queued
and when it's picked up for delivery.  I could have hashcash-sendmail look
for premade tokens when it's doing its cost computation and somehow reserve
the tokens it finds.  That way a message it comes to think of as easy won't
get more expensive.  That'll work most of the time, but I could still see
it having odd effects.

For the moment I'm content to have it be simple and behave oddly.  I can
have it be complex and behave oddly later.
- -- 
Kyle Hasselbacher | Art is a lie which makes us realize the truth.
kyle@xxxxxxxxxxx  |                         -- Picasso
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