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From: Stephane Brossier <stephane@kill-bill.org>
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Date: Fri, 14 Feb 2014 12:28:24 -0800
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To: Kevin Greene <kgreenek@gmail.com>
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Cc: Pierre-Alexandre Meyer <pierre@kill-bill.org>,
	Bitcoin Dev <bitcoin-development@lists.sourceforge.net>
Subject: Re: [Bitcoin-development] Extension for BIP-0070 to support
	recurring payments
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Kevin,

We did a second iteration on the prototype to implement subscription =
cancellation and upgrade/downgrade. We checked in both the bitcoinj and =
php server to be able to test it.
We also worked on our side of the merchant implementation (Kill Bill) to =
feel confident that the protocol will support advanced business cases. =
At this point it is looking promising, but more work is needed to =
conclude.

We wanted to follow up on a few pervious points you raised:

> However, continuing to think about this even more, maybe the simple =
memo field along with an empty set of outputs is enough already.

=46rom our merchant side (Kill Bill), we do indeed use this field to =
report successes or errors. Maybe it would be useful to extend =
PaymentACK with a boolean success field (so the wallet doesn't commit =
the transaction in case of failures)?

> One high-level comment -- the wallet in this design doesn't have any =
way of knowing when the payments are supposed to end. I feel this is =
important to show to the user before they start their wallet polling =
infinitely.

We extended our RecurringPaymentDetails message to support this use =
case, as it solves the problem of subscription changes and cancellations =
for free.

We introduced the concept of a subscription, referred to by a unique id =
(the tuple merchant_id,subscription_id should be globally unique), which =
has multiple contracts (RecurringPaymentContract). Besides payment =
bounds, each contract has a validity period: generally, a subscription =
will have a unique active contract at a given time and potentially one =
or more pending ones.

For example, say you are on the gold plan (1 BTC/mo.) and want to =
downgrade to a bronze plan (0.5 BTC/mo.) at your next billing date. =
Wshen you click "Downgrade" on the merchant site, you will update your =
wallet with two contracts: the current valid one until your next billing =
date (for up to 1 BTC), and a pending one, starting at your next billing =
date (for up to 0.5 BTC/mo. and without an ending date).
Upon cancellation of the bronze plan, the end date of the contract will =
be updated and polling will stop eventually.

All of this contract metadata is returned to the wallet so the user can =
make an informed decision.


Thanks for your feedbacks!

S.


On Feb 11, 2014, at 10:37 PM, Kevin Greene <kgreenek@gmail.com> wrote:

> Sending this again and truncating since apparently the message body =
was too long.
>=20
> Thanks for humoring my questions!
>=20
> >I think reporting such errors to the wallet would make complete =
sense. However i am not clear why we would a separate url for that?
>=20
> Hmm, thinking about this more, adding a simple status_code in =
PaymentRequest would be a much easier way to achieve this. However, =
continuing to think about this even more, maybe the simple memo field =
along with an empty set of outputs is enough already.
>=20
> In bitcoinj, right now the code will throw a =
PaymentRequestException.InvalidOutputs exception if the set of outputs =
is empty with a message of "No Outputs". Because of that, there isn't a =
good way to tell the difference between a payment request that had no =
outputs and a payment request that had some invalid output(s).
>=20
> Question to everyone:
> How does bitcoin-qt handle a PaymentRequest with no outputs?


--Apple-Mail=_347698E4-F605-4008-8465-350BC552A927
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<html><head><meta http-equiv=3D"Content-Type" content=3D"text/html =
charset=3Diso-8859-1"></head><body style=3D"word-wrap: break-word; =
-webkit-nbsp-mode: space; -webkit-line-break: after-white-space; =
"><div>Kevin,</div><div><br></div><div>We did a second iteration on the =
prototype to implement subscription cancellation and upgrade/downgrade. =
We checked in both the bitcoinj and php server to be able to test =
it.</div><div>We also worked on our side of the merchant implementation =
(Kill Bill) to feel confident that the protocol will support advanced =
business cases. At this point it is looking promising, but more work is =
needed to conclude.</div><div><br></div><div>We wanted to follow up on a =
few pervious points you raised:</div><div><br></div><div><div>&gt; =
However, continuing to think about this even more, maybe the simple memo =
field along with an empty set of outputs is enough =
already.</div><div><br></div><div>=46rom our merchant side (Kill Bill), =
we do indeed use this field to report successes or errors. Maybe it =
would be useful to extend PaymentACK with a boolean success field (so =
the wallet doesn't commit the transaction in case of =
failures)?</div><div><br></div><div>&gt; One high-level comment -- the =
wallet in this design doesn't have any way of knowing when the payments =
are supposed to end. I feel this is important to show to the user before =
they start their wallet polling infinitely.</div><div><br></div><div>We =
extended our RecurringPaymentDetails message to support this use case, =
as it solves the problem of subscription changes and cancellations for =
free.</div><div><br></div><div>We introduced the concept of a =
subscription, referred to by a unique id (the tuple =
merchant_id,subscription_id should be globally unique), which has =
multiple contracts (RecurringPaymentContract). Besides payment bounds, =
each contract has a validity period: generally, a subscription will have =
a unique active contract at a given time and potentially one or more =
pending ones.</div><div><br></div><div>For example, say you are on the =
gold plan (1 BTC/mo.) and want to downgrade to a bronze plan (0.5 =
BTC/mo.) at your next billing date. Wshen you click "Downgrade" on the =
merchant site, you will update your wallet with two contracts: the =
current valid one until your next billing date (for up to 1 BTC), and a =
pending one, starting at your next billing date (for up to 0.5 BTC/mo. =
and without an ending date).</div><div>Upon cancellation of the bronze =
plan, the end date of the contract will be updated and polling will stop =
eventually.</div><div><br></div><div>All of this contract metadata is =
returned to the wallet so the user can make an informed =
decision.</div></div><div><br></div><div><br></div><div>Thanks for your =
feedbacks!</div><div><br></div><div>S.</div><div><br></div><div><br></div>=
<div><div>On Feb 11, 2014, at 10:37 PM, Kevin Greene &lt;<a =
href=3D"mailto:kgreenek@gmail.com">kgreenek@gmail.com</a>&gt; =
wrote:</div><br class=3D"Apple-interchange-newline"><blockquote =
type=3D"cite"><div dir=3D"ltr"><div class=3D"gmail_default" =
style=3D"color:rgb(51,102,102)">Sending this again and truncating since =
apparently the message body was too long.</div><div =
class=3D"gmail_default" style=3D"color:rgb(51,102,102)"><br></div>

<div class=3D"gmail_default" style=3D"color:rgb(51,102,102)"><div =
class=3D"gmail_default" =
style=3D"font-family:arial,sans-serif;font-size:13px">Thanks for =
humoring my questions!</div><div class=3D"im" =
style=3D"font-family:arial,sans-serif;font-size:13px">

<div class=3D"gmail_default" style=3D"color:rgb(51,102,102)"><span =
style=3D"color:rgb(34,34,34)"><br></span></div><div =
class=3D"gmail_default" style=3D"color:rgb(51,102,102)"><span =
style=3D"color:rgb(34,34,34)">&gt;I think reporting such errors to the =
wallet would make complete sense. However i am not clear why we would a =
separate url for that?</span><br>

</div><div class=3D"gmail_default" =
style=3D"color:rgb(51,102,102)"><br></div></div><div =
class=3D"gmail_default" =
style=3D"font-family:arial,sans-serif;font-size:13px">Hmm, thinking =
about this more, adding a simple status_code in PaymentRequest would be =
a much easier way to achieve this. However, continuing to think about =
this even more, maybe the simple memo field along with an empty set of =
outputs is enough already.</div>

<div class=3D"gmail_default" =
style=3D"font-family:arial,sans-serif;font-size:13px"><br></div><div =
class=3D"gmail_default" =
style=3D"font-family:arial,sans-serif;font-size:13px">In bitcoinj, right =
now the code will throw a PaymentRequestException.InvalidOutputs =
exception if the set of outputs is empty with a message of "No Outputs". =
Because of that, there isn't a good way to tell the difference between a =
payment request that had no outputs and a payment request that had some =
invalid output(s).</div>

<div class=3D"gmail_default" =
style=3D"font-family:arial,sans-serif;font-size:13px"><br></div><div =
class=3D"gmail_default" =
style=3D"font-family:arial,sans-serif;font-size:13px"><b>Question to =
everyone:</b></div><div class=3D"gmail_default" =
style=3D"font-family:arial,sans-serif;font-size:13px">

How does bitcoin-qt handle a PaymentRequest with no =
outputs?</div></div></div>
</blockquote></div><br></body></html>=

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