ZIP: Specify Payment API

[daira]

Placeholder. See https://zcash.slack.com/archives/paymentapi/p1468977244000002 for a discussion about how to represent amounts. (To do: that archive is not public, copy the relevant parts.)

[nathan-at-least]

Related is how to manage proving parameters: zcash/zcash#432 (comment)

Tangential topics for SPV clients: #288 delegated JoinSplit detection and #1113 delegated proving.

[nathan-at-least]

Unresolved issue: How do we represent values in the API? We want lossless representation, but we also are dealing with Bitcoin's API which may use "float-ish" numbers. Something to review and make an explicit decision on.

[zookozcash]

Re "floatish", the problem is that if we send or accept decimals in the
API, then a lot of programmers will use floats/doubles to produce or
consume those numbers, which will lead to bugs.

It's entirely possible to use a proper decimal datatype instead of
floats/doubles in all modern languages, so a potential mitigation is just
to add documentation saying "do NOT ever use floats/doubles to store or
process this. There is a library in your language that handles decimals. Go
find out and use it and nothing but it to handle these numbers."

Here's a simple example of the problems with using floats for decimals: 0.1

• 0.1 != 0.01

Not only is 0.1 times 0.1 not exactly 0.01, it isn't even the closest
possible number to 0.01.

https://web.archive.org/web/20140723054136/https://zooko.com/uri/URI:DIR2-MDMF-RO:dwvqalbdt4ax4vgupcewxljg3u:bej7hhojmpuugy77oyydmazf6uu7huiipkctih7adky7e6txavnq/klog.html#pyutil.jsonutil

On Jul 20, 2016 10:52 AM, "Nathan Wilcox" notifications@github.com wrote:

Unresolved issue: How do we represent values in the API? We want lossless
representation, but we also are dealing with Bitcoin's API which may use
"float-ish" numbers. Something to review and make an explicit decision on.

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[ebfull]

Hm, is the payment API in scope for the specification?

[daira]

I'm deciding that it is not in scope for the specification, but should be maintained as a ZIP. Can someone convert https://github.com/zcash/zcash/blob/master/doc/payment-api.md to rST and submit it please?