From: Luke Dashjr <luke@dashjr.org>
To: Tim Ruffing <tim.ruffing@mmci.uni-saarland.de>
Date: Mon, 6 Mar 2017 22:14:47 +0000
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Message-Id: <201703062214.47660.luke@dashjr.org>
Cc: bitcoin-dev@lists.linuxfoundation.org
Subject: Re: [bitcoin-dev] Currency/exchange rate information API
Precedence: list

On Monday, March 06, 2017 9:54:16 PM Tim Ruffing wrote:
> Having the rate at the time of payment is indeed very useful, yes.
> However that requires just a single value per payment, and there is no
> query that tells the server "give me the value closest to timestamp t"
> or similar.
> Of course the client can download and keep a large part of history and
> extract the information on its own but I can imagine that not every
> clients wants to do that, and also the client does not know in advance
> the bounds (from, to) that it must query.

It would be a privacy leak to request only the specific timestamps, but I 
suppose many wallets lack even basic privacy to begin with.

To address the bounds issue, I have specified that when from/to don't have an 
exact record, that the previous/next (respectively) is provided.

Hopefully this addresses both concerns?

> In the current draft the client or the server cannot specify
> granularity. If the clients only wants one value per day but for an
> entire year, then it has to perform many requests or download and
> process a very large response.

That's what the "timedelta" field solves, no?
If you want one value per day, you'd put 86400.

> Also, I think it's okay that the type field allows for arbitrary user-
> defined values, but it should also have some precisely defined values
> (e.g. the mentioned low/high/open/close/typical).
> For example, it's not clear currently what "low" means for a timestamp
> (as opposed to a time span). Is it the low of the entire day or the low
> since the previous record or something different?

Is it not sufficient for the server to specify this in the description of the 
given currency-pair feed?

Luke