[Taler] Why the 2 fractional digits limit in the sandbox?

[Florian Jung]

Hi,

while trying to reproduce the issue that throws an invalid EBICS error 
when transferring 1µEUR in the sandbox (the smallest possible amount 
seemed to be 10µEUR due to a 5 fractional digits limit in the XML 
parser), I found out that recent versions of the sandbox only allow 2 
fractional digits (i.e. whole eurocents, no fractional cents any more).

The change was introduced with f5995b846492c7b091c09e204f7c6450b5369034.


I found a comment saying:

+                    /**
+                     * NOTE: this check breaks the compatibility with 
pain.001,
+                     * because that allows up to 5 fractional digits.  
For Taler
+                     * compatibility however, we enforce the max 2 
fractional digits policy.
+                     */


While this explains to me why I was unable to transfer 1µEUR (the 
sandbox wrongfully created a statement with that amount, which then 
rightfully was rejected as invalid), I don't understand why we are now 
limiting the amounts to 2 fractional digits only.

In my tests, no part of the setup broke when I used amounts with 5 
fractional digits.


Ideally, the allowed fractional digits could be configured, because I 
see use cases where only 2 digits are allowed (anything that mimics a 
"real" bank which probably only allows whole eurocents) and cases where 
lots of digits are allowed (e.g. for our WICMP setup, we used the full 5 
digit range for microtransactions).


On the other hand: Would it be possible for the *exchange* to support 
coins in smaller fractions, while the sandbox / bank supports payouts 
only whole cents? That would allow us to have microtransactions at least 
in the Taler world (which would be enough. nobody wants to pay a sepa 
fee for a 0.1 eurocent transfer :D)


Cheers,

Florian