Re: [Taler] Pointing taler-exchange to my libeufin nexus / sandbox setup

[Christian Grothoff]

Hi Florian,

Answers inline below...

On 11/15/22 02:33, Florian Jung via Taler wrote:
> Hey everyone,
>
> By now, I have setup with libeufin-sandbox and libeufin-nexus. I have an 
> ebics connection and have imported the sandboxed bank account to my nexus:
>
> libeufin-cli connections import-bank-account --offered-account-id 
> jrluser --nexus-bank-account-id myconn_jrluser myconn
>
> taler and anastasis facades are set up (even though I don't understand 
> what the latter is for. Can you explain?)

That's for anastasis.lu authorization via bank-wire-transfer, you don't 
need the Anastasis facade at this point.

> The nexus has a superuser (god / supersecret) and a normal user (myuser 
> / mypass).
>
>
> What I now don't understand is how to proceed: How do I setup my 
> exchange to use that bank account? In detail, what config options are 
> required and how does the payto uri need to look like: Is
>
> [exchange-account-1]
> PAYTO_URI = "payto://iban/AB123456" # output of `libeufin cli accounts 
> show`
> WIRE_GATEWAY_URL = http://nexus-host:5017/ # same as LIBEUFIN_NEXUS_URL. 
> Or do i need trailing paths?
>
> WIRE_GATEWAY_AUTH_METHOD = basic
> USERNAME = myuser
> PASSWORD = mypass
>
> correct?

I think the wire_gateway_url may be wrong, I think you need to put a 
suffix there, usually looks more like:
    $LIBEUFIN_NEXUS_URL/facades/$NAME/taler-wire-gateway/

If you manually run 'taler-exchange-wirewatch' (or look at the logs) and 
the tool is "happy" talking to the bank, then it should be correct ;-).

> Does it only allow to "load" taler wallets by wiring money *into* this 
> AB123456 account? Or can we already "pay out" money by wiring money 
> *from* this account to an user-specified account (destroying their Talers)?

Both: run taler-exchange-wirewatch to monitor money coming in, and 
taler-exchange-aggregator/closer/transfer to "pay out".

> I guess in the real world, this would be equivalent to the exchange's 
> account at a higher-level bank (possibly the central bank), correct?

Yes.

> And how does this account interact with the Taler Cashier app? IIUC, the 
> Cashier can transfer money from one taler wallet to another. So do I 
> assume correctly that I need to fake a sandbox transaction into the 
> AB123456 account, so the exchange believes that the cashier's wallet has 
> been loaded with *lots of money*?

Yes, you should create a third (cashier/user) account on libeufin 
sandbox, then wire money from the admin/master/central bank account to 
that third account, effectively creating digital cash as a liability of 
the central bank (and bootstrapping your economy with the cashier 
account being the first to get money).  Then you can point the Taler 
Cashier app to that third account (give it your username/password).

> Or can I configure the exchange / the libeufin sandbox (which?) such 
> that the cashier's account may go into debt?

You can also enable going into debt, but the "natural" setup we use is
for (only) the admin/central bank account to go negative. Then the
admin/central bank account's negative balance represents the total money
in the system, and the exchange (positive) balance represents the Taler 
coins in circulation.

> My goal is to handle the payment of drinks and food at a (hacker) event 
> over Taler; there would be a (human-operated) place where you can swap 
> money into taler, and then you can pay it.

Great. Let us know if you manage and where, I'm sure we'd like to 
promote the event :-)

> It would be very handy if that "cashier account" would just go into 
> debt, so that in the end, we can check that the amount of physical money 
> in the box equals the negative account balance. Can it work that way?

It can work this way. Not allowing debts is a nice way to limit liabilities,
but if you don't need that, just allow negative balances and it'll be 
fine, too.
> Thank you for all the help so far, and I hope I can contribute back by 
> improving the manual a bit more :).

That would be great ;-).

Happy hacking!

-Christian