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Diffstat (limited to 'design-documents/036-currency-conversion-service.rst')
| -rw-r--r-- | design-documents/036-currency-conversion-service.rst | 107 |
1 files changed, 48 insertions, 59 deletions
diff --git a/design-documents/036-currency-conversion-service.rst b/design-documents/036-currency-conversion-service.rst index 319896bb..92d88499 100644 --- a/design-documents/036-currency-conversion-service.rst +++ b/design-documents/036-currency-conversion-service.rst @@ -1,5 +1,5 @@ -DD 36: Currency conversion service. -################################### +DD 36: Currency conversion service +################################## Summary ======= @@ -35,74 +35,63 @@ currency. Requirements ============ -* CCS must not impact the Nexus structure. +* CCS must not impact the libeufin-nexus structure. * CCS must trigger Taler withdrawls every time a customer buys the - regional currency ('buy-in' operation). + regional currency ('cash-in' operation). * CCS must offer cash-out operations. -* CCS should react as soon as possible to buy-in and cash-out operations. +* CCS should react as soon as possible to cash-in and cash-out operations. * CCS must show its state to administrators and offer management tools. * CCS must link every fiat-side of a cash-out to its regional currency counterpart. In particular, because every cash-out starts with a payment *P* from regio-user to regio-issuer and ends with another - payment *Q* from fiat-issuer to fiat-target, CCS must link P and Q. + payment *Q* from fiat-issuer to fiat-target, CCS must link P and Q. Proposed Solution ================= -The following design assumes that CCS is coded into libeufin Sandbox. +The following design assumes that CCS is coded in libeufin-bank and that +libeufin-bank and libeufin-nexus share the same database with separate +schemas. The solution relies on SQL triggers to atomically synchronise +cash-in and cash-out operations between the two schemas. + +SQL triggers and conversion operations +-------------------------------------- + +Libeufin-bank controls the conversion support and sets up or removes +conversion SQL triggers when necessary. In order for the SQL triggers to +perform the conversion operations, the configurable rates/fees are stored +in the database and the conversion operations are performed using stored +SQL procedures. The SQL triggers and conversion procedures are stored in +the libeufin-bank schema. Cash-out operation ------------------ -The libeufin Sandbox component learns instantly about a cash-out -operation, because it's *the* service offering such feature. -Therefore, as soon as a cash-out operation gets TAN-confirmed, -Sandbox performs a first wire transfer from regio-user to regio-issuer -by specifying the amount without any rates/fees applied. Along -the same database transaction, Sandbox stores the *instructions* -of another payment *P* from fiat-issuer to fiat-target, but this time -**with** the cash-out rates/fees. Notably, P includes the **current** -fiat-target and the rates/fees, since these are configurable. - -Asynchronously, a background task picks P and sends it to the fiat bank. -Finally, fiat bank conducts P and fiat-target receives the wanted -amount. The same background task should also retry previous payments -like P that failed to be submitted to fiat bank. - -CCS offers management endpoints for prepared fiat-transactions. -Through them, adminisrators can see, retry, or cancel every fiat-transaction -that was prepared to pay fiat-target. - -Buy-in operation ----------------- - -A buy-in operation starts as soon as the customer sends a fiat -payment from fiat-customer to fiat-issuer. Sandbox is responsible to -detect such an incoming payment in a timely fashion. The detection -happens by long polling on the Nexus JSON API. Nexus is ultimately -responsible to query the fiat bank via EBICS every X seconds. X -should match the tightest interval allowed by the bank. - -When Sandbox detects one incoming payment on fiat-issuer, it applies the -**current** buy-in rates/fees and wires the resuling amount from regio-issuer -to regio-exchange. At this point, Nexus detects the incoming payment on -regio-exchange and makes the exchange aware via the Taler Wire Gateway API. -From now on, the system proceeds like it always did in Taler. - -Milestones to a MVP -=================== - -* Refactor configuration in Sandbox: `7527 <https://bugs.gnunet.org/view.php?id=7527>`_, `7515 <https://bugs.gnunet.org/view.php?id=7515>`_. -* Make rates/fees and TAN channels configurable in Sandbox: `7694 <https://bugs.gnunet.org/view.php?id=7694>`_. -* Long polling in Nexus to serve TWG: `6987 <https://bugs.gnunet.org/view.php?id=6987>`_, `6383 <https://bugs.gnunet.org/view.php?id=6383>`_. -* Long polling in Nexus to serve fiat-transactions via native API: `7693 <https://bugs.gnunet.org/view.php?id=7693>`_. -* Long polling in Sandbox to ask Nexus fiat-transactions via native API. -* Serve transactions with date ranges in Sandbox Access API: `7685 <https://bugs.gnunet.org/view.php?id=7685>`_ -* Implement JSON-based "bank connection" in Nexus. That's how Nexus - gets regio-transactions to serve in the TWG. -* Implement fiat-bank's EBICS flavor. -* Ask transactions with date ranges in such flavor in Nexus: `7686 <https://bugs.gnunet.org/view.php?id=7686>`_. -* Implement fiat-transactions management tools. - -.. note:: - The list can be incomplete and not necessarily ordered. +Libeufin-bank learns instantly about a cash-out operation, because it's +*the* service offering such feature. Therefore, as soon as a cash-out +operation gets TAN-confirmed, libeufin-bank performs a wire transfer from +regio-user to regio-issuer by specifying the amount without any rates/fees +applied. Along the same database transaction, a SQL trigger store the +*instructions* of another payment *P* from fiat-issuer to fiat-target, +but this time **with** the cash-out rates/fees. + +Asynchronously, a libeufin-nexus background task picks P and sends it to +the fiat bank. Finally, fiat bank conducts P and fiat-target receives the +wanted amount. The same libeufin-nexus background task should also retry +previous payments like P that failed to be submitted to fiat bank. + +Cash-in operation +----------------- + +A cashin-in operation starts as soon as the customer sends a fiat +payment from fiat-customer to fiat-issuer. + +The libeufin-nexus component is responsible to query the fiat bank +via EBICS every X seconds. X should match the tightest interval allowed +by the bank. + +When libeufin-nexus registers an incoming payment on fiat-issuer in the +database, a SQL trigger applies the **current** cash-in rates/fees and +performs a wire transfer from regio-issuer to regio-exchange. Libeufin-bank +makes the exchange aware via the Taler Wire Gateway API and from now on, +the system proceeds like it always did in Taler. |