Bank transaction idempotency

12 files changed, 171 insertions, 41 deletions

diff --git a/API_CHANGES.md b/API_CHANGES.md
index 3440e24f..da085bb7 100644
--- a/API_CHANGES.md
+++ b/API_CHANGES.md
@@ -4,16 +4,24 @@ This files contains all the API changes for the current release:
 
 ## bank serve
 
-- POST /accounts: now returns RegisterAccountResponse with IBAN on http code 200 instead of 201
-- CREATE /accounts: new debit_threshold field similar to the one of PATH /accounts
-- GET /config: new default_debit_threshold field for the default debt limit for newly created accounts
-- GET /config: new supported_tan_channels field which lists all the TAN channels supported by the server
-- GET /config: new allow_edit_name and allow_edit_cashout_payto_uri fields for path authorisation
-- POST /accounts: rename challenge_contact_data to contact_data and internal_payto_uri to payto_uri
-- PATCH /accounts/USERNAME: add is_public, remove is_taler_exchange and rename challenge_contact_data to contact_data
+- POST /accounts: now returns RegisterAccountResponse with IBAN on http code 200
+  instead of 201
+- CREATE /accounts: new debit_threshold field similar to the one of PATH
+  /accounts
+- GET /config: new default_debit_threshold field for the default debt limit for
+  newly created accounts
+- GET /config: new supported_tan_channels field which lists all the TAN channels
+  supported by the server
+- GET /config: new allow_edit_name and allow_edit_cashout_payto_uri fields for
+  path authorisation
+- POST /accounts: rename challenge_contact_data to contact_data and
+  internal_payto_uri to payto_uri
+- PATCH /accounts/USERNAME: add is_public, remove is_taler_exchange and rename
+  challenge_contact_data to contact_data
 - GET /accounts: add payto_uri, is_public and is_taler_exchange
 - GET /accounts/USERNAME: add is_public and is_taler_exchange
-- GET /public-accounts: add is_taler_exchange and rename account_name to username
+- GET /public-accounts: add is_taler_exchange and rename account_name to
+  username
 - PATCH /accounts: fix PATCH semantic
 - PATCH /accounts: restrict PATCH contact_data to admin
 - POST /accounts/USERNAME/transactions: prohibit transaction to admin account
@@ -25,7 +33,8 @@ This files contains all the API changes for the current release:
 - Add POST /accounts/USERNAME/challenge/CHALLENGE_ID
 - Add POST /accounts/USERNAME/challenge/CHALLENGE_ID/confirm
 - POST /accounts/USERNAME/cashouts: remove tan_channel field
-- POST /accounts/USERNAME/cashouts/CASHOUT_ID: remove confirmation_time, tan_channel, tan_info and status fields
+- POST /accounts/USERNAME/cashouts/CASHOUT_ID: remove confirmation_time,
+  tan_channel, tan_info and status fields
 - POST /accounts/$USERNAME/cashouts: remove status field
 - POST /cashouts: remove status field
 - PATCH /accounts/USERNAME: add tan_channel
@@ -37,6 +46,7 @@ This files contains all the API changes for the current release:
 - GET /accounts: add row_id field
 - GET /public-accounts: add row_id field
 - GET /config: new bank_name field for the bank name
+- POST /accounts/USERNAME/transactions: new request_uid field for idempotency and new idempotency error
 
 ## bank cli
 
diff --git a/bank/src/main/kotlin/tech/libeufin/bank/Constants.kt b/bank/src/main/kotlin/tech/libeufin/bank/Constants.kt
index 48fc3992..7a192308 100644
--- a/bank/src/main/kotlin/tech/libeufin/bank/Constants.kt
+++ b/bank/src/main/kotlin/tech/libeufin/bank/Constants.kt
@@ -40,7 +40,7 @@ const val IBAN_ALLOCATION_RETRY_COUNTER: Int = 5
 const val MAX_BODY_LENGTH: Long = 4 * 1024 // 4kB
 
 // API version  
-const val COREBANK_API_VERSION: String = "4:3:0"
+const val COREBANK_API_VERSION: String = "4:4:0"
 const val CONVERSION_API_VERSION: String = "0:0:0"
 const val INTEGRATION_API_VERSION: String = "2:0:2"
 const val WIRE_GATEWAY_API_VERSION: String = "0:2:0"
diff --git a/bank/src/main/kotlin/tech/libeufin/bank/TalerMessage.kt b/bank/src/main/kotlin/tech/libeufin/bank/TalerMessage.kt
index 0284266b..ce459baa 100644
--- a/bank/src/main/kotlin/tech/libeufin/bank/TalerMessage.kt
+++ b/bank/src/main/kotlin/tech/libeufin/bank/TalerMessage.kt
@@ -380,7 +380,8 @@ data class AccountData(
 @Serializable
 data class TransactionCreateRequest(
     val payto_uri: Payto,
-    val amount: TalerAmount?
+    val amount: TalerAmount?,
+    val request_uid: ShortHashCode?
 )
 
 @Serializable
diff --git a/bank/src/main/kotlin/tech/libeufin/bank/api/CoreBankApi.kt b/bank/src/main/kotlin/tech/libeufin/bank/api/CoreBankApi.kt
index dd6aab4b..a3bb8265 100644
--- a/bank/src/main/kotlin/tech/libeufin/bank/api/CoreBankApi.kt
+++ b/bank/src/main/kotlin/tech/libeufin/bank/api/CoreBankApi.kt
@@ -459,6 +459,7 @@ private fun Routing.coreBankTransactionsApi(db: Database, ctx: BankConfig) {
                 subject = subject,
                 amount = amount,
                 timestamp = Instant.now(),
+                requestUid = req.request_uid,
                 is2fa = challenge != null
             )
             when (res) {
@@ -479,6 +480,10 @@ private fun Routing.coreBankTransactionsApi(db: Database, ctx: BankConfig) {
                     "Insufficient funds",
                     TalerErrorCode.BANK_UNALLOWED_DEBIT
                 )
+                BankTransactionResult.RequestUidReuse -> throw conflict(
+                    "request_uid used already",
+                    TalerErrorCode.BANK_TRANSFER_REQUEST_UID_REUSED
+                )
                 is BankTransactionResult.Success -> call.respond(TransactionCreateResponse(res.id))
             }
         }
diff --git a/bank/src/main/kotlin/tech/libeufin/bank/db/AccountDAO.kt b/bank/src/main/kotlin/tech/libeufin/bank/db/AccountDAO.kt
index 13bc1e09..f78947e7 100644
--- a/bank/src/main/kotlin/tech/libeufin/bank/db/AccountDAO.kt
+++ b/bank/src/main/kotlin/tech/libeufin/bank/db/AccountDAO.kt
@@ -157,7 +157,7 @@ class AccountDAO(private val db: Database) {
                 if (bonus.value != 0L || bonus.frac != 0) {
                     conn.prepareStatement("""
                         SELECT out_balance_insufficient
-                        FROM bank_transaction(?,'admin','bonus',(?,?)::taler_amount,?,true)
+                        FROM bank_transaction(?,'admin','bonus',(?,?)::taler_amount,?,true,NULL)
                     """).run {
                         setString(1, internalPayto.canonical)
                         setLong(2, bonus.value)
diff --git a/bank/src/main/kotlin/tech/libeufin/bank/db/TransactionDAO.kt b/bank/src/main/kotlin/tech/libeufin/bank/db/TransactionDAO.kt
index 9b03cd2d..81fd558f 100644
--- a/bank/src/main/kotlin/tech/libeufin/bank/db/TransactionDAO.kt
+++ b/bank/src/main/kotlin/tech/libeufin/bank/db/TransactionDAO.kt
@@ -38,6 +38,7 @@ class TransactionDAO(private val db: Database) {
         data object BothPartySame: BankTransactionResult
         data object BalanceInsufficient: BankTransactionResult
         data object TanRequired: BankTransactionResult
+        data object RequestUidReuse: BankTransactionResult
     }
 
     /** Create a new transaction */
@@ -47,7 +48,8 @@ class TransactionDAO(private val db: Database) {
         subject: String,
         amount: TalerAmount,
         timestamp: Instant,
-        is2fa: Boolean
+        is2fa: Boolean,
+        requestUid: ShortHashCode?,
     ): BankTransactionResult = db.serializable { conn ->
         val now = timestamp.toDbMicros() ?: throw faultyTimestampByBank()
         conn.transaction {
@@ -57,6 +59,7 @@ class TransactionDAO(private val db: Database) {
                     ,out_debtor_not_found
                     ,out_same_account
                     ,out_balance_insufficient
+                    ,out_request_uid_reuse
                     ,out_tan_required
                     ,out_credit_bank_account_id
                     ,out_debit_bank_account_id
@@ -65,7 +68,8 @@ class TransactionDAO(private val db: Database) {
                     ,out_creditor_is_exchange 
                     ,out_debtor_is_exchange
                     ,out_creditor_admin
-                FROM bank_transaction(?,?,?,(?,?)::taler_amount,?,?)
+                    ,out_idempotent
+                FROM bank_transaction(?,?,?,(?,?)::taler_amount,?,?,?)
             """
             )
             stmt.setString(1, creditAccountPayto.canonical)
@@ -75,6 +79,7 @@ class TransactionDAO(private val db: Database) {
             stmt.setInt(5, amount.frac)
             stmt.setLong(6, now)
             stmt.setBoolean(7, is2fa)
+            stmt.setBytes(8, requestUid?.raw)
             stmt.executeQuery().use {
                 when {
                     !it.next() -> throw internalServerError("Bank transaction didn't properly return")
@@ -83,6 +88,8 @@ class TransactionDAO(private val db: Database) {
                     it.getBoolean("out_same_account") -> BankTransactionResult.BothPartySame
                     it.getBoolean("out_balance_insufficient") -> BankTransactionResult.BalanceInsufficient
                     it.getBoolean("out_creditor_admin") -> BankTransactionResult.AdminCreditor
+                    it.getBoolean("out_request_uid_reuse") -> BankTransactionResult.RequestUidReuse
+                    it.getBoolean("out_idempotent") -> BankTransactionResult.Success(it.getLong("out_debit_row_id"))
                     it.getBoolean("out_tan_required") -> BankTransactionResult.TanRequired
                     else -> {
                         val creditAccountId = it.getLong("out_credit_bank_account_id")
diff --git a/bank/src/test/kotlin/AmountTest.kt b/bank/src/test/kotlin/AmountTest.kt
index 94716208..ccd64400 100644
--- a/bank/src/test/kotlin/AmountTest.kt
+++ b/bank/src/test/kotlin/AmountTest.kt
@@ -53,7 +53,8 @@ class AmountTest {
                 subject = "test",
                 amount = due,
                 timestamp = Instant.now(),
-                is2fa = false
+                is2fa = false,
+                requestUid = null
             )
             val txBool = when (txRes) {
                 BankTransactionResult.BalanceInsufficient -> false
diff --git a/bank/src/test/kotlin/CoreBankApiTest.kt b/bank/src/test/kotlin/CoreBankApiTest.kt
index f5f668f5..b1b89cc9 100644
--- a/bank/src/test/kotlin/CoreBankApiTest.kt
+++ b/bank/src/test/kotlin/CoreBankApiTest.kt
@@ -174,7 +174,9 @@ class CoreBankAccountsApiTest {
             // Check idempotency
             client.post("/accounts") {
                 json(req)
-            }.assertOk()
+            }.assertOkJson<RegisterAccountResponse> {
+                assertEquals(payto, it.internal_payto_uri)
+            }
             // Check idempotency with payto
             client.post("/accounts") {
                 json(req) {
@@ -208,8 +210,9 @@ class CoreBankAccountsApiTest {
         // Testing idempotency
         client.post("/accounts") {
             json(req)
-        }.assertOk()
-
+        }.assertOkJson<RegisterAccountResponse> {
+            assertEquals(payto.full("Jane"), it.internal_payto_uri)
+        }
         // Check admin only debit_threshold
         obj {
             "username" to "bat"
@@ -851,6 +854,28 @@ class CoreBankTransactionsApiTest {
                 assertEquals(TalerAmount("KUDOS:0.3"), tx.amount)
             }
         }
+
+        // Check idempotency
+        ShortHashCode.rand().let { requestUid ->
+            val id = client.postA("/accounts/merchant/transactions") {
+                json(valid_req) {
+                    "request_uid" to requestUid
+                }
+            }.assertOkJson<TransactionCreateResponse>().row_id
+            client.postA("/accounts/merchant/transactions") {
+                json(valid_req) {
+                    "request_uid" to requestUid
+                }
+            }.assertOkJson<TransactionCreateResponse> {
+                assertEquals(id, it.row_id)
+            }
+            client.postA("/accounts/merchant/transactions") {
+                json(valid_req) {
+                    "request_uid" to requestUid
+                    "amount" to "KUDOS:42"
+                }
+            }.assertConflict(TalerErrorCode.BANK_TRANSFER_REQUEST_UID_REUSED)
+        }
         
         // Check amount in payto_uri
         client.postA("/accounts/merchant/transactions") {
@@ -975,6 +1000,31 @@ class CoreBankTransactionsApiTest {
             assertBalance("merchant", "+KUDOS:2")
             assertBalance("customer", "+KUDOS:1")
         }
+
+        // Check 2fa idempotency
+        val req = obj {
+            "payto_uri" to "$customerPayto?message=tan+check&amount=KUDOS:1"
+            "request_uid" to ShortHashCode.rand()
+        }
+        val id = client.postA("/accounts/merchant/transactions") {
+            json(req)
+        }.assertChallenge { _,_->
+            assertBalance("merchant", "+KUDOS:2")
+            assertBalance("customer", "+KUDOS:1")
+        }.assertOkJson <TransactionCreateResponse> { 
+            assertBalance("merchant", "+KUDOS:1")
+            assertBalance("customer", "+KUDOS:2")
+        }.row_id
+        client.postA("/accounts/merchant/transactions") {
+            json(req)
+        }.assertOkJson<TransactionCreateResponse> {
+            assertEquals(id, it.row_id)
+        }
+        client.postA("/accounts/merchant/transactions") {
+            json(req) {
+                "payto_uri" to "$customerPayto?message=tan+chec2k&amount=KUDOS:1"
+            }
+        }.assertConflict(TalerErrorCode.BANK_TRANSFER_REQUEST_UID_REUSED)
     }
 }
 
@@ -1122,7 +1172,6 @@ class CoreBankWithdrawalApiTest {
     }
 }
 
-
 class CoreBankCashoutApiTest {
     // POST /accounts/{USERNAME}/cashouts
     @Test
@@ -1143,9 +1192,16 @@ class CoreBankCashoutApiTest {
         fillCashoutInfo("customer")
 
         // Check OK
+        val id = client.postA("/accounts/customer/cashouts") {
+            json(req) 
+        }.assertOkJson<CashoutResponse>().cashout_id
+
+        // Check idempotent
         client.postA("/accounts/customer/cashouts") {
             json(req) 
-        }.assertOkJson<CashoutResponse>()
+        }.assertOkJson<CashoutResponse> {
+            assertEquals(id, it.cashout_id)
+        }
 
         // Trigger conflict due to reused request_uid
         client.postA("/accounts/customer/cashouts") {
diff --git a/database-versioning/libeufin-bank-0001.sql b/database-versioning/libeufin-bank-0001.sql
index 334ddebe..a3ac4083 100644
--- a/database-versioning/libeufin-bank-0001.sql
+++ b/database-versioning/libeufin-bank-0001.sql
@@ -55,7 +55,7 @@ CREATE TYPE rounding_mode
 
 -- start of: bank accounts
 
-CREATE TABLE IF NOT EXISTS customers
+CREATE TABLE customers
   (customer_id INT8 GENERATED BY DEFAULT AS IDENTITY UNIQUE
   ,login TEXT NOT NULL UNIQUE
   ,password_hash TEXT NOT NULL
@@ -69,7 +69,7 @@ COMMENT ON COLUMN customers.cashout_payto
 COMMENT ON COLUMN customers.name
   IS 'Full name of the customer.';
 
-CREATE TABLE IF NOT EXISTS bank_accounts 
+CREATE TABLE bank_accounts 
   (bank_account_id INT8 GENERATED BY DEFAULT AS IDENTITY UNIQUE
   ,internal_payto_uri TEXT NOT NULL UNIQUE
   ,owning_customer_id INT8 NOT NULL UNIQUE -- UNIQUE enforces 1-1 map with customers
@@ -96,7 +96,7 @@ can be publicly shared';
 COMMENT ON COLUMN bank_accounts.owning_customer_id
   IS 'Login that owns the bank account';
 
-CREATE TABLE IF NOT EXISTS bearer_tokens
+CREATE TABLE bearer_tokens
   (bearer_token_id INT8 GENERATED BY DEFAULT AS IDENTITY UNIQUE
   ,content BYTEA NOT NULL UNIQUE CHECK (LENGTH(content)=32)
   ,creation_time INT8
@@ -114,7 +114,7 @@ COMMENT ON COLUMN bearer_tokens.bank_customer
      ' created the very first token that originated all the refreshes until'
      ' this token was created.';
 
-CREATE TABLE IF NOT EXISTS iban_history 
+CREATE TABLE iban_history 
   (iban TEXT PRIMARY KEY
   ,creation_time INT8 NOT NULL
   );
@@ -124,7 +124,7 @@ COMMENT ON TABLE iban_history IS 'Track all generated iban, some might be unused
 
 -- start of: money transactions
 
-CREATE TABLE IF NOT EXISTS bank_account_transactions 
+CREATE TABLE bank_account_transactions 
   (bank_transaction_id INT8 GENERATED BY DEFAULT AS IDENTITY UNIQUE
   ,creditor_payto_uri TEXT NOT NULL
   ,creditor_name TEXT NOT NULL
@@ -152,7 +152,7 @@ COMMENT ON COLUMN bank_account_transactions.bank_account_id
 -- end of: money transactions
 
 -- start of: TAN challenge
-CREATE TABLE IF NOT EXISTS challenges
+CREATE TABLE challenges
   (challenge_id INT8 GENERATED BY DEFAULT AS IDENTITY UNIQUE,
    code TEXT NOT NULL,
    creation_date INT8 NOT NULL,
@@ -179,7 +179,7 @@ COMMENT ON COLUMN challenges.confirmation_date
 
 -- start of: cashout management
 
-CREATE TABLE IF NOT EXISTS cashout_operations 
+CREATE TABLE cashout_operations 
   (cashout_id INT8 GENERATED BY DEFAULT AS IDENTITY UNIQUE
   ,request_uid BYTEA NOT NULL PRIMARY KEY CHECK (LENGTH(request_uid)=32)
   ,amount_debit taler_amount NOT NULL
@@ -207,7 +207,7 @@ COMMENT ON COLUMN cashout_operations.tan_info IS 'Info of the last successful tr
 -- end of: cashout management
 
 -- start of: Taler integration
-CREATE TABLE IF NOT EXISTS taler_exchange_outgoing
+CREATE TABLE taler_exchange_outgoing
   (exchange_outgoing_id INT8 GENERATED BY DEFAULT AS IDENTITY
   ,request_uid BYTEA UNIQUE CHECK (LENGTH(request_uid)=64)
   ,wtid BYTEA NOT NULL UNIQUE CHECK (LENGTH(wtid)=32)
@@ -219,7 +219,7 @@ CREATE TABLE IF NOT EXISTS taler_exchange_outgoing
     REFERENCES bank_accounts(bank_account_id)
   );
 
-CREATE TABLE IF NOT EXISTS taler_exchange_incoming
+CREATE TABLE taler_exchange_incoming
   (exchange_incoming_id INT8 GENERATED BY DEFAULT AS IDENTITY
   ,reserve_pub BYTEA NOT NULL UNIQUE CHECK (LENGTH(reserve_pub)=32)
   ,bank_transaction INT8 UNIQUE NOT NULL
@@ -227,7 +227,7 @@ CREATE TABLE IF NOT EXISTS taler_exchange_incoming
       ON DELETE CASCADE
   );
 
-CREATE TABLE IF NOT EXISTS taler_withdrawal_operations
+CREATE TABLE taler_withdrawal_operations
   (withdrawal_id INT8 GENERATED BY DEFAULT AS IDENTITY
   ,withdrawal_uuid uuid NOT NULL UNIQUE
   ,amount taler_amount NOT NULL
@@ -249,7 +249,7 @@ COMMENT ON COLUMN taler_withdrawal_operations.confirmation_done
 -- end of: Taler integration
 
 -- start of: Statistics
-CREATE TABLE IF NOT EXISTS bank_stats (
+CREATE TABLE bank_stats (
   timeframe stat_timeframe_enum NOT NULL
   ,start_time timestamp NOT NULL
   ,taler_in_count INT8 NOT NULL DEFAULT 0
@@ -295,7 +295,7 @@ COMMENT ON COLUMN bank_stats.cashout_fiat_volume
 
 -- start of: Conversion
 
-CREATE TABLE IF NOT EXISTS config (
+CREATE TABLE config (
   key TEXT NOT NULL PRIMARY KEY,
   value JSONB NOT NULL
 );
diff --git a/database-versioning/libeufin-bank-0003.sql b/database-versioning/libeufin-bank-0003.sql
new file mode 100644
index 00000000..14f1075f
--- /dev/null
+++ b/database-versioning/libeufin-bank-0003.sql
@@ -0,0 +1,28 @@
+--
+-- This file is part of TALER
+-- Copyright (C) 2024 Taler Systems SA
+--
+-- TALER is free software; you can redistribute it and/or modify it under the
+-- terms of the GNU General Public License as published by the Free Software
+-- Foundation; either version 3, or (at your option) any later version.
+--
+-- TALER is distributed in the hope that it will be useful, but WITHOUT ANY
+-- WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+-- A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+--
+-- You should have received a copy of the GNU General Public License along with
+-- TALER; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+
+BEGIN;
+
+SELECT _v.register_patch('libeufin-bank-0003', NULL, NULL);
+SET search_path TO libeufin_bank;
+
+CREATE TABLE bank_transaction_operations
+  (request_uid BYTEA UNIQUE CHECK (LENGTH(request_uid)=32)
+  ,bank_transaction INT8 UNIQUE NOT NULL
+    REFERENCES bank_account_transactions(bank_transaction_id)
+      ON DELETE CASCADE
+  );
+
+COMMIT;
diff --git a/database-versioning/libeufin-bank-drop.sql b/database-versioning/libeufin-bank-drop.sql
index 3746c28d..7fbcc342 100644
--- a/database-versioning/libeufin-bank-drop.sql
+++ b/database-versioning/libeufin-bank-drop.sql
@@ -5,6 +5,7 @@ BEGIN;
 -- legacy schema is being removed.
 SELECT _v.unregister_patch('libeufin-bank-0001');
 SELECT _v.unregister_patch('libeufin-bank-0002');
+SELECT _v.unregister_patch('libeufin-bank-0003');
 DROP SCHEMA libeufin_bank CASCADE;
 
 COMMIT;
diff --git a/database-versioning/libeufin-bank-procedures.sql b/database-versioning/libeufin-bank-procedures.sql
index 09680f23..8f82fc65 100644
--- a/database-versioning/libeufin-bank-procedures.sql
+++ b/database-versioning/libeufin-bank-procedures.sql
@@ -443,6 +443,7 @@ CREATE FUNCTION bank_transaction(
   IN in_amount taler_amount,
   IN in_timestamp INT8,
   IN in_is_tan BOOLEAN,
+  IN in_request_uid BYTEA,
   -- Error status
   OUT out_creditor_not_found BOOLEAN,
   OUT out_debtor_not_found BOOLEAN,
@@ -450,13 +451,15 @@ CREATE FUNCTION bank_transaction(
   OUT out_balance_insufficient BOOLEAN,
   OUT out_creditor_admin BOOLEAN,
   OUT out_tan_required BOOLEAN,
+  OUT out_request_uid_reuse BOOLEAN,
   -- Success return
   OUT out_credit_bank_account_id INT8,
   OUT out_debit_bank_account_id INT8,
   OUT out_credit_row_id INT8,
   OUT out_debit_row_id INT8,
   OUT out_creditor_is_exchange BOOLEAN,
-  OUT out_debtor_is_exchange BOOLEAN
+  OUT out_debtor_is_exchange BOOLEAN,
+  OUT out_idempotent BOOLEAN
 )
 LANGUAGE plpgsql AS $$
 BEGIN
@@ -466,24 +469,37 @@ SELECT bank_account_id, is_taler_exchange, login='admin'
   FROM bank_accounts
     JOIN customers ON customer_id=owning_customer_id
   WHERE internal_payto_uri = in_credit_account_payto;
-IF NOT FOUND THEN
-  out_creditor_not_found=TRUE;
-  RETURN;
-ELSIF out_creditor_admin THEN
+IF NOT FOUND OR out_creditor_admin THEN
+  out_creditor_not_found=NOT FOUND;
   RETURN;
 END IF;
--- Find debit bank account id and check it's a different account
+-- Find debit bank account ID and check it's a different account and if 2FA is required
 SELECT bank_account_id, is_taler_exchange, out_credit_bank_account_id=bank_account_id, NOT in_is_tan AND tan_channel IS NOT NULL
   INTO out_debit_bank_account_id, out_debtor_is_exchange, out_same_account, out_tan_required
   FROM bank_accounts 
     JOIN customers ON customer_id=owning_customer_id
   WHERE login = in_debit_account_username;
-IF NOT FOUND THEN
-  out_debtor_not_found=TRUE;
+IF NOT FOUND OR out_same_account THEN
+  out_debtor_not_found=NOT FOUND;
   RETURN;
-ELSIF out_same_account OR out_tan_required THEN
+END IF;
+-- Check for idempotence and conflict
+IF in_request_uid IS NOT NULL THEN
+  SELECT (amount != in_amount
+      OR subject != in_subject 
+      OR bank_account_id != out_debit_bank_account_id), bank_transaction
+    INTO out_request_uid_reuse, out_debit_row_id
+    FROM bank_transaction_operations
+      JOIN bank_account_transactions ON bank_transaction = bank_transaction_id
+    WHERE request_uid = in_request_uid;
+  IF found OR out_tan_required THEN
+    out_idempotent = found AND NOT out_request_uid_reuse;
+    RETURN;
+  END IF;
+ELSIF out_tan_required THEN
   RETURN;
 END IF;
+
 -- Perform bank transfer
 SELECT
   transfer.out_balance_insufficient,
@@ -503,6 +519,11 @@ SELECT
     NULL,
     NULL
   ) as transfer;
+-- Store operation
+IF in_request_uid IS NOT NULL THEN
+  INSERT INTO bank_transaction_operations (request_uid, bank_transaction)  
+    VALUES (in_request_uid, out_debit_row_id);
+END IF;
 END $$;
 COMMENT ON FUNCTION bank_transaction IS 'Create a bank transaction';