From fb3da3a28d6ed6a16ca7d0fa8ec775de51c7df6b Mon Sep 17 00:00:00 2001
From: Florian Dold <florian@dold.me>
Date: Thu, 11 Mar 2021 13:08:41 +0100
Subject: towards recovering from accidental double spends

---
 packages/taler-wallet-core/src/operations/pay.ts | 44 ++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

(limited to 'packages/taler-wallet-core/src/operations/pay.ts')

diff --git a/packages/taler-wallet-core/src/operations/pay.ts b/packages/taler-wallet-core/src/operations/pay.ts
index 03bf9e119..3add9bbbf 100644
--- a/packages/taler-wallet-core/src/operations/pay.ts
+++ b/packages/taler-wallet-core/src/operations/pay.ts
@@ -84,6 +84,8 @@ import {
   throwUnexpectedRequestError,
   getHttpResponseErrorDetails,
   readSuccessResponseJsonOrErrorCode,
+  HttpResponseStatus,
+  readTalerErrorResponse,
 } from "../util/http";
 import { TalerErrorCode } from "../TalerErrorCode";
 import { URL } from "../util/url";
@@ -1001,6 +1003,22 @@ async function storePayReplaySuccess(
   });
 }
 
+/**
+ * Handle a 409 Conflict response from the merchant.
+ *
+ * We do this by going through the coin history provided by the exchange and
+ * (1) verifying the signatures from the exchange
+ * (2) adjusting the remaining coin value
+ * (3) re-do coin selection.
+ */
+async function handleInsufficientFunds(
+  ws: InternalWalletState,
+  proposalId: string,
+  err: TalerErrorDetails,
+): Promise<void> {
+  throw Error("payment re-denomination not implemented yet");
+}
+
 /**
  * Submit a payment to the merchant.
  *
@@ -1078,6 +1096,32 @@ async function submitPay(
       };
     }
 
+    if (resp.status === HttpResponseStatus.Conflict) {
+      const err = await readTalerErrorResponse(resp);
+      if (
+        err.code ===
+        TalerErrorCode.MERCHANT_POST_ORDERS_ID_PAY_INSUFFICIENT_FUNDS
+      ) {
+        // Do this in the background, as it might take some time
+        handleInsufficientFunds(ws, proposalId, err).catch(async (e) => {
+          await incrementProposalRetry(ws, proposalId, {
+            code: TalerErrorCode.WALLET_UNEXPECTED_EXCEPTION,
+            message: "unexpected exception",
+            hint: "unexpected exception",
+            details: {
+              exception: e,
+            },
+          });
+        });
+
+        return {
+          type: ConfirmPayResultType.Pending,
+          // FIXME: should we return something better here?
+          lastError: err,
+        };
+      }
+    }
+
     const merchantResp = await readSuccessResponseJsonOrThrow(
       resp,
       codecForMerchantPayResponse(),
-- 
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