taler-typescript-core

commit ae44f3187c0428ff9c84c881e194df9f1642d06b
parent 540cd68e6ef2d56559d91657ecde3b789a441119
Author: Florian Dold <dold@taler.net>
Date:   Thu,  6 Aug 2026 19:02:48 +0200

wallet: only store denominations that can still be withdrawn from

An exchange advertises a denomination until its legal expiration, so most of a
/keys response is denominations no wallet can ever withdraw from -- 952 of 1022
on the demo exchange.  Ones already in the database are kept regardless: a coin
in the wallet may refer to them.

Issue: https://bugs.taler.net/n/11334

Diffstat:
M
packages/taler-wallet-core/src/exchanges.ts
 | 
37
++++++++++++++++++++++++++++++++++++-

1 file changed, 36 insertions(+), 1 deletion(-)
diff --git a/packages/taler-wallet-core/src/exchanges.ts b/packages/taler-wallet-core/src/exchanges.ts
@@ -973,6 +973,22 @@ function denomFamilyParamsKey(p: WalletDenomFamilyParams): string {
 }
 
 /**
+ * Is a denomination we have not seen before worth a row in the database?
+ *
+ * Only denominations that can still be withdrawn from are: the wallet gets a
+ * coin of a denomination by withdrawing or refreshing into it, and both pick
+ * from the withdrawable ones.  A denomination it already has a row for is
+ * never dropped on this basis -- that row may be what a coin in the wallet
+ * refers to, and losing it would count the coin as vanished.
+ */
+function isDenomWorthStoring(d: DenominationInfo): boolean {
+  const expireWithdraw = AbsoluteTime.fromProtocolTimestamp(
+    d.stampExpireWithdraw,
+  );
+  return !AbsoluteTime.isExpired(expireWithdraw);
+}
+
+/**
  * Timestamp (in seconds) to ask the exchange to cherry-pick /keys by, or
  * undefined when the whole response should be downloaded.
  *
@@ -2181,7 +2197,21 @@ export async function updateExchangeFromUrlHandler(
       );
     }
 
+    let numDenomsSkipped = 0;
+
     for (const currentDenom of denomInfos) {
+      const oldDenom = oldDenomByDph.get(currentDenom.denomPubHash);
+
+      // A denomination that can no longer be withdrawn from is only of
+      // interest for coins we already hold, and we cannot hold a coin of one
+      // we never stored.  Exchanges keep advertising these for years after
+      // they stop issuing them -- on the demo exchange 952 of 1022 -- so not
+      // writing them is most of the cost of adding an exchange.
+      if (!oldDenom && !isDenomWorthStoring(currentDenom)) {
+        numDenomsSkipped++;
+        continue;
+      }
+
       const familyParams: WalletDenomFamilyParams = {
         exchangeBaseUrl: currentDenom.exchangeBaseUrl,
         exchangeMasterPub: currentDenom.exchangeMasterPub,
@@ -2251,7 +2281,6 @@ export async function updateExchangeFromUrlHandler(
         isLost: currentDenom.isLost,
       };
 
-      const oldDenom = oldDenomByDph.get(currentDenom.denomPubHash);
       if (oldDenom) {
         // FIXME: Do consistency check, report to auditor if necessary.
         // See https://bugs.taler.net/n/8594
@@ -2279,6 +2308,12 @@ export async function updateExchangeFromUrlHandler(
       }
     }
 
+    if (numDenomsSkipped > 0) {
+      logger.trace(
+        `did not store ${numDenomsSkipped} of ${denomInfos.length} denominations of ${exchangeBaseUrl}, no longer withdrawable`,
+      );
+    }
+
     // Update list issue date for all denominations,
     // and mark non-offered denominations as such.
     //