respect cache header

packages/taler-wallet-core/src/operations/exchanges.ts

@@ -43,16 +43,19 @@ import {
   WALLET_CACHE_BREAKER_CLIENT_VERSION,
   WALLET_EXCHANGE_PROTOCOL_VERSION,
 } from "./versions";
-import { getTimestampNow, Duration } from "../util/time";
+import { getTimestampNow, Duration, isTimestampExpired } from "../util/time";
 import { compare } from "../util/libtoolVersion";
 import { createRecoupGroup, processRecoupGroup } from "./recoup";
 import { TalerErrorCode } from "../TalerErrorCode";
 import {
   readSuccessResponseJsonOrThrow,
   readSuccessResponseTextOrThrow,
+  getExpiryTimestamp,
 } from "../util/http";
 import { Logger } from "../util/logging";
 import { URL } from "../util/url";
+import { reconcileReserveHistory } from "../util/reserveHistoryUtil";
+import { checkDbInvariant } from "../util/invariants";
 
 const logger = new Logger("exchanges.ts");
 
@@ -195,6 +198,7 @@ async function updateExchangeWithKeys(
         masterPublicKey: exchangeKeysJson.master_public_key,
         protocolVersion: protocolVersion,
         signingKeys: exchangeKeysJson.signkeys,
+        nextUpdateTime: getExpiryTimestamp(resp),
       };
       r.updateStatus = ExchangeUpdateStatus.FetchWire;
       r.lastError = undefined;
@@ -459,7 +463,7 @@ async function updateExchangeFromUrlImpl(
   const now = getTimestampNow();
   baseUrl = canonicalizeBaseUrl(baseUrl);
 
-  const r = await ws.db.get(Stores.exchanges, baseUrl);
+  let r = await ws.db.get(Stores.exchanges, baseUrl);
   if (!r) {
     const newExchangeRecord: ExchangeRecord = {
       builtIn: false,
@@ -476,7 +480,6 @@ async function updateExchangeFromUrlImpl(
       termsOfServiceAcceptedTimestamp: undefined,
       termsOfServiceLastEtag: undefined,
       termsOfServiceText: undefined,
-      updateDiff: undefined,
     };
     await ws.db.put(Stores.exchanges, newExchangeRecord);
   } else {
@@ -498,6 +501,16 @@ async function updateExchangeFromUrlImpl(
     });
   }
 
+  r = await ws.db.get(Stores.exchanges, baseUrl);
+  checkDbInvariant(!!r);
+
+
+  const t = r.details?.nextUpdateTime;
+  if (!forceNow && t && !isTimestampExpired(t)) {
+    logger.trace("using cached exchange info");
+    return r;
+  }
+
   await updateExchangeWithKeys(ws, baseUrl);
   await updateExchangeWithWireInfo(ws, baseUrl);
   await updateExchangeWithTermsOfService(ws, baseUrl);

packages/taler-wallet-core/src/types/dbTypes.ts

@@ -539,6 +539,11 @@ export interface ExchangeDetails {
    * Timestamp for last update.
    */
   lastUpdateTime: Timestamp;
+
+  /**
+   * When should we next update the information about the exchange?
+   */
+  nextUpdateTime: Timestamp;
 }
 
 export enum ExchangeUpdateStatus {

packages/taler-wallet-core/src/util/http.ts

@@ -26,7 +26,7 @@ import { Codec } from "./codec";
 import { OperationFailedError, makeErrorDetails } from "../operations/errors";
 import { TalerErrorCode } from "../TalerErrorCode";
 import { Logger } from "./logging";
-import { Duration } from "./time";
+import { Duration, Timestamp, getTimestampNow } from "./time";
 
 const logger = new Logger("http.ts");
 
@@ -253,3 +253,19 @@ export async function readSuccessResponseTextOrThrow<T>(
   }
   throwUnexpectedRequestError(httpResponse, r.talerErrorResponse);
 }
+
+/**
+ * Get the timestamp at which the response's content is considered expired.
+ */
+export function getExpiryTimestamp(httpResponse: HttpResponse): Timestamp {
+  const expiryDateMs = new Date(
+    httpResponse.headers.get("expiry") ?? "",
+  ).getTime();
+  if (Number.isNaN(expiryDateMs)) {
+    return getTimestampNow();
+  } else {
+    return {
+      t_ms: expiryDateMs,
+    }
+  }
+}

packages/taler-wallet-core/src/util/time.ts

@@ -46,6 +46,10 @@ export function getTimestampNow(): Timestamp {
   };
 }
 
+export function isTimestampExpired(t: Timestamp) {
+  return timestampCmp(t, getTimestampNow()) <= 0;
+}
+
 export function getDurationRemaining(
   deadline: Timestamp,
   now = getTimestampNow(),