2 files changed, 150 insertions, 0 deletions
diff --git a/packages/taler-util/src/RequestThrottler.ts b/packages/taler-util/src/RequestThrottler.ts
new file mode 100644
index 000000000..7689b4215
--- /dev/null
+++ b/packages/taler-util/src/RequestThrottler.ts
@@ -0,0 +1,149 @@
+/*
+ This file is part of GNU Taler
+ (C) 2019 GNUnet e.V.
+
+ GNU 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
+ GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+import { Logger } from "./logging.js";
+import { getTimestampNow, timestampCmp, timestampDifference } from "./time.js";
+
+/**
+ * Implementation of token bucket throttling.
+ */
+
+
+const logger = new Logger("RequestThrottler.ts");
+
+/**
+ * Maximum request per second, per origin.
+ */
+const MAX_PER_SECOND = 100;
+
+/**
+ * Maximum request per minute, per origin.
+ */
+const MAX_PER_MINUTE = 500;
+
+/**
+ * Maximum request per hour, per origin.
+ */
+const MAX_PER_HOUR = 2000;
+
+/**
+ * Throttling state for one origin.
+ */
+class OriginState {
+  tokensSecond: number = MAX_PER_SECOND;
+  tokensMinute: number = MAX_PER_MINUTE;
+  tokensHour: number = MAX_PER_HOUR;
+  private lastUpdate = getTimestampNow();
+
+  private refill(): void {
+    const now = getTimestampNow();
+    if (timestampCmp(now, this.lastUpdate) < 0) {
+      // Did the system time change?
+      this.lastUpdate = now;
+      return;
+    }
+    const d = timestampDifference(now, this.lastUpdate);
+    if (d.d_ms === "forever") {
+      throw Error("assertion failed");
+    }
+    this.tokensSecond = Math.min(
+      MAX_PER_SECOND,
+      this.tokensSecond + d.d_ms / 1000,
+    );
+    this.tokensMinute = Math.min(
+      MAX_PER_MINUTE,
+      this.tokensMinute + d.d_ms / 1000 / 60,
+    );
+    this.tokensHour = Math.min(
+      MAX_PER_HOUR,
+      this.tokensHour + d.d_ms / 1000 / 60 / 60,
+    );
+    this.lastUpdate = now;
+  }
+
+  /**
+   * Return true if the request for this origin should be throttled.
+   * Otherwise, take a token out of the respective buckets.
+   */
+  applyThrottle(): boolean {
+    this.refill();
+    if (this.tokensSecond < 1) {
+      logger.warn("request throttled (per second limit exceeded)");
+      return true;
+    }
+    if (this.tokensMinute < 1) {
+      logger.warn("request throttled (per minute limit exceeded)");
+      return true;
+    }
+    if (this.tokensHour < 1) {
+      logger.warn("request throttled (per hour limit exceeded)");
+      return true;
+    }
+    this.tokensSecond--;
+    this.tokensMinute--;
+    this.tokensHour--;
+    return false;
+  }
+}
+
+/**
+ * Request throttler, used as a "last layer of defense" when some
+ * other part of the re-try logic is broken and we're sending too
+ * many requests to the same exchange/bank/merchant.
+ */
+export class RequestThrottler {
+  private perOriginInfo: { [origin: string]: OriginState } = {};
+
+  /**
+   * Get the throttling state for an origin, or
+   * initialize if no state is associated with the
+   * origin yet.
+   */
+  private getState(origin: string): OriginState {
+    const s = this.perOriginInfo[origin];
+    if (s) {
+      return s;
+    }
+    const ns = (this.perOriginInfo[origin] = new OriginState());
+    return ns;
+  }
+
+  /**
+   * Apply throttling to a request.
+   *
+   * @returns whether the request should be throttled.
+   */
+  applyThrottle(requestUrl: string): boolean {
+    const origin = new URL(requestUrl).origin;
+    return this.getState(origin).applyThrottle();
+  }
+
+  /**
+   * Get the throttle statistics for a particular URL.
+   */
+  getThrottleStats(requestUrl: string): Record<string, unknown> {
+    const origin = new URL(requestUrl).origin;
+    const state = this.getState(origin);
+    return {
+      tokensHour: state.tokensHour,
+      tokensMinute: state.tokensMinute,
+      tokensSecond: state.tokensSecond,
+      maxTokensHour: MAX_PER_HOUR,
+      maxTokensMinute: MAX_PER_MINUTE,
+      maxTokensSecond: MAX_PER_SECOND,
+    };
+  }
+}
diff --git a/packages/taler-util/src/index.ts b/packages/taler-util/src/index.ts
index 0141be13b..573b4a5c7 100644
--- a/packages/taler-util/src/index.ts
+++ b/packages/taler-util/src/index.ts
@@ -30,3 +30,4 @@ export {
   secretbox_open,
   crypto_sign_keyPair_fromSeed,
 } from "./nacl-fast.js";
+export { RequestThrottler } from "./RequestThrottler.js";