1 files changed, 98 insertions, 0 deletions
diff --git a/packages/taler-util/src/observability.ts b/packages/taler-util/src/observability.ts
new file mode 100644
index 000000000..0171142c8
--- /dev/null
+++ b/packages/taler-util/src/observability.ts
@@ -0,0 +1,98 @@
+/*
+ This file is part of GNU Taler
+ (C) 2024 Taler Systems S.A.
+
+ 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.
+
+ GNU 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 {
+  AbsoluteTime,
+  CancellationToken,
+  ObservabilityEvent,
+} from "./index.js";
+import {
+  HttpRequestLibrary,
+  HttpRequestOptions,
+  HttpResponse,
+} from "./http-common.js";
+import { ObservabilityEventType } from "./notifications.js";
+import { getErrorDetailFromException } from "./errors.js";
+
+/**
+ * Observability sink can be passed into various operations (HTTP requests, DB access)
+ * to do structured logging within a particular context (task, request, ...).
+ */
+export interface ObservabilityContext {
+  observe(evt: ObservabilityEvent): void;
+}
+
+let seqId = 1000;
+
+export class ObservableHttpClientLibrary implements HttpRequestLibrary {
+  private readonly cancelatorById = new Map<string, CancellationToken.Source>();
+  constructor(
+    private impl: HttpRequestLibrary,
+    private oc: ObservabilityContext,
+  ) {}
+
+  public cancelRequest(id: string): void {
+    const cancelator = this.cancelatorById.get(id);
+    if (!cancelator) return;
+    cancelator.cancel();
+  }
+
+  async fetch(
+    url: string,
+    opt?: HttpRequestOptions | undefined,
+  ): Promise<HttpResponse> {
+    const id = `req-${seqId}`;
+    seqId = seqId + 1;
+
+    const cancelator = CancellationToken.create();
+    if (opt?.cancellationToken) {
+      opt.cancellationToken.onCancelled(cancelator.cancel);
+    }
+    this.cancelatorById.set(id, cancelator);
+
+    this.oc.observe({
+      id,
+      when: AbsoluteTime.now(),
+      type: ObservabilityEventType.HttpFetchStart,
+      url: url,
+    });
+
+    const optsWithCancel = opt ?? {};
+    optsWithCancel.cancellationToken = cancelator.token;
+    try {
+      const res = await this.impl.fetch(url, optsWithCancel);
+      this.oc.observe({
+        id,
+        when: AbsoluteTime.now(),
+        type: ObservabilityEventType.HttpFetchFinishSuccess,
+        url,
+        status: res.status,
+      });
+      return res;
+    } catch (e) {
+      this.oc.observe({
+        id,
+        when: AbsoluteTime.now(),
+        type: ObservabilityEventType.HttpFetchFinishError,
+        url,
+        error: getErrorDetailFromException(e),
+      });
+      throw e;
+    } finally {
+      this.cancelatorById.delete(id);
+    }
+  }
+}