feat(plugin-keychain-memory): add observability via RxJS ReplaySubjects

1. This is an example of how to add observability to a plugin such as
if you had to somehow expose the stream of transaction execution requests
flowing through a connector plugin but did not feel like setting up Kafka
or RabbitMQ just for this and instead opted to do it with an in-process,
purely NodeJS/Javascript based solution.
2. The downside of this is of course that this doesn't work well in a
distributed computing environment just by itself, since if you were to
host a fleet of servers running the same connector plugin with horizontal
scaling, then this wouldn't be able to observe all the invocations across
the server fleet, but it would still make it easier to implement a functionality
like that.
3. The main purpose of this pull request is educational. The keychain memory
plugin is only used for testing and demonstration purposes and I wanted to
show to a few other contributors what I meant when I was explaining that
they could just use RxJS subjects to allow consumers of the connector plugins
to observe the stream of transactions flowing through said connector plugin
instance.

Signed-off-by: Peter Somogyvari <peter.somogyvari@accenture.com>

packages/cactus-plugin-keychain-memory/package.json

@@ -64,6 +64,7 @@
     "axios": "1.6.0",
     "express": "4.19.2",
     "prom-client": "13.2.0",
+    "rxjs": "7.8.1",
     "uuid": "9.0.1"
   },
   "devDependencies": {

packages/cactus-plugin-keychain-memory/src/main/typescript/plugin-keychain-memory.ts

@@ -26,12 +26,15 @@ import { HasKeychainEntryV1Endpoint } from "./web-services/has-keychain-entry-en
 import { DefaultService } from "./generated/crpc/services/default_service_connect";
 import { KeychainMemoryCrpcSvcOpenApi } from "./crpc-services/keychain-memory-crpc-svc-openapi";
 import { ServiceType } from "@bufbuild/protobuf";
+import { Observable, ReplaySubject, Subject } from "rxjs";
 
 export interface IPluginKeychainMemoryOptions extends ICactusPluginOptions {
   logLevel?: LogLevelDesc;
   backend?: Map<string, string>;
   keychainId: string;
   prometheusExporter?: PrometheusExporter;
+  readonly observabilityBufferSize?: number;
+  readonly observabilityTtlSeconds?: number;
 }
 
 export class PluginKeychainMemory
@@ -42,6 +45,22 @@ export class PluginKeychainMemory
   private readonly backend: Map<string, string>;
   private readonly log: Logger;
   private readonly instanceId: string;
+  private readonly observabilityBufferSize: number;
+  private readonly observabilityTtlSeconds: number;
+
+  private readonly getSubject: Subject<{
+    readonly key: string;
+    readonly value: string;
+  }>;
+  private readonly setSubject: Subject<{
+    readonly key: string;
+    readonly value: string;
+  }>;
+  private readonly hasSubject: Subject<{
+    readonly key: string;
+    readonly isPresent: boolean;
+  }>;
+  private readonly deleteSubject: Subject<{ readonly key: string }>;
   private endpoints: IWebServiceEndpoint[] | undefined;
   public prometheusExporter: PrometheusExporter;
 
@@ -56,13 +75,19 @@ export class PluginKeychainMemory
     Checks.truthy(opts.instanceId, `${fnTag} options.instanceId`);
     Checks.nonBlankString(opts.keychainId, `${fnTag} options.keychainId`);
 
+    this.observabilityBufferSize = opts.observabilityBufferSize || 1;
+    this.observabilityTtlSeconds = opts.observabilityTtlSeconds || 1;
+
     this.backend = opts.backend || new Map();
     Checks.truthy(this.backend, `${fnTag} arg options.backend`);
 
     const level = this.opts.logLevel || "INFO";
     const label = this.className;
     this.log = LoggerProvider.getOrCreate({ level, label });
 
+    this.log.debug("observabilityBufferSize=%o", this.observabilityBufferSize);
+    this.log.debug("observabilityTtlSeconds=%o", this.observabilityTtlSeconds);
+
     this.instanceId = this.opts.instanceId;
     this.prometheusExporter =
       opts.prometheusExporter ||
@@ -78,6 +103,23 @@ export class PluginKeychainMemory
       `Never use ${this.className} in production. ` +
         `It does not support encryption. It stores everything in plain text.`,
     );
+
+    this.getSubject = new ReplaySubject(
+      this.observabilityBufferSize,
+      this.observabilityTtlSeconds,
+    );
+    this.setSubject = new ReplaySubject(
+      this.observabilityBufferSize,
+      this.observabilityTtlSeconds,
+    );
+    this.hasSubject = new ReplaySubject(
+      this.observabilityBufferSize,
+      this.observabilityTtlSeconds,
+    );
+    this.deleteSubject = new ReplaySubject(
+      this.observabilityBufferSize,
+      this.observabilityTtlSeconds,
+    );
   }
 
   public getOpenApiSpec(): unknown {
@@ -181,23 +223,52 @@ export class PluginKeychainMemory
   async get(key: string): Promise<string> {
     const value = this.backend.get(key);
     if (value) {
+      this.getSubject.next({ key, value });
       return value;
     } else {
       throw new Error(`Keychain entry for "${key}" not found.`);
     }
   }
 
+  public observeGet(): Observable<{ readonly key: string }> {
+    return this.getSubject.asObservable();
+  }
+
   async has(key: string): Promise<boolean> {
-    return this.backend.has(key);
+    const isPresent = this.backend.has(key);
+    this.hasSubject.next({ key, isPresent });
+    return isPresent;
+  }
+
+  public observeHas(): Observable<{
+    readonly key: string;
+    readonly isPresent: boolean;
+  }> {
+    return this.hasSubject.asObservable();
   }
 
   async set(key: string, value: string): Promise<void> {
     this.backend.set(key, value);
+    this.setSubject.next({ key, value });
     this.prometheusExporter.setTotalKeyCounter(this.backend.size);
   }
 
+  public observeSet(): Observable<{
+    readonly key: string;
+    readonly value: string;
+  }> {
+    return this.setSubject.asObservable();
+  }
+
   async delete(key: string): Promise<void> {
     this.backend.delete(key);
+    this.deleteSubject.next({ key });
     this.prometheusExporter.setTotalKeyCounter(this.backend.size);
   }
+
+  public observeDelete(): Observable<{
+    readonly key: string;
+  }> {
+    return this.deleteSubject.asObservable();
+  }
 }

packages/cactus-plugin-keychain-memory/src/test/typescript/unit/plugin-keychain-memory-observability.test.ts

@@ -0,0 +1,84 @@
+import "jest-extended";
+import { v4 as uuidV4 } from "uuid";
+
+import { LogLevelDesc, LoggerProvider } from "@hyperledger/cactus-common";
+
+import { PluginKeychainMemory } from "../../../main/typescript/public-api";
+
+const logLevel: LogLevelDesc = "INFO";
+
+describe("PluginKeychainMemory", () => {
+  const log = LoggerProvider.getOrCreate({
+    label: "plugin-keychain-memory-observability.test.ts",
+    level: logLevel,
+  });
+
+  test("can observe set operations", async () => {
+    const keychain = new PluginKeychainMemory({
+      instanceId: uuidV4(),
+      keychainId: uuidV4(),
+      logLevel,
+    });
+
+    let getCount = 0;
+    const stratedAt = new Date();
+
+    const taskPromise = new Promise<void>((resolve) => {
+      keychain.observeSet().subscribe({
+        next: (value) => {
+          getCount++;
+          log.debug("NEXT_SET: startedAt=%o value=%o", stratedAt, value);
+          if (getCount >= 5) {
+            resolve();
+          }
+        },
+      });
+
+      keychain.set("some-key-that-does-not-matter-1", uuidV4());
+      keychain.set("some-key-that-does-not-matter-2", uuidV4());
+      keychain.set("some-key-that-does-not-matter-3", uuidV4());
+      keychain.set("some-key-that-does-not-matter-4", uuidV4());
+      keychain.set("some-key-that-does-not-matter-5", uuidV4());
+    });
+    await expect(taskPromise).toResolve();
+  }, 500);
+
+  test("can observe set operations with buffer", async () => {
+    const keychain = new PluginKeychainMemory({
+      instanceId: uuidV4(),
+      keychainId: uuidV4(),
+      logLevel,
+      observabilityBufferSize: 5,
+      observabilityTtlSeconds: 1000,
+    });
+
+    let getCount = 0;
+    const stratedAt = new Date();
+
+    keychain.set("some-key-that-does-not-matter-1", uuidV4());
+    keychain.set("some-key-that-does-not-matter-2", uuidV4());
+    keychain.set("some-key-that-does-not-matter-3", uuidV4());
+    keychain.set("some-key-that-does-not-matter-4", uuidV4());
+    keychain.set("some-key-that-does-not-matter-5", uuidV4());
+
+    const taskPromise = new Promise<void>((resolve) => {
+      keychain.observeSet().subscribe({
+        next: (value) => {
+          getCount++;
+          log.debug("NEXT_SET_1: startedAt=%o value=%o", stratedAt, value);
+        },
+      });
+      keychain.observeSet().subscribe({
+        next: (value) => {
+          getCount++;
+          log.debug("NEXT_SET_2: startedAt=%o value=%o", stratedAt, value);
+          if (getCount >= 10) {
+            resolve();
+          }
+        },
+      });
+    });
+
+    await expect(taskPromise).toResolve();
+  }, 500);
+});

yarn.lock

@@ -8457,6 +8457,7 @@ __metadata:
     express: "npm:4.19.2"
     npm-run-all2: "npm:6.1.2"
     prom-client: "npm:13.2.0"
+    rxjs: "npm:7.8.1"
     uuid: "npm:9.0.1"
   languageName: unknown
   linkType: soft