protocol: add MockClient and refactor VCR cassette file reading (#85)

* Move `VcrClient` to `@apibara/protocol` and rename to `MockClient`.
* Abstract cassette file reading to `loadCassette` function

packages/indexer/src/testing/setup.ts

@@ -2,9 +2,10 @@ import { test as viTest } from "vitest";
 import type { Indexer } from "../indexer";
 import {
   type CassetteOptions,
-  VcrClient,
   type VcrConfig,
   type VcrReplayResult,
+  isCassetteAvailable,
+  loadCassette,
   record,
   replay,
 } from "../vcr";
@@ -46,13 +47,9 @@ async function withClient<TFilter, TBlock, TRet>(
 
   const context: WithClientContext<TFilter, TBlock, TRet> = {
     async run(indexer) {
-      const client = new VcrClient(
-        vcrConfig,
-        cassetteName,
-        indexer.streamConfig,
-      );
+      const client = loadCassette<TFilter, TBlock>(vcrConfig, cassetteName);
 
-      if (!client.isCassetteAvailable()) {
+      if (!isCassetteAvailable(vcrConfig, cassetteName)) {
         await record(vcrConfig, client, indexer, cassetteOptions);
       }
 

packages/indexer/src/vcr/helper.ts

@@ -1,3 +1,7 @@
+import fs from "node:fs";
+import path from "node:path";
+import type { VcrConfig } from "./config";
+
 export function deserialize(str: string) {
   return JSON.parse(str, (_, value) =>
     typeof value === "string" && value.match(/^\d+n$/)
@@ -13,3 +17,11 @@ export function serialize(obj: Record<string, unknown>): string {
     "\t",
   );
 }
+
+export function isCassetteAvailable(
+  vcrConfig: VcrConfig,
+  cassetteName: string,
+): boolean {
+  const filePath = path.join(vcrConfig.cassetteDir, `${cassetteName}.json`);
+  return fs.existsSync(filePath);
+}

packages/indexer/src/vcr/index.ts

@@ -1,4 +1,3 @@
-export * from "./client";
 export * from "./config";
 export * from "./helper";
 export * from "./record";

packages/indexer/src/vcr/replay.ts

@@ -1,15 +1,18 @@
-import { type Indexer, run } from "@apibara/indexer";
-import type { Cursor } from "@apibara/protocol";
+import fs from "node:fs";
+import path from "node:path";
+import type { Client, Cursor } from "@apibara/protocol";
+import { MockClient } from "@apibara/protocol/testing";
+import { type Indexer, run } from "../indexer";
 import { vcr } from "../testing/vcr";
-import { VcrClient } from "./client";
+import { type CassetteDataType, deserialize } from "../vcr";
 import type { VcrConfig } from "./config";
 
 export async function replay<TFilter, TBlock, TRet>(
   vcrConfig: VcrConfig,
   indexer: Indexer<TFilter, TBlock, TRet>,
   cassetteName: string,
 ): Promise<VcrReplayResult<TRet>> {
-  const client = new VcrClient(vcrConfig, cassetteName, indexer.streamConfig);
+  const client = loadCassette<TFilter, TBlock>(vcrConfig, cassetteName);
 
   const sink = vcr<TRet>();
 
@@ -23,3 +26,17 @@ export async function replay<TFilter, TBlock, TRet>(
 export type VcrReplayResult<TRet> = {
   outputs: Array<{ endCursor?: Cursor; data: TRet[] }>;
 };
+
+export function loadCassette<TFilter, TBlock>(
+  vcrConfig: VcrConfig,
+  cassetteName: string,
+): Client<TFilter, TBlock> {
+  const filePath = path.join(vcrConfig.cassetteDir, `${cassetteName}.json`);
+
+  const data = fs.readFileSync(filePath, "utf8");
+  const cassetteData: CassetteDataType<TFilter, TBlock> = deserialize(data);
+
+  const { filter, messages } = cassetteData;
+
+  return new MockClient(messages, [filter]);
+}

packages/protocol/package.json

@@ -4,7 +4,10 @@
   "type": "module",
   "source": "./src/index.ts",
   "main": "./src/index.ts",
-  "exports": "./src/index.ts",
+  "exports": {
+    ".": "./src/index.ts",
+    "./testing": "./src/testing/index.ts"
+  },
   "publishConfig": {
     "files": ["dist", "src", "README.md"],
     "main": "./dist/index.mjs",
@@ -14,6 +17,11 @@
         "types": "./dist/index.d.ts",
         "import": "./dist/index.mjs",
         "default": "./dist/index.mjs"
+      },
+      "./testing": {
+        "types": "./dist/testing/index.d.ts",
+        "import": "./dist/testing/index.mjs",
+        "default": "./dist/testing/index.mjs"
       }
     }
   },

packages/protocol/src/testing/client.ts

@@ -0,0 +1,49 @@
+import assert from "node:assert";
+
+import type { Client, ClientCallOptions, StreamDataOptions } from "../client";
+import type { StatusRequest, StatusResponse } from "../status";
+import type { StreamDataRequest, StreamDataResponse } from "../stream";
+
+export class MockClient<TFilter, TBlock> implements Client<TFilter, TBlock> {
+  constructor(
+    private messages: StreamDataResponse<TBlock>[],
+    private filter: TFilter[],
+  ) {}
+
+  async status(
+    request?: StatusRequest,
+    options?: ClientCallOptions,
+  ): Promise<StatusResponse> {
+    throw new Error("Client.status is not implemented for VcrClient");
+  }
+
+  streamData(request: StreamDataRequest<TFilter>, options?: StreamDataOptions) {
+    assert.deepStrictEqual(
+      this.filter,
+      request.filter,
+      "Request and Cassette filter mismatch",
+    );
+
+    return new StreamDataIterable(this.messages);
+  }
+}
+
+export class StreamDataIterable<TBlock> {
+  constructor(private messages: StreamDataResponse<TBlock>[]) {}
+
+  [Symbol.asyncIterator](): AsyncIterator<StreamDataResponse<TBlock>> {
+    let index = 0;
+    const messages = this.messages;
+
+    return {
+      async next() {
+        if (index >= messages.length) {
+          return { done: true, value: undefined };
+        }
+
+        const message = messages[index++];
+        return { done: false, value: message };
+      },
+    };
+  }
+}

packages/protocol/src/testing/index.ts

@@ -0,0 +1 @@
+export * from "./client";