cachedAsyncBuffer tests

package.json

@@ -27,25 +27,25 @@
     "test": "vitest run"
   },
   "devDependencies": {
-    "@rollup/plugin-commonjs": "28.0.0",
+    "@rollup/plugin-commonjs": "28.0.1",
     "@rollup/plugin-node-resolve": "15.3.0",
     "@rollup/plugin-replace": "6.0.1",
     "@rollup/plugin-terser": "0.4.4",
-    "@rollup/plugin-typescript": "12.1.0",
+    "@rollup/plugin-typescript": "12.1.1",
     "@types/node": "22.7.5",
     "@types/react": "18.3.11",
-    "@types/react-dom": "18.3.0",
-    "@vitest/coverage-v8": "2.1.2",
+    "@types/react-dom": "18.3.1",
+    "@vitest/coverage-v8": "2.1.3",
     "eslint": "9.12.0",
-    "eslint-plugin-jsdoc": "50.3.1",
-    "hightable": "0.5.2",
+    "eslint-plugin-jsdoc": "50.4.1",
+    "hightable": "0.5.3",
     "http-server": "14.1.1",
     "hyparquet-compressors": "0.1.4",
     "react": "18.3.1",
     "react-dom": "18.3.1",
     "rollup": "4.24.0",
-    "typescript": "5.6.2",
-    "typescript-eslint": "8.8.1",
-    "vitest": "2.1.2"
+    "typescript": "5.6.3",
+    "typescript-eslint": "8.9.0",
+    "vitest": "2.1.3"
   }
 }

test/asyncbuffer.test.js

@@ -0,0 +1,43 @@
+import { describe, expect, it, vi } from 'vitest'
+import { cachedAsyncBuffer } from '../src/asyncBuffer.js'
+
+describe('cachedAsyncBuffer', () => {
+  it('caches slices of a file to avoid multiple reads', async () => {
+    const slice = vi.fn(async (start, end) => {
+      // Simulate an async slice operation
+      if (end === undefined) end = 1000
+      if (start < 0) start = Math.max(0, 1000 + start)
+      const buffer = new ArrayBuffer(end - start)
+      return buffer
+    })
+    const cachedFile = cachedAsyncBuffer({
+      byteLength: 1000,
+      slice,
+    })
+
+    // Test cache miss
+    const slice1 = await cachedFile.slice(0, 100)
+    expect(slice).toHaveBeenCalledTimes(1)
+    expect(slice1.byteLength).toBe(100)
+
+    // Test cache hit for the same range
+    const slice2 = await cachedFile.slice(0, 100)
+    expect(slice).toHaveBeenCalledTimes(1) // No additional call
+    expect(slice2).toBe(slice1) // Exact same object from cache
+
+    // Test cache with undefined end, should use byteLength as end
+    const slice3 = await cachedFile.slice(900)
+    expect(slice).toHaveBeenCalledTimes(2)
+    expect(slice3.byteLength).toBe(100)
+
+    // Test cache hit for suffix-range
+    const slice4 = await cachedFile.slice(-100)
+    expect(slice).toHaveBeenCalledTimes(2) // Still no additional call
+    expect(slice4).toBe(slice3) // Cached result reused
+
+    // Verify that asking for the same end implicitly gets from cache
+    const slice5 = await cachedFile.slice(900, 1000)
+    expect(slice).toHaveBeenCalledTimes(2) // Still no additional call
+    expect(slice5).toBe(slice3) // Cached result reused
+  })
+})