[miniflare] Fix Buffer type not accepted for D1 blob bindings (#12514)

Co-authored-by: devin-ai-integration[bot] <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Author: ascorbic

.changeset/fix-buffer-devalue.md

@@ -0,0 +1,13 @@
+---
+"miniflare": patch
+---
+
+fix: normalise typed array subclasses in devalue serialization
+
+Node.js `Buffer` extends `Uint8Array` but isn't available in all runtimes. When
+a `Buffer` was passed through the proxy serialization bridge (e.g. as a D1 bind
+parameter via `getPlatformProxy()`), the reviver would fail because `"Buffer"`
+isn't in the allowed constructor list and may not exist on `globalThis` in workerd.
+
+The reducer now normalises subclass constructor names to the nearest standard
+typed array parent before serialization, matching structured clone behaviour.

packages/miniflare/src/workers/core/devalue.ts

@@ -52,12 +52,26 @@ export const structuredSerializableReducers: ReducersRevivers = {
 	},
 	ArrayBufferView(value) {
 		if (ArrayBuffer.isView(value)) {
-			return [
-				value.constructor.name,
-				value.buffer,
-				value.byteOffset,
-				value.byteLength,
-			];
+			let name = value.constructor.name;
+			// Subclasses like Node.js `Buffer` extend standard typed arrays but
+			// aren't available in all runtimes. Normalise to the parent constructor.
+			if (
+				!ALLOWED_ARRAY_BUFFER_VIEW_CONSTRUCTORS.some((c) => c.name === name)
+			) {
+				for (const ctor of ALLOWED_ARRAY_BUFFER_VIEW_CONSTRUCTORS) {
+					if (value instanceof ctor) {
+						name = ctor.name;
+						break;
+					}
+				}
+			}
+			let buf = value.buffer;
+			let off = value.byteOffset;
+			if (off !== 0 || buf.byteLength !== value.byteLength) {
+				buf = buf.slice(off, off + value.byteLength);
+				off = 0;
+			}
+			return [name, buf, off, value.byteLength];
 		}
 	},
 	RegExp(value) {

packages/miniflare/test/workers/core/serialize.spec.ts

@@ -1,3 +1,4 @@
+import { Buffer } from "node:buffer";
 import { parse, stringify } from "devalue";
 import {
 	createHTTPReducers,
@@ -8,6 +9,19 @@ import {
 import { test } from "vitest";
 import { NODE_PLATFORM_IMPL } from "../../../src/plugins/core/proxy/types";
 
+test("serialize Buffer as Uint8Array", ({ expect }) => {
+	const input = Buffer.from([99, 88, 77]);
+
+	const serialized = stringify(input, structuredSerializableReducers);
+	const deserialized = parse(serialized, structuredSerializableRevivers);
+
+	// Buffer should round-trip as Uint8Array since Buffer isn't available in all runtimes
+	expect(deserialized).toBeInstanceOf(Uint8Array);
+	expect(new Uint8Array(deserialized as ArrayBuffer)).toEqual(
+		new Uint8Array([99, 88, 77])
+	);
+});
+
 test("serialize RegExp object consisting of only ascii chars", ({ expect }) => {
 	const input = new RegExp(/HelloWorld/);