构建可恢复上传服务

项目概述

本项目实现一个面向 large file upload 的完整系统，核心要解决的问题是 accepting chunked uploads that can resume after a network drop without re-sending completed chunks。整体由 Upload session、Chunk receiver、Offset tracker、Integrity checker、Completion assembler 五个模块组成，每个模块单一职责、可独立测试，最后通过集成测试验证端到端正确性。设计上把 a client that resumes at the wrong offset after a partial write and corrupts the assembled file 作为第一类需求先行处理，而非事后再补。

架构与关键决策

数据模型为 a session with a list of received chunk offsets and checksums, assembled into the final file only when every chunk is present。Upload session 定义其余阶段共同依赖的数据形状并在边界处校验输入；Chunk receiver 承载 large file upload 的正确性逻辑；Offset tracker 专门处理 a client that resumes at the wrong offset after a partial write and corrupts the assembled file，在失败路径上给出明确的拒绝、重试或降级策略；Integrity checker 提供可观测性，每次操作输出带关联 id 的结构化事件；Completion assembler 在过载时按既定方式降级，避免过载演变为数据损坏。配置与代码分离，使风险变更可经 diff 审阅。

实施与测试

按五个阶段依次实现 Upload session、Chunk receiver、Offset tracker、Integrity checker、Completion assembler，每阶段配套聚焦单测。集成测试组合各模块并驱动真实 large file upload 场景：先验证正常路径，再刻意触发 a client that resumes at the wrong offset after a partial write and corrupts the assembled file 并断言系统降级而非损坏。所有依赖均在进程内或被桩替换，用例在 CI 中确定可复现。

限制与后续

• 单区域设计，多区域复制超出范围。
• Upload session 默认进程内，未水平共享。
• 无鉴权层，假定部署在强制身份的边缘之后。

代码示例

# setup for resumable-upload-service
pnpm init
pnpm add fastify blake3 lmdb
pnpm add -D typescript tsx vitest

resumable_upload_service/
├── src/index.ts
├── src/upload-session.ts
├── src/chunk-receiver.ts
├── tests/resumable_upload_service.test.ts
└── package.json

// Upload session: large file upload core
export function uploadsession(input: UploadsessionInput): UploadsessionResult {
  // Build the upload session that anchors large file upload and defines the core data shape.
  return processUploadsession(input);
}

// Chunk receiver — handles large file upload Add the chunk receiver so
export class Chunkreceiver {
  constructor(private opts: ChunkreceiverOptions) {}
  async run(ctx: Context): Promise<ChunkreceiverOutput> {
    return this.execute(ctx);
  }
}

// Offset tracker: large file upload stage
export const offsettracker = (next: Next) => async (req: Request) => {
  const out = await transform(req);
  return next(out);
};

// Integrity checker for large file upload
export async function integritychecker(stream: AsyncIterable<Chunk>): Promise<Aggregate> {
  let acc = init();
  for await (const c of stream) acc = merge(acc, c);
  return acc;
}

// Completion assembler: large file upload finalization
export function completionassembler(state: State): Result {
  validate(state);
  return finalize(state);
}

# run the large file upload test suite
pnpm vitest run