构建图片缩放管道

项目概述

本项目实现一个面向 image processing 的完整系统，核心要解决的问题是 producing multiple resized derivatives from a source image efficiently and without blocking on a single large decode。整体由 Decode pool、Resize worker、Format encoder、Derivative planner、Cache writer 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 malformed image that triggers a decode crash and takes down the worker pool for every other request 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 source image decoded once and resized into several target dimensions, each encoded and cached keyed by source hash and size。Decode pool 定义其余阶段共同依赖的数据形状并在边界处校验输入；Resize worker 承载 image processing 的正确性逻辑；Format encoder 专门处理 a malformed image that triggers a decode crash and takes down the worker pool for every other request，在失败路径上给出明确的拒绝、重试或降级策略；Derivative planner 提供可观测性，每次操作输出带关联 id 的结构化事件；Cache writer 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 Decode pool、Resize worker、Format encoder、Derivative planner、Cache writer，每阶段配套聚焦单测。集成测试组合各模块并驱动真实 image processing 场景：先验证正常路径，再刻意触发 a malformed image that triggers a decode crash and takes down the worker pool for every other request 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。
• Decode pool 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 image-resize-pipeline
pnpm init
pnpm add sharp fastify
pnpm add -D typescript tsx vitest

image_resize_pipeline/
├── src/index.ts
├── src/decode-pool.ts
├── src/resize-worker.ts
├── tests/image_resize_pipeline.test.ts
└── package.json

// Decode pool: image processing core
export function decodepool(input: DecodepoolInput): DecodepoolResult {
  // Build the decode pool that anchors image processing and defines the core data shape.
  return processDecodepool(input);
}

// Resize worker — handles image processing Add the resize worker so
export class Resizeworker {
  constructor(private opts: ResizeworkerOptions) {}
  async run(ctx: Context): Promise<ResizeworkerOutput> {
    return this.execute(ctx);
  }
}

// Format encoder: image processing stage
export const formatencoder = (next: Next) => async (req: Request) => {
  const out = await transform(req);
  return next(out);
};

// Derivative planner for image processing
export async function derivativeplanner(stream: AsyncIterable<Chunk>): Promise<Aggregate> {
  let acc = init();
  for await (const c of stream) acc = merge(acc, c);
  return acc;
}

// Cache writer: image processing finalization
export function cachewriter(state: State): Result {
  validate(state);
  return finalize(state);
}

# run the image processing test suite
pnpm vitest run