# Data flow — koajs/koa

> Canonical page: https://codevetter.com/unpack/koa/data-flow

# Data flow — koajs/koa

Scanned commit 824c1cf8de9a91a2941973b25dc8a3d3029b9e4f (2026-09-18). Generated by codevetter codevetter 1.15.0 on 2026-10-02.

Source inspection; upstream code and tests were not executed.

Incoming Node HTTP objects remain the transport owners throughout a request. Koa adds linked wrappers, lazy parsers, and a middleware-visible state namespace. Outgoing body assignment prepares metadata, and a separate responder handles serialization or streaming.
- callback() receives req/res, constructs a context, and either invokes handleRequest directly or runs it inside ctxStorage.run(ctx). — [lib/application.js#L182-195](https://github.com/koajs/koa/blob/824c1cf8de9a91a2941973b25dc8a3d3029b9e4f/lib/application.js#L182-L195)
- Context construction creates wrapper instances from application prototypes but preserves references to the original transport objects; state is allocated independently for each request. — [lib/application.js#L228-243](https://github.com/koajs/koa/blob/824c1cf8de9a91a2941973b25dc8a3d3029b9e4f/lib/application.js#L228-L243)
- ctx.query reads req.url through querystring and parseurl, caches by raw query string, and uses URLSearchParams to collapse single values or retain repeated values as arrays. — [lib/request.js#L172-198](https://github.com/koajs/koa/blob/824c1cf8de9a91a2941973b25dc8a3d3029b9e4f/lib/request.js#L172-L198) [lib/search-params.js#L24-31](https://github.com/koajs/koa/blob/824c1cf8de9a91a2941973b25dc8a3d3029b9e4f/lib/search-params.js#L24-L31)
- Assigning query serializes string/number values and repeated array entries; unsupported value types become empty strings before querystring updates req.url. — [lib/search-params.js#L4-21](https://github.com/koajs/koa/blob/824c1cf8de9a91a2941973b25dc8a3d3029b9e4f/lib/search-params.js#L4-L21) [lib/request.js#L185-186](https://github.com/koajs/koa/blob/824c1cf8de9a91a2941973b25dc8a3d3029b9e4f/lib/request.js#L185-L186) [lib/request.js#L208-215](https://github.com/koajs/koa/blob/824c1cf8de9a91a2941973b25dc8a3d3029b9e4f/lib/request.js#L208-L215)
- Forwarded IP input is read from app.proxyIpHeader only in proxy mode, optionally right-trimmed by maxIpsCount, then memoized as ip with socket.remoteAddress fallback. — [lib/request.js#L445-474](https://github.com/koajs/koa/blob/824c1cf8de9a91a2941973b25dc8a3d3029b9e4f/lib/request.js#L445-L474)
- ctx.body delegates to response.body, which stores _body and selects status, content type, length, cleanup, or Response-derived headers before transmission. — [lib/context.js#L195-209](https://github.com/koajs/koa/blob/824c1cf8de9a91a2941973b25dc8a3d3029b9e4f/lib/context.js#L195-L209) [lib/response.js#L135-175](https://github.com/koajs/koa/blob/824c1cf8de9a91a2941973b25dc8a3d3029b9e4f/lib/response.js#L135-L175) [lib/response.js#L181-231](https://github.com/koajs/koa/blob/824c1cf8de9a91a2941973b25dc8a3d3029b9e4f/lib/response.js#L181-L231)
- respond() ends strings/buffers directly, converts WHATWG bodies into Node Readables for pipeline, and JSON-stringifies remaining values while recalculating byte length. — [lib/application.js#L331-351](https://github.com/koajs/koa/blob/824c1cf8de9a91a2941973b25dc8a3d3029b9e4f/lib/application.js#L331-L351)
- Cookie data crosses the HTTP boundary through the cookies dependency using req/res, app.keys, and request.secure; Koa's context getter retains only the per-request cookie helper. — [lib/context.js#L164-175](https://github.com/koajs/koa/blob/824c1cf8de9a91a2941973b25dc8a3d3029b9e4f/lib/context.js#L164-L175) [docs/api/context.md#L69-93](https://github.com/koajs/koa/blob/824c1cf8de9a91a2941973b25dc8a3d3029b9e4f/docs/api/context.md#L69-L93) [__tests__/context/cookies.test.js#L45-62](https://github.com/koajs/koa/blob/824c1cf8de9a91a2941973b25dc8a3d3029b9e4f/__tests__/context/cookies.test.js#L45-L62)

Every claim links to its cited files at the pinned commit. Citations identify source evidence; they do not establish runtime correctness. Independent CodeVetter scan — not reviewed by upstream maintainers.

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