bf089562c7
_Hello Next.js team! First PR here, I hope I've followed the right practices._ ### What's in there? It has been decided to only support the following uses cases in Next.js' middleware: - rewrite the URL (`x-middleware-rewrite` response header) - redirect to another URL (`Location` response header) - pass on to the next piece in the request pipeline (`x-middleware-next` response header) 1. during development, a warning on console tells developers when they are returning a response (either with `Response` or `NextResponse`). 2. at build time, this warning becomes an error. 3. at run time, returning a response body will trigger a 500 HTTP error with a JSON payload containing the detailed error. All returned/thrown errors contain a link to the documentation. This is a breaking feature compared to the _beta_ middleware implementation, and also removes `NextResponse.json()` which makes no sense any more. ### How to try it? - runtime behavior: `HEADLESS=true yarn jest test/integration/middleware/core` - build behavior : `yarn jest test/integration/middleware/build-errors` - development behavior: `HEADLESS=true yarn jest test/development/middleware-warnings` ### Notes to reviewers The limitation happens in next's web adapter. ~The initial implementation was to check `response.body` existence, but it turns out [`Response.redirect()`](https://github.com/vercel/next.js/blob/canary/packages/next/server/web/spec-compliant/response.ts#L42-L53) may set the response body (https://github.com/vercel/next.js/pull/31886). Hence why the proposed implementation specifically looks at response headers.~ `Response.redirect()` and `NextResponse.redirect()` do not need to include the final location in their body: it is handled by next server https://github.com/vercel/next.js/blob/canary/packages/next/server/next-server.ts#L1142 Because this is a breaking change, I had to adjust several tests cases, previously returning JSON/stream/text bodies. When relevant, these middlewares are returning data using response headers. About DevEx: relying on AST analysis to detect forbidden use cases is not as good as running the code. Such cases are easy to detect: ```js new Response('a text value') new Response(JSON.stringify({ /* whatever */ }) ``` But these are false-positive cases: ```js function returnNull() { return null } new Response(returnNull()) function doesNothing() {} new Response(doesNothing()) ``` However, I see no good reasons to let users ship middleware such as the one above, hence why the build will fail, even if _technically speaking_, they are not setting the response body. ## Feature - [x] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR. - [ ] Related issues linked using `fixes #number` - [x] Integration tests added - [x] Documentation added - [ ] Telemetry added. In case of a feature if it's used or not. - [x] Errors have helpful link attached, see `contributing.md` ## Documentation / Examples - [x] Make sure the linting passes by running `yarn lint`
43 lines
1.5 KiB
TypeScript
43 lines
1.5 KiB
TypeScript
import { getModuleBuildInfo } from './get-module-build-info'
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import { stringifyRequest } from '../stringify-request'
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import { MIDDLEWARE_FILE } from '../../../lib/constants'
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export type MiddlewareLoaderOptions = {
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absolutePagePath: string
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page: string
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}
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export default function middlewareLoader(this: any) {
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const { absolutePagePath, page }: MiddlewareLoaderOptions = this.getOptions()
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const stringifiedPagePath = stringifyRequest(this, absolutePagePath)
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const buildInfo = getModuleBuildInfo(this._module)
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buildInfo.nextEdgeMiddleware = {
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page: page.replace(new RegExp(`${MIDDLEWARE_FILE}$`), '') || '/',
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}
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return `
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import { adapter, blockUnallowedResponse } from 'next/dist/server/web/adapter'
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// The condition is true when the "process" module is provided
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if (process !== global.process) {
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// prefer local process but global.process has correct "env"
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process.env = global.process.env;
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global.process = process;
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}
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var mod = require(${stringifiedPagePath})
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var handler = mod.middleware || mod.default;
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if (typeof handler !== 'function') {
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throw new Error('The Middleware "pages${page}" must export a \`middleware\` or a \`default\` function');
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}
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export default function (opts) {
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return blockUnallowedResponse(adapter({
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...opts,
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page: ${JSON.stringify(page)},
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handler,
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}))
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}
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`
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}
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