The redirect function allows to avoid a parameter for the Location

[AndyBitz]

Bug report

Describe the bug

The redirect function added in #14705 allows to set a status code or URL as second argument, and an optional third argument for the URL if the second argument was used for the status code.

However, the function signature allows setting a status code without providing a URL. In those cases the Location header would be set to undefined, which throws an error.

To Reproduce

• Create a Next.js project with TypeScript
• Create pages/api/index.ts with this content:

import { NextApiRequest, NextApiResponse } from 'next';
export default (req: NextApiRequest, res: NextApiResponse) => res.redirect(307);

• Run next dev and execute curl localhost:300/api
• 500 Status code is returned and error is logged

TypeError [ERR_HTTP_INVALID_HEADER_VALUE]: Invalid value "undefined" for header "Location"
    at ServerResponse.setHeader (_http_outgoing.js:521:3)
    at setHeadersFromObject (/private/tmp/nextjs/node_modules/next/dist/compiled/compression/index.js:1:145242)
    at ServerResponse.setWriteHeadHeaders (/private/tmp/nextjs/node_modules/next/dist/compiled/compression/index.js:1:145476)
    at ServerResponse.writeHead (/private/tmp/nextjs/node_modules/next/dist/compiled/compression/index.js:1:144683)
    at redirect (/private/tmp/nextjs/node_modules/next/dist/next-server/server/api-utils.js:32:114)
    at ServerResponse.apiRes.redirect (/private/tmp/nextjs/node_modules/next/dist/next-server/server/api-utils.js:6:340)
    at __webpack_exports__.default (webpack-internal:///./pages/api/index.js:2:82)
    at apiResolver (/private/tmp/nextjs/node_modules/next/dist/next-server/server/api-utils.js:8:7)
    at runMicrotasks (<anonymous>)
    at processTicksAndRejections (internal/process/task_queues.js:97:5) {
  code: 'ERR_HTTP_INVALID_HEADER_VALUE'
}

Expected behavior

TypeScript should have caught the error upfront.

Personally I think it'd make more sense to have a signature like this:

function redirect(url: string, status: number = 307);

so that no matter what, the Location will always be set and won't depend on the type. But this might be impossible to change now. I'm not sure if it'd make sense to throw a custom error if the URL parameter was forgotten.

Maybe it'd also be enough to rely on the number of arguments instead of their type.

System information

• OS: macOS
• Version of Next.js: 9.5.0
• Version of Node.js: v12.18.3

[balazsorban44]

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