manuall_cookie_set.js

function setPreviewData<T>(
  res: NextApiResponse<T>,
  data: object | string, // TODO: strict runtime type checking
  options: {
    maxAge?: number
  } & __ApiPreviewProps
): NextApiResponse<T> {
  if (
    typeof options.previewModeId !== 'string' ||
    options.previewModeId.length < 16
  ) {
    throw new Error('invariant: invalid previewModeId')
  }
  if (
    typeof options.previewModeEncryptionKey !== 'string' ||
    options.previewModeEncryptionKey.length < 16
  ) {
    throw new Error('invariant: invalid previewModeEncryptionKey')
  }
  if (
    typeof options.previewModeSigningKey !== 'string' ||
    options.previewModeSigningKey.length < 16
  ) {
    throw new Error('invariant: invalid previewModeSigningKey')
  }

  const jsonwebtoken = require('next/dist/compiled/jsonwebtoken') as typeof import('jsonwebtoken')

  const payload = jsonwebtoken.sign(
    {
      data: encryptWithSecret(
        Buffer.from(options.previewModeEncryptionKey),
        JSON.stringify(data)
      ),
    },
    options.previewModeSigningKey,
    {
      algorithm: 'HS256',
      ...(options.maxAge !== undefined
        ? { expiresIn: options.maxAge }
        : undefined),
    }
  )

  // limit preview mode cookie to 2KB since we shouldn't store too much
  // data here and browsers drop cookies over 4KB
  if (payload.length > 2048) {
    throw new Error(
      `Preview data is limited to 2KB currently, reduce how much data you are storing as preview data to continue`
    )
  }

  const {
    serialize,
  } = require('next/dist/compiled/cookie') as typeof import('cookie')
  const previous = res.getHeader('Set-Cookie')
  res.setHeader(`Set-Cookie`, [
    ...(typeof previous === 'string'
      ? [previous]
      : Array.isArray(previous)
      ? previous
      : []),
    serialize(COOKIE_NAME_PRERENDER_BYPASS, options.previewModeId, {
      httpOnly: true,
      sameSite: process.env.NODE_ENV !== 'development' ? 'none' : 'lax',
      secure: process.env.NODE_ENV !== 'development',
      path: '/',
      ...(options.maxAge !== undefined
        ? ({ maxAge: options.maxAge } as CookieSerializeOptions)
        : undefined),
    }),
    serialize(COOKIE_NAME_PRERENDER_DATA, payload, {
      httpOnly: true,
      sameSite: process.env.NODE_ENV !== 'development' ? 'none' : 'lax',
      secure: process.env.NODE_ENV !== 'development',
      path: '/',
      ...(options.maxAge !== undefined
        ? ({ maxAge: options.maxAge } as CookieSerializeOptions)
        : undefined),
    }),
  ])
  return res
}