hono/deno_dist/utils/filepath.ts

type FilePathOptions = {
  filename: string
  root?: string
  defaultDocument?: string
}

export const getFilePath = (options: FilePathOptions): string | undefined => {
  let filename = options.filename
  if (/(?:^|[\/\\])\.\.(?:$|[\/\\])/.test(filename)) {
    return
  }

  let root = options.root || ''
  const defaultDocument = options.defaultDocument || 'index.html'

  if (filename.endsWith('/')) {
    // /top/ => /top/index.html
    filename = filename.concat(defaultDocument)
  } else if (!filename.match(/\.[a-zA-Z0-9]+$/)) {
    // /top => /top/index.html
    filename = filename.concat('/' + defaultDocument)
  }

  // /foo.html => foo.html
  filename = filename.replace(/^\.?[\/\\]/, '')

  // foo\bar.txt => foo/bar.txt
  filename = filename.replace(/\\/, '/')

  // assets/ => assets
  root = root.replace(/\/$/, '')

  // ./assets/foo.html => assets/foo.html
  let path = root ? root + '/' + filename : filename
  path = path.replace(/^\.?\//, '')

  return path
}