The file server seems to have some points where the implementation could be refactored.

• HEAD request support
  Golang's std server and hyper-staticfile seem to support this.
  I think it's easy to implement just by conditionally branching with req.method === "HEAD".

• In recent versions of Deno, the Date header is automatically set if it's not present. So I think adding the Date header inside setBaseHeader() is unnecessary.
  (chore(http/file_server): remove unnecessary Date header generation #3364)
  https://github.com/denoland/deno_std/blob/699ba98572f28e6dfb423abe959502ba6a96c551/http/file_server.ts#L328-L334

• Inside serveDirIndex there are serial await calls. It seems that it can be speeded up by calling this in parallel.
  (perf(http/file_server): read fileinfo in parallel #3363)

  for await (const entry of Deno.readDir(dirPath)) {
    ...
    const fileInfo = await Deno.stat(filePath);
    ...
  } // https://github.com/denoland/deno_std/blob/699ba98572f28e6dfb423abe959502ba6a96c551/http/file_server.ts#L282

• Currently it returns content with 200 OK for paths like /path//////to////file.txt. I think such requests should be redirected to a normalized path. (fix(http/file_server): Redirect non-canonical URL to canonical URL #3362)

• It would be nice to use JSDoc's @module tag to enhance the documentation. (chore(http/file_server): add module documentation #3368)

I will submit a PR on these points later.