A way to completly overwrite response from middleware after next()

[TorbjornHoltmon]

This is a very niche issue.

We use Hono for many things, including our Cloudflare workers' proxy.
The proxy sits on top of our domain and routes traffic to different workers and other external servers.

When you proxy a request from a worker, the response that Hono gets is a fetch response, and you cannot change headers.

When we use middleware in our proxy, there is no way for us to re-write the response since ´contex.res´ has a set that manipulates the headers.

https://github.com/honojs/hono/blob/fea78f29bd681350ce61dd71b33042aa6ec7db5c/src/context.ts#LL101-L110C4

  set res(_res: Response) {
    if (this._res) {
      this._res.headers.delete('content-type')
      this._res.headers.forEach((v, k) => {
        _res.headers.set(k, v)
      })
    }
    this._res = _res
    this.finalized = true
  }

Not many people will have this issue, but we could really use some type of overwrite on the response so that we can write middleware that does something like this:

export const cookieMiddleware: MiddlewareHandler<HonoEnv> = async (c, next) => {
    await next()
    if(c.res.headers.has("special-header")) {
      // We cannot use res.headers, so we clone the headers
      const clonedHeaders = cloneResponseHeaders(c.res)
      clonedHeaders.append('Set-Cookie', "cookie goes here")
        
      // create a new response from the old
      const newResponse = new Response(c.res.body, {
        headers: clonedHeaders,
        status: c.res.status,
      })
      // some way to overwrite response, just an example
      c.overwriteResponse(newResponse)
    }
}

If only the set did not change headers we could have used that

 set res(_res: Response) {
    this._res = _res
    this.finalized = true
  }

Maybe this is something that should be contained in its own world. "hono/proxy". Which is meant to handle things as a proxy and not api.

[yusukebe]

Hi @TorbjornHoltmon !

I have ideas about this "middleware matter". I'll let you know later.

[yusukebe]

Hi @TorbjornHoltmon !

I've created PR #970 . With this PR, you can do it by putting undefined:

app.use('*', async (c, next) => {
  await next()
  c.res = undefined
  c.res = new Response('New Response')
})

This way does not include breaking changes and makes it possible what you want to do.

[yusukebe]

I think we can close this issue. Thanks.

[fzn0x]

Hi, can you document this feature ? @yusukebe I think this is really helpful for custom middleware. I just found the feature was implemented here.

[yusukebe]

Hi @fzn0x

Created the issue honojs/website#317 on the website repo. We'll do that.