Exceeding request_body's max_size returns 502 Bad Gateway

[tribut]

This appears to be a regression from #4558, setting max_size causes a 502 error with this configuration when a large file is uploaded:

http:// {
	request_body {
		max_size 20MB
	}

	handle_path /api/* {
		reverse_proxy api:80
	}
}

I'm using Caddy 2.6.4 (from Docker Hub).

Log entry:

{
  "level": "error",
  "ts": 1690267490.8453255,
  "logger": "http.log.error",
  "msg": "readfrom tcp 172.120.4.5:53858->172.120.4.3:80: {id=tzchyd2sh} requestbody.errorWrapper.Read (requestbody.go:63): HTTP 413: http: request body too large",
  "request": {
    "remote_ip": "172.120.4.1",
    "remote_port": "43776",
    "proto": "HTTP/1.1",
    "method": "POST",
    "host": "localhost:1080",
    "uri": "/api/upload/",
    "headers": {
      "Referer": [
        "http://localhost:1080/test"
      ],
      "Sec-Fetch-Dest": [
        "empty"
      ],
      "Accept-Encoding": [
        "gzip, deflate, br"
      ],
      "Sec-Fetch-Site": [
        "same-origin"
      ],
      "Dnt": [
        "1"
      ],
      "Accept": [
        "*/*"
      ],
      "Content-Type": [
        "multipart/form-data; boundary=---------------------------26304888236811446562077596232"
      ],
      "User-Agent": [
        "Mozilla/5.0 (X11; Linux x86_64; rv:109.0) Gecko/20100101 Firefox/116.0"
      ],
      "Content-Length": [
        "24670389"
      ],
      "Cookie": [],
      "Sec-Fetch-Mode": [
        "cors"
      ],
      "Origin": [
        "http://localhost:1080"
      ],
      "Connection": [
        "keep-alive"
      ],
      "Pragma": [
        "no-cache"
      ],
      "Accept-Language": [
        "de-DE,de;q=0.8,en-US;q=0.5,en;q=0.3"
      ],
      "Cache-Control": [
        "no-cache"
      ]
    }
  },
  "duration": 0.060551495,
  "status": 502,
  "err_id": "nt27mkz4e",
  "err_trace": "reverseproxy.statusError (reverseproxy.go:1299)"
}

[mholt]

(Deleted my previous comment as I was mobile at the time and didn't see the full log)

[mholt]

Thanks for the report! In my experiments, the patch above fixed it. Feel free to verify if you please 😃

My config file:

:8080 {
	request_body {
		max_size 10
	}
	reverse_proxy localhost:1234
}

:1234 {
	respond {http.request.body}
}