Status code on unresolvable hosts.

[thekvs]

If we try to access through goproxy host which doesn't have DNS record goproxy returns 500 (Internal Server Error) HTTP status code, while squid-cache returns 502 (Bad Gateway) HTTP status code. Shouldn't goproxy simulate squid's behavior?

$ curl -v --proxy 127.0.0.1:3129  --url http://no.exists/
* About to connect() to proxy 127.0.0.1 port 3129 (#0)
*   Trying 127.0.0.1...
* Adding handle: conn: 0x1d71bd0
* Adding handle: send: 0
* Adding handle: recv: 0
* Curl_addHandleToPipeline: length: 1
* - Conn 0 (0x1d71bd0) send_pipe: 1, recv_pipe: 0
* Connected to 127.0.0.1 (127.0.0.1) port 3129 (#0)
> GET http://no.exists/ HTTP/1.1
> User-Agent: curl/7.32.0
> Host: no.exists
> Accept: */*
> Proxy-Connection: Keep-Alive
> 
< HTTP/1.1 500 Internal Server Error
< Content-Type: text/plain; charset=utf-8
< Date: Tue, 20 May 2014 13:13:02 GMT
< Content-Length: 41
< 
dial tcp: lookup no.exists: no such host
* Connection #0 to host 127.0.0.1 left intact
$ 

[thekvs]

Actually squid responds with 503 status code:

HTTP/1.1 503 Service Unavailable
Server: squid/3.3.8
Mime-Version: 1.0
Date: Tue, 20 May 2014 14:47:47 GMT
Content-Type: text/html
Content-Length: 3640
X-Squid-Error: ERR_DNS_FAIL 0
Vary: Accept-Language
Content-Language: en
X-Cache: MISS from ubuntu-v
X-Cache-Lookup: MISS from ubuntu-v:3128
Via: 1.1 ubuntu-v (squid/3.3.8)
Connection: keep-alive

[elazarl]

I apologize for not getting back to you until now.

I'm really not sure what should be the correct response. Can you help me by specifying the use case?

How do you use this information (or is it that you just want to be squid-compliant).

[thekvs]

I just want to somehow detect this situation and show to a user some custom more or less nice looking error page and intercepting 500 "Internal Server Error" seems to me not a very good idea. I think that squid's behavior is more logical in this case.

[marbemac]

+1 On this one. Some of my users are running their own servers (say on localhost:3000), and it'd be great if goproxy could make it easy to distinguish between a server that's not running (ie the user forgot to start it) and a server that responded with a 500.

[elazarl]

I'm convinced. Would fix tonight.

On Thu, Dec 4, 2014, 5:39 PM Marc MacLeod [email protected] wrote:

+1 On this one. Some of my users are running their own servers (say on localhost:3000), and it'd be great if goproxy could make it easy to distinguish between a server that's not running (ie the user forgot to start it) and a server that responded with a 500.

— Reply to this email directly or view it on GitHub https://github.com/elazarl/goproxy/issues/51#issuecomment-65650255.

[mmatczuk]

Any update on that? The correct behavior is to return 502 (not 503) since this is a proxy specific error code. Service Unavailable is a "come back later" I'm busy response.

[lambrospetrou]

@elazarl Is there any progress on this issue, or was it somehow addressed in a different way?

Right now I do the following to handle this:

proxy.OnResponse().DoFunc(func(resp *http.Response, ctx *goproxy.ProxyCtx) *http.Response {
	var dnsError *net.DNSError
	if errors.As(ctx.Error, &dnsError) {
		// Do not leak our server's address.
		dnsError.Server = "<server-redacted>"
		return goproxy.NewResponse(ctx.Req, goproxy.ContentTypeText, http.StatusBadGateway, dnsError.Error())
	}
	return resp
})