net/http: client action when doing redirection

[mmpei]

go version 1.11.2.
i use http.client to get an object from an object storage server continually.
the server will response with status code 307 and a redirection url.
my code like:

for ; true;  {
		go func() {
			url := "http://storage.server.com/key/object1"
			client := http.Client{
			}
			resp, err := client.Get(url)
			if err != nil {
				return 
			}
			if resp.Body != nil {
				defer resp.Body.Close()
			}
			//	ioutil.ReadAll(resp.Body)    // this special line
		}()
	}

if uncomment the special line it works as my expection, object will be downloaded continually and data stream could be watched from network card,

# dstat -n 1
 recv  send
1679M 4241k
1728M 4632k
1710M 3984k
1699M 4007k
1777M 3957k
 804M 2591k
1967M 8078k
1558M 4155k
1308M 2821k
1484M 3211k
1430M 3076k
1610M 3915k

if comment the special line, the http.client will also send a request to the redirection url, but no as much as data stream be watched in network card. i doubt that the objects didn't be downloaded.

# dstat -n 1
  10M 2289k
  11M 2289k
  12M 1797k
  13M 2428k
 210k  149k
9356k 2103k
  12M 2361k
  11M 2073k
  11M 2040k

my question is what's the difference between processing http response with and without 'ioutil.ReadAll(resp.Body)'.
could anyone help me to resolve my confusion? thanks.

[andybons]

@bradfitz

[mmpei]

@bradfitz would you help to answer? thank you.

[bradfitz]

Sorry, but I don't understand the question or problem.

[mmpei]

sorry, i update my question. @bradfitz
in brief my question is what's the difference between processing http response with and without 'ioutil.ReadAll(resp.Body)'.
i find that no data stream in network card if without 'ioutil.ReadAll(resp.Body)' and doubt whether the object be downloaded.

by the way there is a redirection in http invoke.

[bradfitz]

If you close a response body without reading from it, the net/http package has the right to just close the TCP connection, as that's usually more efficient that reading bytes just to discard them. See docs at https://golang.org/pkg/net/http/#Client.Do

[mmpei]

so if the returned error is nil, does http.client guarantee that all the requests is sent correctly and all response data is fetched to local even if the reponse data is large?
you can see my test result above, it seems that no data stream in network card when comment 'ioutil.ReadAll()'