http.Client.Do(req) vs. transport.RoundTrip(req)

[Gyu-Ho Lee]

I saw Andrew using RoundTrip in his code (https://github.com/nf/dl/blob/master/dl.go#L165). 

And have been trying to understand when to use RoundTrip and when to use Client.Do.

I am running the following code in my local machine:

http://play.golang.org/p/x6E0T1Hyfz

client, transport := NewClient()

req, err := http.NewRequest("HEAD", "http://google.com", nil)

transport.RoundTrip(req)

client.httpClient.Do(req)

And  `RoundTrip` always takes much less for `HEAD` request to http://google.com

301 Moved Permanently

RoundTrip took: 51.102069ms

200 OK

Client took: 129.125018ms

1. RoundTrip takes less time to finish.

Is it because RoundTrip makes single HTTP transaction(http://golang.org/src/pkg/net/http/client.go)?

2. What do we mean by `RoundTrip should not attempt to interpret the response.`? 

Then when do we use RoundTripper?

3. Why does RoundTrip return 301 instead of 200?

Guess I am just confused about RoundTripper in general.

Thanks in advance.

[James Bardin]

On Monday, November 3, 2014 3:37:38 PM UTC-5, Gyu-Ho Lee wrote:

1. RoundTrip takes less time to finish.

Is it because RoundTrip makes single HTTP transaction(http://golang.org/src/pkg/net/http/client.go)?

Yes. If you get a 3xx response, it will take multiple requests.

 

2. What do we mean by `RoundTrip should not attempt to interpret the response.`? 

Then when do we use RoundTripper?

Use RoundTripper when the client doesn't provide what you need for some reason. Generally the Client is what you want.

 

3. Why does RoundTrip return 301 instead of 200?

For the reason in #2 -- it can't interpret the response. The Client is what handles redirects for you

 

Guess I am just confused about RoundTripper in general.

Read through the client code and wee what else it provides on top of RoundTripper. 

[Andrew Gerrand]

James is right. The Client is more appropriate in most cases.

In my program I didn't need to follow redirects nor handle cookies, so I went straight for http.DefaultTransport.

If in doubt, read the code.

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[Andrew Gerrand]

On Tue Nov 04 2014 at 7:37:44 AM Gyu-Ho Lee <gyuh...@gmail.com> wrote:

2. What do we mean by `RoundTrip should not attempt to interpret the response.`? 

Then when do we use RoundTripper?

Those comments are for *implementers* of the RoundTripper interface. A RoundTripper should make a request and return the response; that's all.

Andrew 

[Gyu-Ho Lee]

Now I understand more. Very much appreciate your answers!

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