如何使用go http.Client（和应用程序引擎urlfetch）仅下载大文件的开头

Question

I'm trying to download only the first 1kb of large files using http.Client in go, but it seems like response.Body is always fully buffered. Is there a control over how much to buffer?

If so, how can this be used with app engine urlfetch service?

The following works fine with app engine urlfetch in python, and I'm trying to port this to go:

from urllib2 import urlopen
req = Request(url)
urlopen(req).read(1024) # Read the first 1kb.

Answer 1

Setting "Range" Request Header attribute to "bytes=0-1023" should work.

package main

import (
    "fmt"
    "io/ioutil"
    "net/http"
)

func main() {
    req, _ := http.NewRequest("GET", "http://example.com", nil)
    req.Header.Add("Range", "bytes=0-1023")
    fmt.Println(req)
    var client http.Client
    resp, _ := client.Do(req)
    fmt.Println(resp)
    body, _ := ioutil.ReadAll(resp.Body)
    fmt.Println(len(body))
}

Same thing should work for http.Client provieded in app engine.