去http重用似乎在上传文件中不起作用

When I use my go(1.8) http lib to do normal GET/POST method, it works fine, If I try to upload file to server with the http lib, the client will create a lot of sockets. In my test, files are cut in pieces to upload in 5 goroutines, the client remain 250 sockets. I already add defer resp.Body.Close()，here the key codes:

const (
    MaxIdleConns        int = 40
    MaxIdleConnsPerHost int = 40
)
transport := &http.Transport{
        MaxIdleConns:          MaxIdleConns,
        MaxIdleConnsPerHost:   MaxIdleConnsPerHost,
        IdleConnTimeout:       15 * time.Second,
        ResponseHeaderTimeout: Time.Hour, 
    }
client := &http.Client{
        Transport: transport,
        Timeout:   time.Second * 30,
}

those 250 sockets only recycle after client exit。

It just a silly question，the lib doesn't reuse http client, thanks for help.here my new transport define:

const (
  MaxIdleConnsPerHost = 10
  MaxIdleConns        = 100
)
transport := &http.Transport{
    DialContext: (&net.Dialer{
      Timeout:   30 * time.Second,
      KeepAlive: 30 * time.Second,
      DualStack: true,
    }).DialContext,
    MaxIdleConns:          MaxIdleConns,
    MaxIdleConnsPerHost:   MaxIdleConnsPerHost,
    IdleConnTimeout:       90 * time.Second,
    TLSHandshakeTimeout:   10 * time.Second,
    ExpectContinueTimeout: 5 * time.Second,
}

and i cache the http client instead of new http.Client for every http request. go doc recommand reuse the client

// The Client's Transport typically has internal state (cached TCP // connections), so Clients should be reused instead of created as // needed. Clients are safe for concurrent use by multiple goroutines. https://golang.org/src/net/http/client.go