Go中的多部分HTTP请求

I'm attempting to use Go to write a utility that authenticates and uploads a file by making a multipart http request to our server. Everything seems to go okay, except the file is not arriving on the server. Looking at it further it appears the multipart in the request is empty. Code and request output below. What am I missing in my Go code?

The Code: (I've changed the URL...)

package main

import (
    "net/http"
    "mime/multipart"
    "strings"
    "fmt"
    "io/ioutil"
    "io"
    "os"
    "bytes"
    "flag"
    "encoding/json"
)

var (
    filename = flag.String("filename", "", "file to upload")
    name = flag.String("name", "", "name to give file on server")
    username = flag.String("username", "", "username for authentication")
    password = flag.String("password", "", "password for authentication")
)

func main() {
    flag.Parse()

    // Create multipart
    var b bytes.Buffer
    w := multipart.NewWriter(&b)
    f, _ := os.Open(*filename) //open file to send
    defer f.Close()
    fw, err := w.CreateFormFile("file", *name) //give file a name
    if err != nil {
        fmt.Println(err)
    }
    if _, err :=  io.Copy(fw, f); err != nil { //copy the file to the multipart buffer
        fmt.Println(err)
    }
    w.Close()

    // print the head of the multipart data
    bs := b.Bytes()
    fmt.Printf("%+v

", string(bs[:1000]))

    // Send authentication/login
    r, e := http.Post("https://mysite/login", "application/json", strings.NewReader(fmt.Sprintf("{\"username\":\"%s\",\"password\":\"%s\"}", *username, *password)))

    if e != nil {
        fmt.Println(e)
    } else {
        // Get the token from the body
        type Body struct {
            Token string
        }
        // convert json to get the token
        body, _ := ioutil.ReadAll(r.Body)
        bd := bytes.NewBuffer(body)
        dec := json.NewDecoder(bd)
        var m Body
        dec.Decode(&m)

        // Upload file
        req, err := http.NewRequest("POST", "https://mysite/api/apps", &b)
        if err != nil {
            fmt.Printf("%v
", err)
        }
        req.Header.Set("Authentication", fmt.Sprintf("Bearer: %s", m.Token))
        req.Header.Set("Content-Type", w.FormDataContentType())
        client := &http.Client{}
        res, err := client.Do(req)
        if err != nil {
            fmt.Printf("%v
", err)
        }
        // print status and request body
        fmt.Println(res.Status)
        fmt.Printf("%+v
", res.Request)
    }
}

The first thing I print is the byte buffer, b, which contains the multipart data, everything looks good from here. (it was an xml file)

--83451b003d8e5cc38c0e8f60ad318e522cad4818cf293745c84ec36d26d5
Content-Disposition: form-data; name="file"; filename="snapshot-162224-820-99"
Content-Type: application/octet-stream

<manifest>
  <projects>
    <project name=........

Next I print the status of the request.

200 OK

Then I printed out the request structure, here is where I saw the MultipartForm was empty.

&{Method:GET URL:https://mysite/home/ Proto: ProtoMajor:0 ProtoMinor:0 Header:map[Authentication:[Bearer: DY0LCJL0g] Content-Type:[multipart/form-data; boundary=83451b003d8e5cc38c0e8f60ad318e522cad4818cf293745c84ec36d26d5] Referer:[http://mysite/home/]] Body:<nil> GetBody:<nil> ContentLength:0 TransferEncoding:[] Close:false Host: Form:map[] PostForm:map[] MultipartForm:<nil> Trailer:map[] RemoteAddr: RequestURI: TLS:<nil> Cancel:<nil> Response:0xc42018a360 ctx:<nil>}

I highly doubt if the server really received nothing. The behavior of the printed body having a nil body is expected and documented in http.Response

    // Request is the request that was sent to obtain this Response.
    // Request's Body is nil (having already been consumed).
    // This is only populated for Client requests.
    Request *Request

If you want to debug the request body sented, you should either use a mock server or a proxy.

On another note, your code's attempt to login is not going to work. It does not maintain the cookie of login info, so the later requests cannot utilize them.