是否可以计算文件的md5并将文件同时写入磁盘？

I write a file uploader with Go. I would like to have md5 of the file as a file name when I save it to the disk.

What is the best way to solve this problem?

I save a file this way:

reader, _ := r.MultipartReader()
p, _ := reader.NextPart()

f, _ := os.Create("./filename") // here I need md5 as a file name
defer f.Close()

lmt := io.LimitReader(p, maxSize + 1)
written, _ := io.Copy(f, lmt)
if written > maxSize {
    os.Remove(f.Name())
}

here is an example using io.TeeReader to perform both computation and copy at same time

https://play.golang.org/p/IJJQiaeTOBh

package main

import (
    "crypto/sha256"
    "fmt"
    "io"
    "os"
    "strings"
)

func main() {

    var s io.Reader = strings.NewReader("some data")

    // maxSize := 4096
    // s = io.LimitReader(s, maxSize + 1)

    h := sha256.New()
    tr := io.TeeReader(s, h)
    io.Copy(os.Stdout, tr)
    fmt.Printf("
%x", h.Sum(nil))

}
// Output:
//some data
//1307990e6ba5ca145eb35e99182a9bec46531bc54ddf656a602c780fa0240dee

And the comparison test for correctness

$ echo -n "some data" | sha256sum -
1307990e6ba5ca145eb35e99182a9bec46531bc54ddf656a602c780fa0240dee  -

Instead of using io.TeeReader I have used io.MultiWriter to create 2 buffers (I will use the first buffer to calculate md5 and the second to write to a file with md5 name)

lmt := io.LimitReader(buf, maxSize + 1)

hash := md5.New()

var buf1, buf2 bytes.Buffer
w := io.MultiWriter(&buf1, &buf2)

if _, err := io.Copy(w, lmt); err != nil {
    log.Fatal(err)
}
if _, err := io.Copy(hash, &buf1); err != nil {
    log.Fatal(err)
}

fmt.Println("md5 is: ", hex.EncodeToString(hash.Sum(nil)))

// Now we can create file with os.Openfile passing md5 name as an argument + write &buf2 to this file