是否可以计算文件的md5并将文件同时写入磁盘？

Question

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())
}

Answer 1

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  -