Golang md5 Write vs Sum-为什么输出不同？

Question

Can anyone explain why these methods produce two different output values? It isn't clear from the md5 docs.

import (
    "crypto/md5"
    "encoding/hex"
    "fmt"
)

func GetMD5HashWithWrite(text string) string {
    hasher := md5.New()
    hasher.Write([]byte(text))
    return hex.EncodeToString(hasher.Sum(nil))
}

func GetMD5HashWithSum(text string) string {
    hasher := md5.New()
    return hex.EncodeToString(hasher.Sum([]byte(text)))
}

See example: https://play.golang.org/p/Fy7KgfCvXc

Answer 1

The argument to the Sum function is not input, but a location to store the output. It is technically possible to Sum into a fixed byte array without needing to allocate. You must use Write to provide input to the hash function.

Or use md5.Sum() directly:

func GetMD5HashWithSum(text string) string {
    hash := md5.Sum([]byte(text))
    return hex.EncodeToString(hash[:]) 
}