GO Weirdness Converting Btye array to string from MD5 hash-CodePudding

Could someone enlighten me where I'm going wrong.

I can't convert the byte array produced from the hash sum function by casting with string, I have to use Sprintf.

Here is a snippet of the code:

f, _ := os.Open(filename)
hash := md5.New()
io.Copy(hash, f)
hashStringGood := fmt.Sprintf("%x", hash.Sum(nil))
hashStringJunk := string(hash.Sum(nil)[:])

hasStringGood would result in d41d8cd98f00b204e9800998ecf8427e hashStringJunk would result in ��ُ�� B~

CodePudding user response：

MD5 hash is a 128-bit value. If you convert it to a string, you get 16 bytes of binary data, many of which will be unprintable. You have to convert that to a string using fmt.Sprintf or some other method.

CodePudding user response：

When you convert random binary data to a string without an encoding scheme, it's very unlikely that the data will map to a sequence of printable characters.

The %x verb from the fmt package is a convenience method for hex-encoding binary data. From the "String and slice of bytes" section of the verb definitions in the fmt package documentation:

%s  the uninterpreted bytes of the string or slice
%q  a double-quoted string safely escaped with Go syntax
%x  base 16, lower-case, two characters per byte

Alternatively, you can use packages nested underneath the encoding package to encode the data:

package main

import (
    "crypto/md5"
    "encoding/base64"
    "encoding/hex"
    "fmt"
)

func main() {
    hash := md5.Sum([]byte("input to be hashed"))
    fmt.Printf("Using %%s verb: %s\n", hash)
    fmt.Printf("Using %%q verb: %q\n", hash)
    fmt.Printf("Using %%x verb: %x\n", hash)

    hexHash := hex.EncodeToString(hash[:])
    fmt.Printf("Converted to a hex-encoded string: %s\n", hexHash)

    base64Hash := base64.StdEncoding.EncodeToString(hash[:])
    fmt.Printf("Converted to a base64-encoded string: %s\n", base64Hash)
}

Output

Using %s verb: �����Q���6���5�
Using %q verb: "\x8d\xa8\xf1\xf8\x06\xd3Q\x9d\xa1\xe46\xdb\xfb\x9f5\xd7"
Using %x verb: 8da8f1f806d3519da1e436dbfb9f35d7
Converted to a hex-encoded string: 8da8f1f806d3519da1e436dbfb9f35d7
Converted to a base64-encoded string: jajx AbTUZ2h5Dbb 5811w==

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