GO weirdness converting Btye array from MD5 hash to string

Question content

Can someone tell me what's wrong?

I cannot convert the byte array produced by the hash sum function via string conversion, I have to use sprintf.

This is the code snippet:

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

hasstringgood will result in d41d8cd98f00b204e9800998ecf8427e hashstringjunk will result in ��ُ�� ���b~

Correct answer

when you convert random binary data to no encoding scheme string, the data is unlikely to map to a sequence of printable characters.

The %x verb from the fmt package is a convenience method for hexadecimal encoding of binary data. From the "Strings and Byte Slicing" section of the verb definition 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 encode the data using a package nested under the encoding package:

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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