字符串文字转义十六进制值

Question

I am attempting to escape a specific hex value in a golang string. The function call looks something like this:

Insert(0, "\x00\x00\x00IHDR\x00\x00\x000\x00\x00\x000\b\x03")
Insert(25, "\x00\x00\x00\x06PLTE")
Insert(43, "\x00\x00\x00\x02tRNS")
Insert(57, "\x00\x00\t;IDATx\xDA\x010\t\xCF\xF6") // problem line
Insert(2432, "\x00\x00\x00\x00IEND")

The problem arises when the language interprets the "\xDA" hex escape. Instead of correctly escaping to a Ú value, it is escaped to � (the Replacement Character).

I ensured this is what was occuring in the following playground example:

fmt.Println("\xDA")
i := 218
h := fmt.Sprintf("%x", i)
fmt.Printf("Hex conf of '%d' is '%s'
", i, h)  
fmt.Println(string(i))

This snippet, when run, prints

�
Hex conf of '218' is 'da'
Ú

Am I missing something here? The fact that "\xDA" is being escaped to a value of 65533 is throwing off my entire program, which relies on the CRC32 and some other checksums. This does not occur in the javascript version of this program (which itself is a translation from James compface program, written in C).

Here is the playground link: https://play.golang.org/p/c-XMK68maX

Answer 1

Go strings are just a series of bytes, but when an encoding is needed, it's assumed to be utf8. The value \xda isn't a valid utf8 character, so when printing it's converted to the unicode.ReplacementCharacter "�"

    ReplacementChar = '\uFFFD'     // Represents invalid code points.

If you want the rune value of \xda in a string literal, use a unicode escape: \u00DA, or use the utf8 encoded: \xc3\x9a, or use the character itself: Ú.

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

If you actually want a single byte value of \xda in your string, that is what you have and the printed character is inconsequential.