英文:
Golang - Packing and hashing binary data
问题
我正在尝试学习Golang，并且有Python的背景。我目前正在努力理解如何将变量打包成二进制格式（带有校验和）。在Python中，我会使用类似以下的代码：
import structimport hashliba = 100b = "foo\x00\x00" # 填充到固定长度packet = struct.pack('<B5s', a, b)digest = hashlib.sha256(packet).digest()packet += digest
为了在Go中实现相同的功能，我尝试了以下代码：
package mainimport ("crypto/sha256""fmt""encoding/binary""bytes")type packet struct {a uint8b string}func main() {var p = packet{}p.a = 1p.b = "foo\x00\x00"buf := new(bytes.Buffer)binary.Write(buf, binary.LittleEndian, &p)h := sha256.New()h.Write(buf.Bytes())fmt.Printf("% x\n", p)}
然而，不幸的是，无论我如何尝试，似乎都陷入了变量类型冲突的噩梦（缓冲区、字节数组和字符串）。我希望能得到一些指导，看看我是否采取了正确的方法。
英文:
I'm attempting to learn Golang and have a background in Python. I'm currently trying to get my head around how to pack variables into a binary format (with a checksum). In Python I'd use something like:
import structimport hashliba = 100b = "foo\x00\x00" # Padded to fixed lengthpacket = struct.pack('<B5s', a, b)digest = hashlib.sha256(packet).digest()packet += digest
To do the same thing in Go, I'm trying code like this:
package mainimport ("crypto/sha256""fmt""encoding/binary""bytes")type packet struct {a uint8b string}func main() {var p = packet{}p.a = 1p.b = "foo\x00\x00"buf := new(bytes.Buffer)binary.Write(buf, binary.LittleEndian, &p)h := sha256.New()h.Write(buf.String())fmt.Printf("% x\n", p)}
Unfortunately, however I attack it I seem to get into a nightmare of clashing variable types (buffers, byte arrays and strings). I'd appreciate some guidance as to whether I'm taking even remotely the right approach.
答案1
得分: 5
更新为可工作的代码。
package mainimport ("bytes""crypto/sha256""encoding/binary""fmt")type packet struct {a uint8b []byte}func main() {var p = packet{}p.a = 1p.b = []byte("foo\x00\x00")buf := bytes.Buffer{}err := binary.Write(&buf, binary.BigEndian, p.a)if err != nil {fmt.Println(err)}_, err = buf.Write(p.b)if err != nil {fmt.Println(err)}h := sha256.New()h.Write(buf.Bytes())hash := h.Sum([]byte{})fmt.Printf("% x\n", hash)}
你是对的，使用encoding/binary在结构体中写入可能具有动态长度的项（切片和字符串）确实有些麻烦。你可能会对查看"encoding/gob"包感兴趣，它可以自动编码字符串（尽管它与你这里的填充字符串不兼容）。
英文:
Updated to something that works.
package mainimport ("bytes""crypto/sha256""encoding/binary""fmt")type packet struct {a uint8b []byte}func main() {var p = packet{}p.a = 1p.b = []byte("foo\x00\x00")buf := bytes.Buffer{}err := binary.Write(&buf, binary.BigEndian, p.a)if err != nil {fmt.Println(err)}_, err = buf.Write(p.b)if err != nil {fmt.Println(err)}h := sha256.New()h.Write(buf.Bytes())hash := h.Sum([]byte{})fmt.Printf("% x\n", hash)}
http://play.golang.org/p/t8ltu_WCpe
You're right that it's a bit painful to write structs with possibly dynamic length items in them (slices and strings) using encoding/binary. You might be interested in checking out the "encoding/gob" package that encodes strings automatically (although it isn't compatible with the padded string you've got here).
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