Golang：从一个字节解析位值

Question

I need to parse a network packet which consists of two bytes: first one consists of 8 bits that set certain flags depending on their order (for instance) and the second one is uint8 (which is simple)

• 1 - online
• 0 - not active
• 1 - isPretty
• 1 - isHandsome
• 0 - bald
• 0 - deaf
• 0 - mute
• 0 - blind

How do I parse it from a byte primitive?

Answer 1

Some useful Go standard library packages for dealing with binary:

• encoding/binary
• math/bits

For extracting single bits from a byte, you ought to use bitwise operators - |, & and >>.

For example:

package main

import (
    "fmt"
)

func main() {
    v := byte(0xB2)
    if (v >> 4) & 1 == 1 {
        fmt.Println("bit 4 (counting from 0) is set")
    }
}

This checks bit 4 (with bit 0 being the lowest bit in the byte) by shifting the byte value 4 positions to the right and AND-ing with 1. You can check the other bits in your flag value similarly. Feel free to write a function that replaces the 4 in the sample above with an argument N to check bit number N.

You can find more examples in other SO answers like this one or the ones @icza linked to in a comment.