duanpai1033 2016-02-18 03:06
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在Go中将结构转换为字节片的紧凑方法是什么?

When writing network code we often find ourselves populating structs from byte slices to access the data in form of an object.

Let's take this struct

type PACKETHEAD struct {
    Type uint16
    Size uint16
    Hash uint32
}

and a byte slice that has been somehow populated with data

data := make([]byte, 1024)

My solution would be to

var pkthead PACKETHEAD
pktsiz := unsafe.Sizeof(pkthead)
pktbuf := bytes.NewReader(buf[:pktsiz])
err = binary.Read(pktbuf, binary.BigEndian, &pkthead)
if err != nil {
    // handle it
}

But

  • It uses unsafe

  • Requires ~7 lines of code for every cast (what if we had hundreds of different packets)

  • Can't be trivially packed into a Cast(*struct, data) function

  • No control over struct padding, what If go's compiler decides to add extra bytes in between members on one end of a network?

  • binary.Read performs a data copy if I'm not mistaken (this isn't necessarily a con)


In C one would just #pragma pack(1) on both network ends, agree on one type of endianess

and finally PACKETHEAD* pkt = (PACKETHEAD*)dataptr;

How can we achieve the same thing with Go?


Have a nice day, Kris

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  • duandou8120 2016-02-18 05:36
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    Shameless plug for gopack, a library I (and others) wrote to support bitpacking in Go. Note: it uses unsafe operations under the hood, if that's a problem.

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