GoLang：结构中的可变长度数组，用于二进制读取

Question

I'm trying to reimplement a program it did in C a few years ago in Go
The program should read a "record"-like structured binary file and do something with the record (what is done with the records itself is not relevant for this question)

Such a datafile consists of many records where each record has the following definition:

REC_LEN   U2 // length of record after header
REC_TYPE  U1 //a type
REC_SUB   U1 //a subtype
REC_LEN x U1 //"payload" 

My problem now is how to specify that variable length byte[] in a struct in Go?
My plan was to use binary.Read to read the records
Here's what I've tried so far in Go:

type Record struct {
    rec_len uint16
    rec_type uint8
    rec_sub uint8
    data [rec_len]byte
}

Unfortunatelly it seems I can't reference a field of a struct within the same struct as I get the following error:

xxxx.go:15: undefined: rec_len
xxxx.go:15: invalid array bound rec_len

I'd appreciate any ideas pointing me in the right direction
Thanks
KR

Answer 1

You can read the record as follows:

var rec Record

// Slurp up the fixed sized header.

var buf [4]byte
_, err := io.ReadFull(r, buf[:])
if err != nil {
    // handle error
}
rec.rec_len = binary.BigEndian.Uint16(buf[0:2])
rec.rec_type = buf[2]
rec.rec_sub = buf[3]

// Create the variable part and read it.

rec.data = make([]byte, rec.rec_len)
_, err = io.ReadFull(r, rec.data)
if err != nil {
    // handle error
}