How to Dump Structs with Unexported Fields into Byte Arrays in Go without Reflection?

Dumping Struct into Byte Array without Reflection

The question stems from an issue faced when using the encoding/binary package to dump structs into byte arrays. Since the package relies on reflection, it fails to handle unexported (uncapitalized) struct fields. The concern arises from the attempt to maintain the abstraction of certain data structs.

Solution

To dump structs with unexported fields into byte arrays without reflection, consider employing the gob package. This package provides efficient and platform-independent serialization and deserialization capabilities. By implementing the GobEncoder and GobDecoder interfaces for structs with unexported fields, you can effectively serialize and deserialize their contents.

Below is an example demonstrating the use of the gob package:

package main

import (
    "bytes"
    "encoding/gob"
    "fmt"
    "log"
)

type Data struct {
    id   int32
    name [16]byte
}

func (d *Data) GobEncode() ([]byte, error) {
    w := new(bytes.Buffer)
    encoder := gob.NewEncoder(w)
    err := encoder.Encode(d.id)
    if err != nil {
        return nil, err
    }
    err = encoder.Encode(d.name)
    if err != nil {
        return nil, err
    }
    return w.Bytes(), nil
}

func (d *Data) GobDecode(buf []byte) error {
    r := bytes.NewBuffer(buf)
    decoder := gob.NewDecoder(r)
    err := decoder.Decode(&d.id)
    if err != nil {
        return err
    }
    return decoder.Decode(&d.name)
}

func main() {
    d := Data{id: 7}
    copy(d.name[:], []byte("tree"))
    buffer := new(bytes.Buffer)

    // Writing
    enc := gob.NewEncoder(buffer)
    err := enc.Encode(d)
    if err != nil {
        log.Fatal("encode error:", err)
    }

    // Reading
    buffer = bytes.NewBuffer(buffer.Bytes())
    e := new(Data)
    dec := gob.NewDecoder(buffer)
    err = dec.Decode(e)
    fmt.Println(e, err)
}

By implementing these interfaces, you can serialize and deserialize unexported struct fields without the need for reflection, ensuring the proper dumping of struct data into byte arrays.

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