How to Handle Binary Data in Go JSON Encoding?

Encoding []byte Strings in JSON Using Go

Problem: Unexpected JSON Encoding of Binary Data

In Go, a []byte slice stores raw binary data. When attempting to encode a struct containing []byte fields into JSON using json.Marshal(), the resulting JSON contains an unexpected string representation of the slice contents instead of the original binary data. For example:

<code class="go">type Msg struct {
    Content []byte
}

func main() {
    msg := Msg{[]byte("Hello")}
    json, _ := json.Marshal(msg)
    fmt.Println(string(json)) // Prints {"Content":"SGVsbG8="}
}</code>

Reason for Base64 Encoding

json.Marshal() encodes []byte slices as base64-encoded strings because JSON does not have a native representation for raw bytes. Base64 encoding represents binary data using a sequence of printable ASCII characters.

Solution: Recovering Original Binary Data

To retrieve the original binary data from the base64-encoded string in the JSON, simply decode the string using the base64.StdEncoding.DecodeString function:

<code class="go">import "encoding/base64"

func main() {
    ...
    decodedBytes, _ := base64.StdEncoding.DecodeString(msg.Content)
    fmt.Println(string(decodedBytes)) // Prints "Hello"
}</code>

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