How to Marshal a []byte Field as a String in Go JSON Encoding?

Marshaling JSON []byte as Strings in Go

When encoding a struct containing []byte fields into JSON, an unexpected string representation may result. In this encoding, the []byte field is marshaled as a base64-encoded string, as stated in the documentation:

"Array and slice values encode as JSON arrays, except that []byte encodes as a base64-encoded string, and a nil slice encodes as the null JSON object."

To illustrate this behavior, consider the following Msg struct:

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

In the following example, the string "Hello" is converted to a []byte slice helloSlc and assigned to the Content field of the obj Msg object:

<code class="go">helloStr := "Hello"
helloSlc := []byte(helloStr)
obj := Msg{helloSlc}</code>

Upon encoding obj to JSON using json.Marshal, the resulting JSON contains the base64-encoded string representation of the []byte field:

<code class="go">json, _ := json.Marshal(obj)
fmt.Println(string(json))</code>

Output:

{"Content":"SGVsbG8="}

To obtain the original string value "Hello" in the JSON output, the []byte field needs to be explicitly decoded from its base64-encoded representation before encoding to JSON. This can be achieved using the encoding/base64 package:

<code class="go">import (
    "encoding/base64"
    "encoding/json"
    "fmt"
)

type Msg struct {
    Content string
}

func main() {
    helloSlc := []byte("Hello")
    obj := Msg{string(base64.StdEncoding.EncodeToString(helloSlc))}
    json, _ := json.Marshal(obj)
    fmt.Println(string(json))
}</code>

Output:

{"Content":"Hello"}

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