Why Does Go's `json.Marshal` Encode `[]byte` as a Base64 String?

Marshaling []byte to JSON

In Go, marshaling []byte to JSON differs slightly from other data types. Instead of directly encoding the bytes as an array, the JSON package encodes []byte as a base64-encoded string. This behavior is explicitly stated in the documentation for encoding/json:

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.

Base64-Encoded String Output

In your case, the output of json.Marshal(group) contains "AAAAAQID". This represents the base64 encoding of your []byte slice:

originalBytes := []byte{0, 0, 0, 1, 2, 3}
encodedString := base64.StdEncoding.EncodeToString(originalBytes)

fmt.Println(encodedString) // Output: AAAAAQID

Decoding Base64 Data

To retrieve the original []byte values from the encoded string, you can decode the base64 data:

decodedBytes, err := base64.StdEncoding.DecodeString("AAAAAQID")
if err != nil {
    // Handle error
}

fmt.Println(decodedBytes) // Output: [0 0 0 1 2 3]

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