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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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