如何将我的二维字符串切片转换为[] byte？

Question

I have created a 2d slices and populated it from backend database but as json.Unmarshal accepts only []byte as first parameter how can I typecast my 2d slice to []byte.

Here is the sample code for reference as I can't share internal code:

package main

import (
    "encoding/json"
    "fmt"
    "io/ioutil"
    "net/http"
)

//User sjd
type User struct {
    EmailList [][]string `json:"emailList"`
}

func listHandler(w http.ResponseWriter, r *http.Request) {
    reqBody, _ := ioutil.ReadAll(r.Body)
    var user User
    json.Unmarshal(reqBody, &user)
    el := user.EmailList 
    keys := make([][]string, 0)
    json.Unmarshal([]byte(el), &keys) //this line not working because []byte(el) not possible
    fmt.Println(keys)
    w.Header().Set("Content-Type", "application/json")
    w.WriteHeader(http.StatusOK)
    w.Write([]byte(el))//this line not working because []byte(el) not possible
}

func main() {
    http.HandleFunc("/", listHandler)
    http.ListenAndServe(":8080", nil)
}

Sample request:

{
    "emailList": [
        [
            "[e-mail]",
            "[e-mail]"
        ],
        [
            "[e-mail]",
            "[e-mail]"
        ]
    ]
}

Answer 1

Unmarshal JSON as []byte to user. Marshal user.EmailList to JSON as []byte. For example,

package main

import (
    "encoding/json"
    "fmt"
    "os"
)

type User struct {
    EmailList [][]string `json:"emailList"`
}

func main() {
    // rBody, err := ioutil.ReadAll(r.Body)
    rBody := []byte(`
{
    "emailList": [
        [
            "[e-mail]",
            "[e-mail]"
        ],
        [
            "[e-mail]",
            "[e-mail]"
        ]
    ]
}
    `)
    fmt.Println(string(rBody))

    var user User
    err := json.Unmarshal(rBody, &user)
    if err != nil {
        fmt.Fprintln(os.Stderr, err)
        return
    }
    fmt.Println(user.EmailList)

    wData, err := json.Marshal(user.EmailList) // wData is []byte
    if err != nil {
        fmt.Fprintln(os.Stderr, err)
        return
    }
    fmt.Println(wData) // wData is []byte
    fmt.Println(string(wData))
    // _, err = w.Write(wData)
}

Playground: https://play.golang.org/p/S3HWiTqz--B

Output:

{
    "emailList": [
        [
            "[e-mail]",
            "[e-mail]"
        ],
        [
            "[e-mail]",
            "[e-mail]"
        ]
    ]
}

[[[e-mail] [e-mail]] [[e-mail] [e-mail]]]
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[["[e-mail]","[e-mail]"],["[e-mail]","[e-mail]"]]