golang - json HTML escaping

Question

Attempting to use a custom MarshalJSON to avoid escaping characters like &. It's inconvenient to use a custom encoder with the SetEscapeHTML option set in this particular case.

The function is called, and behaves as I expected. However the end result still contains the escaped form \u0026.

https://play.golang.org/p/aktPndOUmth

package main

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

type Data struct {
    URL string
}

func (d Data) MarshalJSON() ([]byte, error) {

    data := map[string]interface{}{
        "url": d.URL,
    }

    jsonData, _ := json.Marshal(data)

    jsonData = bytes.Replace(jsonData, []byte("\\u0026"), []byte("&"), -1)

    fmt.Println("func: " + string(jsonData))

    return jsonData, nil
}

func main() {

    data := Data{
        URL: "https://test.com?foo=1&bar=2",
    }

    jsonData, _ := json.Marshal(data)

     fmt.Println("main: " + string(jsonData))
}

Output:

func: {"url":"https://test.com?foo=1&bar=2"}
main: {"url":"https://test.com?foo=1\u0026bar=2"}

json.Marshal specifically sets SetEscapeHTML to true. You have to use an encoder to set that yourself. You could always translate the characters after encoding. — Mr_Pink
– Mr_Pink, Commented Jan 5, 2018 at 17:08

Coconut · Accepted Answer · 2018-07-29 11:19:50Z

This is how I unescape sequences to make non-English letters in JSON to be readable. It will work as well for special characters like <, >, and &.

func _UnescapeUnicodeCharactersInJSON(_jsonRaw json.RawMessage) (json.RawMessage, error) {
    str, err := strconv.Unquote(strings.Replace(strconv.Quote(string(_jsonRaw)), `\\u`, `\u`, -1))
    if err != nil {
        return nil, err
    }
    return []byte(str), nil
}

func main() {
    // Both are valid JSON.
    var jsonRawEscaped json.RawMessage   // json raw with escaped unicode chars
    var jsonRawUnescaped json.RawMessage // json raw with unescaped unicode chars

    // '\u263a' == '☺'
    jsonRawEscaped = []byte(`{"HelloWorld": "\uC548\uB155, \uC138\uC0C1(\u4E16\u4E0A). \u263a"}`) // "\\u263a"
    jsonRawUnescaped, _ = _UnescapeUnicodeCharactersInJSON(jsonRawEscaped)                        // "☺"

    fmt.Println(string(jsonRawEscaped))   // {"HelloWorld": "\uC548\uB155, \uC138\uC0C1(\u4E16\u4E0A). \u263a"}
    fmt.Println(string(jsonRawUnescaped)) // {"HelloWorld": "안녕, 세상(世上). ☺"}
}

https://play.golang.org/p/pUsrzrrcDG-

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