EscapeHTML=false doesn't work

[teou]

set EscapeHTML=false but the following test doesn't work:

package main

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

        jsoniter "github.com/json-iterator/go"
)

var marshalConfig = jsoniter.Config{
        EscapeHTML:             false,
        SortMapKeys:            true,
        ValidateJsonRawMessage: true,
}.Froze()

type Foo struct {
        Bar interface{}
}

func (f *Foo) MarshalJSON() ([]byte, error) {
        ret, err := marshalConfig.Marshal(&f.Bar)
        fmt.Println("MarshalJSON ret", string(ret), err)
        return ret, err
}

func TestFooEncode(t *testing.T) {
        foo := &Foo{
                Bar: []string{"123<ab>", "ooo"},
        }
        out, err := marshalConfig.Marshal(foo)
        if err != nil {
                t.Error("err must be nil")
                return
        }

        var stdbuf bytes.Buffer
        stdenc := json.NewEncoder(&stdbuf)
        stdenc.SetEscapeHTML(false)
        stdenc.Encode(foo)

        stdout := string(stdbuf.Bytes())
        if stdout[len(stdout)-1:] == "\n" {
                stdout = stdout[:len(stdout)-1]
        }
        bufout := string(out)
        fmt.Println("stdout", stdout)
        fmt.Println("bufout", bufout)
        if stdout != bufout {
                t.Error(fmt.Sprintf("should equal,std=%v,buf=%v", stdout, bufout))
        }
}

the output is :

MarshalJSON ret ["123<ab>","ooo"] <nil>
MarshalJSON ret ["123<ab>","ooo"] <nil>
stdout ["123<ab>","ooo"]
bufout ["123\u003cab\u003e","ooo"]
--- FAIL: TestFooEncode (0.00s)
    fail_test.go:52: should equal,std=["123<ab>","ooo"],buf=["123\u003cab\u003e","ooo"]
FAIL
exit status 1

we can see that the json was correctly marshaled in Foo.MarshalJSON, but then escaped again by standard json package?

i think pull request #337 may caused this issue.

[teou]

@taowen