golang: Marshal []os.FileInfo into JSON

Basically, what I want to achieve is to get the content of a directory via <code>os.ReadDir()</code> and then encode the result into json.

Directly doing <code>json.Marshal()</code> cause no exception but gave me an empty result.

So I tried this:

func (f *os.FileInfo) MarshalerJSON() ([]byte, error) {
    return f.Name(), nil
}

Then Go tells me that <code>os.FileInfo()</code> is an interface and cannot be extended this way.

What's the best way to do this?

Pack the data into a struct that can be serialized:

http://play.golang.org/p/qDeg2bfik_

type FileInfo struct {
	Name    string
	Size    int64
	Mode    os.FileMode
	ModTime time.Time
	IsDir   bool
}

func main() {
	dir, err := os.Open(".")
	if err != nil {
		log.Fatal(err)
	}
	entries, err := dir.Readdir(0)
	if err != nil {
		log.Fatal(err)
	}

	list := []FileInfo{}

	for _, entry := range entries {
		f := FileInfo{
			Name:    entry.Name(),
			Size:    entry.Size(),
			Mode:    entry.Mode(),
			ModTime: entry.ModTime(),
			IsDir:   entry.IsDir(),
		}
		list = append(list, f)
	}

	output, err := json.Marshal(list)
	if err != nil {
		log.Fatal(err)
	}
	log.Println(string(output))

}

Here is a different version that makes the usage seemingly simple. Though you cannot unmarshall it back to the object. This is only applicable if you are sending it to client-end or something.

http://play.golang.org/p/vmm3temCUn

Usage

output, err := json.Marshal(FileInfo{entry})	

output, err := json.Marshal(FileInfoList{entries})

Code

type FileInfo struct {
	os.FileInfo
}

func (f FileInfo) MarshalJSON() ([]byte, error) {
	return json.Marshal(map[string]interface{}{
		"Name":    f.Name(),
		"Size":    f.Size(),
		"Mode":    f.Mode(),
		"ModTime": f.ModTime(),
		"IsDir":   f.IsDir(),
	})
}

type FileInfoList struct {
	fileInfoList []os.FileInfo
}

//This is inefficient to call multiple times for the same struct
func (f FileInfoList) MarshalJSON() ([]byte, error) {
	fileInfoList := make([]FileInfo, 0, len(f.fileInfoList))
	for _, val := range f.fileInfoList {
		fileInfoList = append(fileInfoList, FileInfo{val})
	}

	return json.Marshal(fileInfoList)
}