golang: Marshal []os.FileInfo into JSON - json

Question

Basically, what I want to achieve is to get the content of a directory via os.ReadDir() and then encode the result into json.
Directly doing json.Marshal() 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 os.FileInfo() is an interface and cannot be extended this way.
What's the best way to do this?

Answer 1

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))
}

Answer 2

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)
}