How to close a file after opening the file and creating a NewReader in another function?

Question

I want the func OpenFile() to read gzip files and bzip2 files. I will add other types later.

func OpenFile(name string) io.Reader{

  file, err := os.Open(name)

  if err != nil {
   log.Fatal(err)
 }

  if(strings.Contains(name, ".gz")){

    gzip, gerr := gzip.NewReader(file)
    if gerr != nil {
        log.Fatal(gerr)
    }
    return gzip

  }else if(strings.Contains(name, ".bz2")){

    bzip2 := bzip2.NewReader(file)
    return bzip2    

  }else{
    return file     
  } 
}

I call the OpenFile() in another function A:

    in := OpenFile(p)

    for _, d := range fdb.Detect(in) {
        set[d] = true
        counter++
    }
    ...

My issue is that if I use "defer file.Close()" in OpenFile(), the file would be closed too early so I can't get any input value. How can I close the file in A?

Notice that the gzip.NewReader(file) and the bzip2.NewReader(file) return different interfaces.

gzip: func NewReader(r io.Reader) (*Reader, error) // Reader has a func Close()

bzip2: func NewReader(r io.Reader) io.Reader // io.Reader doesn't have a func Close()

This is the reason that I can't return NewReader(file) in the first place.

Thank you!

Answer 1

As others have mentioned, you should return an io.ReadCloser from your function. Since the return value of bzip2.NewReader() does not satisfy io.ReadCloser, you'll need to create your own type.

type myFileType struct {
    io.Reader
    io.Closer
}

func OpenFile(name string) io.ReadCloser {

    file, err := os.Open(name)

    if err != nil {
        log.Fatal(err)
    }

    if strings.Contains(name, ".gz") {

        gzip, gerr := gzip.NewReader(file)
        if gerr != nil {
            log.Fatal(gerr)
        }
        return gzip

    } else if strings.Contains(name, ".bz2") {

        bzip2 := bzip2.NewReader(file)
        return myFileType{bzip2, file}

    } else {
        return file
    }
}