在golang中将[] byte变成“虚拟”文件对象的简单方法？

Question

I know there are Go libraries that create entire filesystems like VFS. But I only want to make a byte array into something that can fulfil the File interface.

Answer 1

There is no ready solution for this in the standard library, but it's not that hard to do it yourself.

What we need is this http.File interface:

type File interface {
        io.Closer
        io.Reader
        io.Seeker
        Readdir(count int) ([]os.FileInfo, error)
        Stat() (os.FileInfo, error)
}

Please note that we can utilize bytes.Reader to do the heavy task, as that alone implements io.Reader and io.Seeker. io.Closer can be a noop, and Readdir() may return nil, nil as we're mocking a file not a directory, its Readdir() won't even be called.

The "hardest" part is to mock Stat() to return a value that implements os.FileInfo.

Here's a simple mocked FileInfo:

type myFileInfo struct {
    name string
    data []byte
}

func (mif myFileInfo) Name() string       { return mif.name }
func (mif myFileInfo) Size() int64        { return int64(len(mif.data)) }
func (mif myFileInfo) Mode() os.FileMode  { return 0444 }        // Read for all
func (mif myFileInfo) ModTime() time.Time { return time.Time{} } // Return anything
func (mif myFileInfo) IsDir() bool        { return false }
func (mif myFileInfo) Sys() interface{}   { return nil }

And with that we have everything to create our mocked http.File:

type MyFile struct {
    *bytes.Reader
    mif myFileInfo
}

func (mf *MyFile) Close() error { return nil } // Noop, nothing to do

func (mf *MyFile) Readdir(count int) ([]os.FileInfo, error) {
    return nil, nil // We are not a directory but a single file
}

func (mf *MyFile) Stat() (os.FileInfo, error) {
    return mf.mif, nil
}

Example using it (try it on the Go Playground):

data := []byte{0, 1, 2, 3}

mf := &MyFile{
    Reader: bytes.NewReader(data),
    mif: myFileInfo{
        name: "somename.txt",
        data: data,
    },
}

var f http.File = mf
_ = f