Wrapping a `fs.FS` in my own implementation of `fs.FS` makes `fs.Glob()` return no matches-CodePudding

I embed some files in my application and access them using a embed.FS. At some point I use fs.Glob(embedFS, ...) in my code. Everything is working as expected. Now I have the requirement to replace newlines with whitespaces before proceeding to process a files contents. I could read the whole file and do something like bytes.ReplaceAll(...) but I wanted to make this a bit nicer and not inflict the requirement of doing the replacement when working with my package (although I could hide that from the user). I decided to implement a wrapper around fs.FS (and fs.File) that deals with the replacing while reading the file. But my implementation breaks fs.Glob() as it does not return any matches:

type noLineBreakFile struct {
    file fs.File
}

func (f *noLineBreakFile) Stat() (fs.FileInfo, error) {
    return f.file.Stat()
}

func (f *noLineBreakFile) Read(p []byte) (n int, err error) {
    n, err = f.file.Read(p)
    pp := bytes.ReplaceAll(p, []byte{'\n'}, []byte{' '})
    copy(p, pp)
    return
}

func (f *noLineBreakFile) Close() error {
    return f.file.Close()
}

type noLineBreakFS struct {
    fs fs.FS
}

func (fs *noLineBreakFS) Open(name string) (fs.File, error) {
    f, err := fs.fs.Open(name)
    if err != nil {
        return nil, err
    }
    return &noLineBreakFile{f}, nil // <- returning f without the wrapper works fine
}

//go:embed *.tmpl
var embedFS embed.FS

func main() {
    matches, err := fs.Glob(embedFS) // Works fine ...
    fmt.Println(matches, err)

    matches, err = fs.Glob(&noLineBreakFS{embedFS}) // No matches!
    fmt.Println(matches, err)
}

What is the problem with my implementation of fs.File (noLineBreakFile)?

CodePudding user response：

Implement ReadDirFile so that Glob can read the directory entries.

func (nfs *noLineBreakFS) ReadDir(name string) ([]fs.DirEntry, error) {
    return fs.ReadDir(nfs.fs, name)
}