// cloneFileSystem returns a new memory-backed file system whose root contains
// a copy of the directory dirname in the source file system srcFS. The copy
// is not recursive; directories under dirname are not copied.
//
// Changes to the resultant file system do not modify the source file system.
//
// For example, if srcFS contained:
// - /bar
// - /baz/0
// - /foo/x
// - /foo/y
// - /foo/z/A
// - /foo/z/B
// then calling cloneFileSystem(srcFS, "/foo") would result in a file system
// containing:
// - /x
// - /y
func cloneFileSystem(srcFS db.FileSystem, dirname string) (db.FileSystem, error) {
if len(dirname) == 0 || dirname[len(dirname)-1] != os.PathSeparator {
dirname += string(os.PathSeparator)
}
dstFS := memfs.New()
list, err := srcFS.List(dirname)
if err != nil {
return nil, err
}
for _, name := range list {
srcFile, err := srcFS.Open(dirname + name)
if err != nil {
return nil, err
}
stat, err := srcFile.Stat()
if err != nil {
return nil, err
}
if stat.IsDir() {
err = srcFile.Close()
if err != nil {
return nil, err
}
continue
}
data := make([]byte, stat.Size())
_, err = io.ReadFull(srcFile, data)
if err != nil {
return nil, err
}
err = srcFile.Close()
if err != nil {
return nil, err
}
dstFile, err := dstFS.Create(name)
if err != nil {
return nil, err
}
_, err = dstFile.Write(data)
if err != nil {
return nil, err
}
err = dstFile.Close()
if err != nil {
return nil, err
}
}
return dstFS, nil
}
