import "github.com/db47h/ofs"
Package ofs provides a primitive overlay FileSystem compatible with go/http. It has some write support and transparent zip file access (read-only).
This was designed primarily to handle asset loading where we want transpartent support for patches and mods. For those looking for something more advanced, there's https://github.com/spf13/afero/.
For example, suppose we have an assets directory:
assets/
shaders/
basic.glsl
sprites/
gear.png
The application will be shipped as an executable along with the assets packaged in a single zip file assets.zip. We also want transparent modding support, so we use an overlay filesystem that will look for files in the mods/assets directory then fallback to the assets.zip archive:
var ovl ofs.Overlay
err := ovl.Add(false, "assets.zip", "mods")
shader, err := ovl.Open("assets/shaders/basic.glsl")
The file "assets/shaders/basic.glsl" will be looked up in "mods/assets/shaders/basic.glsl" then "assets/shaders/basic.glsl" within the assets.zip file.
One could also add a local cache directory on top of the overlay for all write operations:
// fallback to some temp dir if any of these fail
cache, err := os.UserCacheDir()
cache = filepath.Join(cache, "myApp")
err = os.MkDir(cache)
err = ovl.Add(true, cache)
Note that there is no support to remove files. However, the Overlay FileSystem does not cache any information, client code can therefore use regular os calls to remove files without interference with the overlay.
dir.go fs.go overlay.go zip.go
type Dir stringA Dir implements FileSystem using the native file system restricted to a specific directory tree.
While the FileSystem.Open method takes '/'-separated paths, a Dir's string value is an absolute path to a directory on the native file system, not a URL, so it is separated by filepath.Separator, which isn't necessarily '/'.
It behaves similarly to http.Dir, with the difference that the string value must be an absolute path and that ErrNotExist errors are not resolved to the first non-existing directory when Open or Create fails.
func (d Dir) Create(name string) (File, error)Create implements FileSystem.Create.
func (d Dir) Open(name string) (File, error)Open implements FileSystem.Open.
type File interface {
io.Closer
io.Reader
io.Writer
io.Seeker
Readdir(count int) ([]os.FileInfo, error)
Stat() (os.FileInfo, error)
}A File is returned by a FileSystem's Open or Create method.
The methods should behave the same as those on an *os.File.
type FileSystem interface {
Open(name string) (File, error)
Create(name string) (File, error)
}A FileSystem implements access to a collection of named files. The elements in a file path are separated by slash ('/', U+002F) characters, regardless of host operating system convention.
Directory names are always rooted at the toplevel of the filesystem. i.e. Open("foo") and Open("/foo").
type Overlay struct {
// If ResolveExecDir is true, Add will try to resolve non-absolute paths
// relative to the path of the executable before trying the current directory.
ResolveExecDir bool
// contains filtered or unexported fields
}Overlay is a primitive overlay FileSystem. Add directories or zip files to the overlay with the Add method.
func (o *Overlay) Add(mustExist bool, dirs ...string) errorAdd adds the named directories to the overlay. The last directory added takes precedence.
A dir can also be a zip archive. However, this will be a read-only FileSystem and any File returned by Open will be read-only and not seek-able.
While the FileSystem.Open method takes '/'-separated paths, dir string values are filenames on the native file system, so it is separated by filepath.Separator, which isn't necessarily '/'.
In order to allow client code to safely call os.Chdir without interference, Overlay only keeps track of absolute paths. When a directory is added to the overlay, non-absolute paths are resolved relative to the path of executable first if ResolveRelative, then in the current directory.
Add will silently ignore non-existing directories if mustExist is false, and Open and Create will never look for files in these.
func (o *Overlay) Create(name string) (File, error)Create implements FileSystem.Create.
func (o *Overlay) Open(name string) (File, error)Open implements FileSystem.Open.
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