107 lines
2.0 KiB
Go
107 lines
2.0 KiB
Go
package overlay
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import (
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"io/fs"
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"os"
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"path"
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)
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// Interface guard
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// fs.ReadFileFS also fulfills fs.FS
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var _ fs.ReadFileFS = (*FS)(nil)
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// FS is an overlay File System
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type FS struct {
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fs fs.FS
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root string
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doCache bool
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cache map[string]bool
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}
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func (f *FS) apn(name string) string {
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return path.Join(f.root, name)
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}
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func (f *FS) exists(name string) bool {
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if has, ok := f.cache[name]; ok && f.doCache {
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return has
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}
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_, err := os.Stat(f.apn(name))
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if err != nil {
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f.cache[name] = false
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return false
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}
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f.cache[name] = true
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return true
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}
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// Open opens an fs.File, preferring disk
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func (f *FS) Open(name string) (fs.File, error) {
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if f.exists(name) {
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return os.Open(f.apn(name))
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}
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return f.fs.Open(name)
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}
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// ReadFile reads a file, preferring disk
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func (f *FS) ReadFile(name string) ([]byte, error) {
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if f.exists(name) {
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return os.ReadFile(f.apn(name))
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}
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return fs.ReadFile(f.fs, name)
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}
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// ReadDir reads []fs.DirEntry
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// This method will prefer EMBEDDED, because that is the "real" FS for overlay
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func (f *FS) ReadDir(name string) ([]fs.DirEntry, error) {
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return fs.ReadDir(f.fs, name)
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}
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// Option is a functional option for an FS
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type Option func(*FS) error
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// New returns a new FS
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func New(root string, fs fs.FS, opts ...Option) (*FS, error) {
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x := &FS{
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fs: fs,
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root: root,
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doCache: true,
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cache: make(map[string]bool),
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}
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for _, opt := range opts {
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if err := opt(x); err != nil {
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return x, err
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}
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}
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return x, nil
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}
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// MustNew returns New and panics on error
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func MustNew(root string, fs fs.FS, opts ...Option) *FS {
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f, err := New(root, fs, opts...)
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if err != nil {
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panic(err)
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}
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return f
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}
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// WithSub sets a fs.Sub for an FS
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func WithSub(sub string) Option {
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return func(x *FS) (err error) {
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x.fs, err = fs.Sub(x.fs, sub)
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return
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}
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}
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// WithCaching sets a caching mode for an FS
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// Caching avoids subsequent os.Stat to determine if a file exists on disk
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// See bench.txt for differences in usage
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func WithCaching(doCache bool) Option {
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return func(x *FS) error {
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x.doCache = doCache
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return nil
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}
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}
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