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// Package union offers a simple http.FileSystem that can unify multiple filesystems at various mount points.
package union
import (
"fmt"
"io"
"net/http"
"os"
"strings"
"time"
)
// New creates an union filesystem with the provided mapping of mount points to filesystems.
//
// Each mount point must be of form "/mydir". It must start with a '/', and contain a single directory name.
func New(mapping map[string]http.FileSystem) http.FileSystem {
u := &unionFS{
ns: make(map[string]http.FileSystem),
root: &dirInfo{
name: "/",
},
}
for mountPoint, fs := range mapping {
u.bind(mountPoint, fs)
}
return u
}
type unionFS struct {
ns map[string]http.FileSystem // Key is mount point, e.g., "/mydir".
root *dirInfo
}
// bind mounts fs at mountPoint.
// mountPoint must be of form "/mydir". It must start with a '/', and contain a single directory name.
func (u *unionFS) bind(mountPoint string, fs http.FileSystem) {
u.ns[mountPoint] = fs
u.root.entries = append(u.root.entries, &dirInfo{
name: mountPoint[1:],
})
}
// Open opens the named file.
func (u *unionFS) Open(path string) (http.File, error) {
// TODO: Maybe clean path?
if path == "/" {
return &dir{
dirInfo: u.root,
}, nil
}
for prefix, fs := range u.ns {
if path == prefix || strings.HasPrefix(path, prefix+"/") {
innerPath := path[len(prefix):]
if innerPath == "" {
innerPath = "/"
}
return fs.Open(innerPath)
}
}
return nil, &os.PathError{Op: "open", Path: path, Err: os.ErrNotExist}
}
// dirInfo is a static definition of a directory.
type dirInfo struct {
name string
entries []os.FileInfo
}
func (d *dirInfo) Read([]byte) (int, error) {
return 0, fmt.Errorf("cannot Read from directory %s", d.name)
}
func (d *dirInfo) Close() error { return nil }
func (d *dirInfo) Stat() (os.FileInfo, error) { return d, nil }
func (d *dirInfo) Name() string { return d.name }
func (d *dirInfo) Size() int64 { return 0 }
func (d *dirInfo) Mode() os.FileMode { return 0755 | os.ModeDir }
func (d *dirInfo) ModTime() time.Time { return time.Time{} } // Actual mod time is not computed because it's expensive and rarely needed.
func (d *dirInfo) IsDir() bool { return true }
func (d *dirInfo) Sys() interface{} { return nil }
// dir is an opened dir instance.
type dir struct {
*dirInfo
pos int // Position within entries for Seek and Readdir.
}
func (d *dir) Seek(offset int64, whence int) (int64, error) {
if offset == 0 && whence == io.SeekStart {
d.pos = 0
return 0, nil
}
return 0, fmt.Errorf("unsupported Seek in directory %s", d.dirInfo.name)
}
func (d *dir) Readdir(count int) ([]os.FileInfo, error) {
if d.pos >= len(d.dirInfo.entries) && count > 0 {
return nil, io.EOF
}
if count <= 0 || count > len(d.dirInfo.entries)-d.pos {
count = len(d.dirInfo.entries) - d.pos
}
e := d.dirInfo.entries[d.pos : d.pos+count]
d.pos += count
return e, nil
}
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