// Package filter offers an http.FileSystem wrapper with the ability to keep or skip files.
package filter
import (
"fmt"
"io"
"net/http"
"os"
pathpkg "path"
"time"
)
// Func is a selection function which is provided two arguments,
// its '/'-separated cleaned rooted absolute path (i.e., it always begins with "/"),
// and the os.FileInfo of the considered file.
//
// The path is cleaned via pathpkg.Clean("/" + path).
//
// For example, if the considered file is named "a" and it's inside a directory "dir",
// then the value of path will be "/dir/a".
type Func func(path string, fi os.FileInfo) bool
// Keep returns a filesystem that contains only those entries in source for which
// keep returns true.
func Keep(source http.FileSystem, keep Func) http.FileSystem {
return &filterFS{source: source, keep: keep}
}
// Skip returns a filesystem that contains everything in source, except entries
// for which skip returns true.
func Skip(source http.FileSystem, skip Func) http.FileSystem {
keep := func(path string, fi os.FileInfo) bool {
return !skip(path, fi)
}
return &filterFS{source: source, keep: keep}
}
type filterFS struct {
source http.FileSystem
keep Func // Keep entries that keep returns true for.
}
func (fs *filterFS) Open(path string) (http.File, error) {
f, err := fs.source.Open(path)
if err != nil {
return nil, err
}
fi, err := f.Stat()
if err != nil {
f.Close()
return nil, err
}
if !fs.keep(clean(path), fi) {
// Skip.
f.Close()
return nil, &os.PathError{Op: "open", Path: path, Err: os.ErrNotExist}
}
if !fi.IsDir() {
return f, nil
}
defer f.Close()
fis, err := f.Readdir(0)
if err != nil {
return nil, err
}
var entries []os.FileInfo
for _, fi := range fis {
if !fs.keep(clean(pathpkg.Join(path, fi.Name())), fi) {
// Skip.
continue
}
entries = append(entries, fi)
}
return &dir{
name: fi.Name(),
entries: entries,
modTime: fi.ModTime(),
}, nil
}
// clean turns a potentially relative path into an absolute one.
//
// This is needed to normalize path parameter for selection function.
func clean(path string) string {
return pathpkg.Clean("/" + path)
}
// dir is an opened dir instance.
type dir struct {
name string
modTime time.Time
entries []os.FileInfo
pos int // Position within entries for Seek and Readdir.
}
func (d *dir) Read([]byte) (int, error) {
return 0, fmt.Errorf("cannot Read from directory %s", d.name)
}
func (d *dir) Close() error { return nil }
func (d *dir) Stat() (os.FileInfo, error) { return d, nil }
func (d *dir) Name() string { return d.name }
func (d *dir) Size() int64 { return 0 }
func (d *dir) Mode() os.FileMode { return 0755 | os.ModeDir }
func (d *dir) ModTime() time.Time { return d.modTime }
func (d *dir) IsDir() bool { return true }
func (d *dir) Sys() interface{} { return nil }
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.name)
}
func (d *dir) Readdir(count int) ([]os.FileInfo, error) {
if d.pos >= len(d.entries) && count > 0 {
return nil, io.EOF
}
if count <= 0 || count > len(d.entries)-d.pos {
count = len(d.entries) - d.pos
}
e := d.entries[d.pos : d.pos+count]
d.pos += count
return e, nil
}
