dis: Rework styling and build procedure

pkg/fsx/filter.go

@@ -0,0 +1,94 @@
+package fsx
+
+import (
+	"io/fs"
+	"path/filepath"
+
+	"github.com/tkw1536/goprogram/lib/collection"
+)
+
+// Censor returns a new filesystem censors files for which the censor function returns true.
+//
+// A censored file cannot be opened by the filesystem and return [fs.ErrNotExist].
+// Hard and Soft Links pointing to the file might still read it.
+func Censor(fsys fs.FS, censor func(name string) bool) fs.FS {
+	return &censorFS{
+		fsys:   fsys,
+		censor: censor,
+	}
+}
+
+type censorFS struct {
+	censor func(path string) bool
+	fsys   fs.FS
+}
+
+func (cf *censorFS) Sub(path string) (fs.FS, error) {
+	sub, err := fs.Sub(cf.fsys, path)
+	if err != nil {
+		return nil, err
+	}
+	return &censorFS{
+		censor: func(name string) bool {
+			return cf.censor(filepath.Join(path, name))
+		},
+		fsys: sub,
+	}, nil
+}
+
+func (ef *censorFS) Open(name string) (fs.File, error) {
+	if ef.censor(name) {
+		return nil, fs.ErrNotExist
+	}
+
+	file, err := ef.fsys.Open(name)
+
+	// we need to also censor the ReadDir function of the returned file
+	// this is to prevent the file from appearing in directory listings.
+	if rdf, ok := file.(fs.ReadDirFile); ok {
+		return &censorFSFile{
+			ReadDirFile: rdf,
+
+			name:   name,
+			censor: ef,
+		}, err
+	}
+	return file, err
+}
+
+type censorFSFile struct {
+	fs.ReadDirFile
+
+	name   string
+	censor *censorFS
+}
+
+func (f *censorFSFile) ReadDir(n int) ([]fs.DirEntry, error) {
+	entries, err := f.ReadDirFile.ReadDir(n)
+	return f.censor.handleReadDir(f.name, entries, err)
+}
+
+func (ef *censorFS) ReadDir(name string) ([]fs.DirEntry, error) {
+	if ef.censor(name) {
+		return nil, fs.ErrNotExist
+	}
+
+	// censor ReadDir() entries too
+	entries, err := fs.ReadDir(ef.fsys, name)
+	return ef.handleReadDir(name, entries, err)
+}
+
+// handleReadDir censors a ReadDir call
+func (ef *censorFS) handleReadDir(base string, entries []fs.DirEntry, err error) ([]fs.DirEntry, error) {
+	entries = collection.Filter(entries, func(entry fs.DirEntry) bool {
+		return !ef.censor(filepath.Join(base, entry.Name()))
+	})
+	return entries, err
+}
+
+func (ef *censorFS) ReadFile(name string) ([]byte, error) {
+	if ef.censor(name) {
+		return nil, fs.ErrNotExist
+	}
+	return fs.ReadFile(ef.fsys, name)
+}