feta: add globfs

Add a fs.FS impl to allow to filter an existing fs.FS by path patterns.

iox/globfs.go

@@ -0,0 +1,99 @@
+package iox
+
+import (
+	"io/fs"
+	"os"
+	"path"
+)
+
+type GlobFS struct {
+	base     fs.FS
+	patterns []string
+}
+
+// NewGlobFS creates a new GlobFS that exposes only files matching any of the given glob patterns.
+func NewGlobFS(base fs.FS, patterns ...string) *GlobFS {
+	return &GlobFS{base: base, patterns: patterns}
+}
+
+// match reports whether the given path matches any of the configured patterns.
+func (g *GlobFS) match(name string) bool {
+	for _, pat := range g.patterns {
+		if matched, _ := path.Match(pat, name); matched {
+			return true
+		}
+	}
+	return false
+}
+
+func (g *GlobFS) contains(dir string) bool {
+	queue := []string{dir}
+	visited := make(map[string]struct{})
+	for len(queue) > 0 {
+		current := queue[0]
+		queue = queue[1:] // dequeue
+
+		// Prevent visiting same dir multiple times
+		if _, seen := visited[current]; seen {
+			continue
+		}
+		visited[current] = struct{}{}
+
+		entries, err := fs.ReadDir(g.base, current)
+		if err != nil {
+			continue
+		}
+		for _, entry := range entries {
+			rel := path.Join(current, entry.Name())
+			if g.match(rel) {
+				return true
+			}
+			if entry.IsDir() {
+				queue = append(queue, rel)
+			}
+		}
+	}
+	return false
+}
+
+func (g *GlobFS) Open(name string) (fs.File, error) {
+	if g.match(name) {
+		return g.base.Open(name)
+	}
+
+	fi, err := fs.Stat(g.base, name)
+	if err != nil || !fi.IsDir() {
+		return nil, fs.ErrNotExist
+	}
+	if g.contains(name) {
+		return g.base.Open(name)
+	}
+	return nil, fs.ErrNotExist
+}
+
+func (g *GlobFS) ReadDir(name string) ([]fs.DirEntry, error) {
+	if g.match(name) {
+		return fs.ReadDir(g.base, name)
+	}
+
+	entries, err := fs.ReadDir(g.base, name)
+	if err != nil {
+		return nil, err
+	}
+	var children []fs.DirEntry
+	for _, entry := range entries {
+		rel := path.Join(name, entry.Name())
+		if g.match(rel) {
+			children = append(children, entry)
+		}
+		if entry.IsDir() && g.contains(rel) {
+			children = append(children, entry)
+		}
+	}
+
+	if len(children) == 0 {
+		return nil, os.ErrNotExist
+	}
+
+	return children, nil
+}