Plugins: Add Plugin FS abstraction (#63734)

* unexport pluginDir from dto

* first pass

* tidy

* naming + add mutex

* add dupe checking

* fix func typo

* interface + move logic from renderer

* remote finder

* remote signing

* fix tests

* tidy up

* tidy markdown logic

* split changes

* fix tests

* slim interface down

* fix status code

* tidy exec path func

* fixup

* undo changes

* remove unused func

* remove unused func

* fix goimports

* fetch remotely

* simultaneous support

* fix linter

* use var

* add exception for gosec warning

* fixup

* fix tests

* tidy

* rework cfg pattern

* simplify

* PR feedback

* fix dupe field

* remove g304 nolint

* apply PR feedback

* remove unnecessary gosec nolint

* fix finder loop and update comment

* fix map alloc

* fix test

* remove commented code

pkg/plugins/localfiles.go

@@ -0,0 +1,91 @@
+package plugins
+
+import (
+	"io/fs"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/grafana/grafana/pkg/util"
+)
+
+var _ fs.FS = (*LocalFS)(nil)
+
+type LocalFS struct {
+	m        map[string]*LocalFile
+	basePath string
+}
+
+func NewLocalFS(m map[string]struct{}, basePath string) LocalFS {
+	pfs := make(map[string]*LocalFile, len(m))
+	for k := range m {
+		pfs[k] = &LocalFile{
+			path: k,
+		}
+	}
+
+	return LocalFS{
+		m:        pfs,
+		basePath: basePath,
+	}
+}
+
+func (f LocalFS) Open(name string) (fs.File, error) {
+	cleanPath, err := util.CleanRelativePath(name)
+	if err != nil {
+		return nil, err
+	}
+
+	if kv, exists := f.m[filepath.Join(f.basePath, cleanPath)]; exists {
+		if kv.f != nil {
+			return kv.f, nil
+		}
+		return os.Open(kv.path)
+	}
+	return nil, ErrFileNotExist
+}
+
+func (f LocalFS) Base() string {
+	return f.basePath
+}
+
+func (f LocalFS) Files() []string {
+	var files []string
+	for p := range f.m {
+		r, err := filepath.Rel(f.basePath, p)
+		if strings.Contains(r, "..") || err != nil {
+			continue
+		}
+		files = append(files, r)
+	}
+
+	return files
+}
+
+var _ fs.File = (*LocalFile)(nil)
+
+type LocalFile struct {
+	f    *os.File
+	path string
+}
+
+func (p *LocalFile) Stat() (fs.FileInfo, error) {
+	return os.Stat(p.path)
+}
+
+func (p *LocalFile) Read(bytes []byte) (int, error) {
+	var err error
+	p.f, err = os.Open(p.path)
+	if err != nil {
+		return 0, err
+	}
+	return p.f.Read(bytes)
+}
+
+func (p *LocalFile) Close() error {
+	if p.f != nil {
+		return p.f.Close()
+	}
+	p.f = nil
+	return nil
+}