Contain prompt content paths within source roots

internal/promptdef/content_source.go

@@ -0,0 +1,98 @@
+package promptdef
+
+import (
+	"fmt"
+	"io/fs"
+	"os"
+	"path"
+	"path/filepath"
+	"strings"
+
+	"gitea.maximumdirect.net/eric/promptkit/internal/filecatalog"
+)
+
+type contentSourceRoot interface {
+	readContentFile(sourcePath string, contentFile string) (string, string, error)
+}
+
+type osContentSourceRoot struct {
+	root                string
+	sourcePathsRelative bool
+}
+
+func (r osContentSourceRoot) readContentFile(sourcePath string, contentFile string) (string, string, error) {
+	if strings.TrimSpace(contentFile) == "" {
+		return "", "", fmt.Errorf("path is required")
+	}
+	if filepath.IsAbs(contentFile) {
+		return "", "", fmt.Errorf("path %q must be relative", contentFile)
+	}
+
+	root, err := filepath.Abs(r.root)
+	if err != nil {
+		return "", "", fmt.Errorf("resolve source root %q: %w", r.root, err)
+	}
+	canonicalRoot, err := filepath.EvalSymlinks(root)
+	if err != nil {
+		return "", "", fmt.Errorf("resolve source root %q: %w", r.root, err)
+	}
+
+	promptPath := sourcePath
+	if r.sourcePathsRelative && !filepath.IsAbs(promptPath) {
+		promptPath = filepath.Join(root, filepath.FromSlash(promptPath))
+	} else {
+		promptPath, err = filepath.Abs(promptPath)
+		if err != nil {
+			return "", "", fmt.Errorf("resolve prompt source %q: %w", sourcePath, err)
+		}
+	}
+	resolvedPath := filepath.Clean(filepath.Join(filepath.Dir(promptPath), contentFile))
+	if !containsOSPath(root, resolvedPath) {
+		return "", "", fmt.Errorf("path %q escapes source root %q", contentFile, r.root)
+	}
+
+	canonicalPath, err := filepath.EvalSymlinks(resolvedPath)
+	if err != nil {
+		return "", "", err
+	}
+	if !containsOSPath(canonicalRoot, canonicalPath) {
+		return "", "", fmt.Errorf("path %q escapes source root %q", contentFile, r.root)
+	}
+
+	body, err := os.ReadFile(canonicalPath)
+	if err != nil {
+		return "", "", err
+	}
+	return string(body), resolvedPath, nil
+}
+
+type fsContentSourceRoot struct {
+	fsys fs.FS
+	root string
+}
+
+func (r fsContentSourceRoot) readContentFile(sourcePath string, contentFile string) (string, string, error) {
+	root := filecatalog.CleanFSRoot(r.root)
+	cleanSourcePath := path.Clean(sourcePath)
+	if cleanSourcePath == root {
+		root = path.Dir(root)
+	}
+
+	resolvedPath, _, err := filecatalog.ResolveFSPath(root, path.Dir(cleanSourcePath), contentFile)
+	if err != nil {
+		return "", "", err
+	}
+	body, err := fs.ReadFile(r.fsys, resolvedPath)
+	if err != nil {
+		return "", "", err
+	}
+	return string(body), resolvedPath, nil
+}
+
+func containsOSPath(root string, name string) bool {
+	relative, err := filepath.Rel(root, name)
+	if err != nil || filepath.IsAbs(relative) {
+		return false
+	}
+	return relative != ".." && !strings.HasPrefix(relative, ".."+string(filepath.Separator))
+}