fix(initrd): Ensure proper ordering and checks of (docker)files (#1964)

Reviewed-by: Cezar Craciunoiu <[email protected]>
Approved-by: Cezar Craciunoiu <[email protected]>

initrd/detect.go

@@ -12,11 +12,11 @@ import (
 // New attempts to return the builder for a supplied path which
 // will allow the provided ...
 func New(ctx context.Context, path string, opts ...InitrdOption) (Initrd, error) {
-	if builder, err := NewFromFile(ctx, path, opts...); err == nil {
+	if builder, err := NewFromDockerfile(ctx, path, opts...); err == nil {
 		return builder, nil
-	} else if builder, err := NewFromDirectory(ctx, path, opts...); err == nil {
+	} else if builder, err := NewFromFile(ctx, path, opts...); err == nil {
 		return builder, nil
-	} else if builder, err := NewFromDockerfile(ctx, path, opts...); err == nil {
+	} else if builder, err := NewFromDirectory(ctx, path, opts...); err == nil {
 		return builder, nil
 	} else if builder, err := NewFromOCIImage(ctx, path, opts...); err == nil {
 		return builder, nil

initrd/dockerfile.go

@@ -178,6 +178,13 @@ func NewFromDockerfile(ctx context.Context, path string, opts ...InitrdOption) (
 		return nil, fmt.Errorf("file is not a Dockerfile")
 	}
 
+	fi, err := os.Stat(path)
+	if err != nil {
+		return nil, fmt.Errorf("could not check Dockerfile: %w", err)
+	} else if fi.IsDir() {
+		return nil, fmt.Errorf("supplied path %s is a directory not a Dockerfile", path)
+	}
+
 	initrd := dockerfile{
 		opts: InitrdOptions{
 			workdir: filepath.Dir(path),