fix: abstract out cpio operations to helper function

This lets us defer the close operation to the end of the helper function
and not try to do the closes in all the early exit operations of the
loop.

Signed-off-by: Steve Beattie <steve.beattie@chainguard.dev>

Author: stevebeattie

pkg/archive/rpm.go

@@ -21,6 +21,47 @@ import (
 	"github.com/ulikunitz/xz"
 )
 
+// extractFileFromCPIO extracts a single file from a CPIO archive.
+func extractFileFromCPIO(ctx context.Context, cr *cpio.Reader, target string, buf []byte) error {
+	if err := os.MkdirAll(filepath.Dir(target), 0o700); err != nil {
+		return fmt.Errorf("failed to create parent directory: %w", err)
+	}
+
+	out, err := os.OpenFile(target, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0o600)
+	if err != nil {
+		return fmt.Errorf("failed to create file: %w", err)
+	}
+	defer out.Close()
+
+	var written int64
+	for {
+		if written > 0 && written%file.ExtractBuffer == 0 && ctx.Err() != nil {
+			return ctx.Err()
+		}
+
+		n, err := cr.Read(buf)
+		if n > 0 {
+			written += int64(n)
+			if written > file.MaxBytes {
+				return fmt.Errorf("file exceeds maximum allowed size (%d bytes): %s", file.MaxBytes, target)
+			}
+			if _, writeErr := out.Write(buf[:n]); writeErr != nil {
+				return fmt.Errorf("failed to write file contents: %w", writeErr)
+			}
+		}
+
+		if errors.Is(err, io.EOF) {
+			break
+		}
+
+		if err != nil {
+			return fmt.Errorf("failed to read file contents: %w", err)
+		}
+	}
+
+	return nil
+}
+
 // extractRPM extracts .rpm packages.
 //
 //nolint:cyclop // ignore complexity of 40
@@ -142,43 +183,8 @@ func ExtractRPM(ctx context.Context, d, f string) error {
 			continue
 		}
 
-		if err := os.MkdirAll(filepath.Dir(target), 0o700); err != nil {
-			return fmt.Errorf("failed to create parent directory: %w", err)
-		}
-
-		out, err := os.OpenFile(target, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0o600)
-		if err != nil {
-			return fmt.Errorf("failed to create file: %w", err)
-		}
-
-		var written int64
-		for {
-			if written > 0 && written%file.ExtractBuffer == 0 && ctx.Err() != nil {
-				return ctx.Err()
-			}
-
-			n, err := cr.Read(buf)
-			if n > 0 {
-				written += int64(n)
-				if written > file.MaxBytes {
-					return fmt.Errorf("file exceeds maximum allowed size (%d bytes): %s", file.MaxBytes, target)
-				}
-				if _, writeErr := out.Write(buf[:n]); writeErr != nil {
-					return fmt.Errorf("failed to write file contents: %w", writeErr)
-				}
-			}
-
-			if errors.Is(err, io.EOF) {
-				break
-			}
-
-			if err != nil {
-				return fmt.Errorf("failed to read file contents: %w", err)
-			}
-		}
-
-		if err := out.Close(); err != nil {
-			return fmt.Errorf("failed to close file: %w", err)
+		if err := extractFileFromCPIO(ctx, cr, target, buf); err != nil {
+			return err
 		}
 	}