Initial DDC release

internal/extract/writer.go

@@ -0,0 +1,106 @@
+package extract
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+type entryWriter struct {
+	ctx      context.Context
+	root     string
+	limits   Limits
+	progress Progress
+	written  int64
+	entries  int
+}
+
+func (writer *entryWriter) writeDirectory(name string) error {
+	target, err := writer.prepare(name)
+	if err != nil || target == "" {
+		return err
+	}
+	return os.MkdirAll(target, 0o755)
+}
+
+func (writer *entryWriter) writeFile(name string, content io.Reader) error {
+	target, err := writer.prepare(name)
+	if err != nil || target == "" {
+		return err
+	}
+	if err := os.MkdirAll(filepath.Dir(target), 0o755); err != nil {
+		return err
+	}
+
+	file, err := os.OpenFile(target, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0o644)
+	if err != nil {
+		return err
+	}
+
+	remaining := writer.limits.MaxBytes - writer.written
+	source := &progressReader{ctx: writer.ctx, reader: io.LimitReader(content, remaining+1), progress: writer.progress}
+	copied, copyErr := io.Copy(file, source)
+	closeErr := file.Close()
+	writer.written += copied
+
+	if copyErr != nil {
+		return copyErr
+	}
+	if writer.written > writer.limits.MaxBytes {
+		return ErrTooLarge
+	}
+	return closeErr
+}
+
+func (writer *entryWriter) prepare(name string) (string, error) {
+	writer.entries++
+	if writer.entries > writer.limits.MaxEntries {
+		return "", ErrTooManyEntries
+	}
+	if err := writer.ctx.Err(); err != nil {
+		return "", err
+	}
+	return writer.resolve(name)
+}
+
+func (writer *entryWriter) resolve(name string) (string, error) {
+	normalized := strings.ReplaceAll(name, "\\", "/")
+	if strings.HasPrefix(normalized, "/") {
+		return "", fmt.Errorf("%w: %s", ErrUnsafeEntry, name)
+	}
+
+	cleaned := filepath.Clean(filepath.FromSlash(normalized))
+	if cleaned == "." {
+		return "", nil
+	}
+	if !filepath.IsLocal(cleaned) {
+		return "", fmt.Errorf("%w: %s", ErrUnsafeEntry, name)
+	}
+
+	target := filepath.Join(writer.root, cleaned)
+	relative, err := filepath.Rel(writer.root, target)
+	if err != nil || !filepath.IsLocal(relative) {
+		return "", fmt.Errorf("%w: %s", ErrUnsafeEntry, name)
+	}
+	return target, nil
+}
+
+type progressReader struct {
+	ctx      context.Context
+	reader   io.Reader
+	progress Progress
+}
+
+func (reader *progressReader) Read(buffer []byte) (int, error) {
+	if err := reader.ctx.Err(); err != nil {
+		return 0, err
+	}
+	count, err := reader.reader.Read(buffer)
+	if count > 0 {
+		reader.progress.Add(int64(count))
+	}
+	return count, err
+}