Add new package xio with WriteCloserStack

@kodawah raised the problem that xz.Writer.Close doesn't close the
underlying writer. Instead of changing the behavior of the Writer I
added WriteCloserStack in a new package to address the problem.

fixes: #61

Author: ulikunitz

TODO.md

@@ -86,6 +86,12 @@
 
 ## Log
 
+### 2025-08-20
+
+Release v0.5.13 addressed issue #61 regarding handling of multiple WriteClosers
+together. So I added a new package xio with a WriteCloserStack to address the
+issue.
+
 ### 2024-04-03
 
 Release v0.5.12 updates README.md and SECURITY.md to address the supply chain

cmd/gxz/version.go

@@ -1,3 +1,3 @@
 package main
 
-const version = "v0.5.11"
+const version = "v0.5.13"

cmd/xb/copyright.go

@@ -1,4 +1,4 @@
-// Copyright 2014-2022 Ulrich Kunitz. All rights reserved.
+// Copyright 2014-2025 Ulrich Kunitz. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
@@ -28,7 +28,7 @@ func crUsage(w io.Writer) {
 }
 
 const copyrightText = `
-Copyright 2014-2022 Ulrich Kunitz. All rights reserved.
+Copyright 2014-2025 Ulrich Kunitz. All rights reserved.
 Use of this source code is governed by a BSD-style
 license that can be found in the LICENSE file.
 `

cmd/xb/version.go

@@ -1,3 +1,3 @@
 package main
 
-const version = "v0.5.11"
+const version = "v0.5.13"

doc/relnotes/release-v0.5.13.md

@@ -0,0 +1,4 @@
+# Release Notes v0.5.13
+
+This release adds package xio to handle situations with multiple WriteClosers
+that were pointed out by @kodawah in issue #61.

xio/write_closer_stack.go

@@ -0,0 +1,56 @@
+// Copyright 2014-2025 Ulrich Kunitz. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package xio provides tools to handle I/O operations. It contains the
+// [WriteCloserStack] type supporting combining multiple WriterClosers as single
+// [io.WriteCloser].
+package xio
+
+import (
+	"errors"
+	"io"
+)
+
+// WriteCloserStack allows to support multiple WriteClosers to be handled as
+// single WriteCloser.
+type WriteCloserStack struct {
+	Stack []io.WriteCloser
+}
+
+// NewWriteCloserStack creates a new WriteCloserStack. It will have an an empty
+// stack.
+func NewWriteCloserStack() *WriteCloserStack {
+	return &WriteCloserStack{}
+}
+
+// Write writes data to the top WriteCloser in the stack. If the stack is empty
+// Write will always succeed.
+func (w *WriteCloserStack) Write(p []byte) (n int, err error) {
+	k := len(w.Stack)
+	if k == 0 {
+		return len(p), nil
+	}
+	return w.Stack[k-1].Write(p)
+}
+
+// Close closes all writers on the stack and combines the errors. It will clear
+// the stack.
+func (w *WriteCloserStack) Close() error {
+	var errs []error
+	for k := len(w.Stack) - 1; k >= 0; k-- {
+		err := w.Stack[k].Close()
+		errs = append(errs, err)
+	}
+	w.Stack = nil
+	return errors.Join(errs...)
+}
+
+// Push adds a new WriteCloser to the top of the stack. It panics if the
+// WriteCloser is nil.
+func (w *WriteCloserStack) Push(wc io.WriteCloser) {
+	if wc == nil {
+		panic("cannot push nil WriteCloser onto stack")
+	}
+	w.Stack = append(w.Stack, wc)
+}

xio/write_closer_stack_test.go

@@ -0,0 +1,42 @@
+// Copyright 2014-2025 Ulrich Kunitz. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package xio_test
+
+import (
+	"io"
+	"os"
+
+	"github.com/ulikunitz/xz"
+	"github.com/ulikunitz/xz/xio"
+)
+
+func ExampleWriteCloserStack() {
+	wcStack := xio.NewWriteCloserStack()
+	defer wcStack.Close()
+
+	f, err := os.CreateTemp("", "example_write_closer_stack-*.xz")
+	if err != nil {
+		panic(err)
+	}
+	wcStack.Push(f)
+
+	z, err := xz.NewWriter(f)
+	if err != nil {
+		panic(err)
+	}
+	wcStack.Push(z)
+
+	_, err = io.WriteString(wcStack, "The fox jumps over the lazy dog.\n")
+	if err != nil {
+		panic(err)
+	}
+
+	err = wcStack.Close()
+	if err != nil {
+		panic(err)
+	}
+
+	// Output:
+}