From 74352e9b4d11c832fc822b627aba2c482a82047b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E6=BA=90=E6=96=87=E9=9B=A8?=
 <41315874+fumiama@users.noreply.github.com>
Date: Thu, 9 Feb 2023 14:29:32 +0800
Subject: [PATCH] feat: pack use io.Copy

---
 pack.go           | 41 +++++++++++++++++++++++------------------
 structdoc_test.go |  7 +++++--
 2 files changed, 28 insertions(+), 20 deletions(-)

diff --git a/pack.go b/pack.go
index 6801db3..2bbe513 100644
--- a/pack.go
+++ b/pack.go
@@ -2,8 +2,9 @@ package docxlib
 
 import (
 	"archive/zip"
-	"bytes"
 	"encoding/xml"
+	"io"
+	"os"
 )
 
 // This receives a zip file writer (word documents are a zip with multiple xml inside)
@@ -18,30 +19,24 @@ func (f *Docx) pack(zipWriter *zip.Writer) (err error) {
 		"word/styles.xml",
 		"[Content_Types].xml",
 	}
-	files := make(map[string][]byte, 64)
+	files := make(map[string]io.Reader, 64)
 
 	for _, name := range fileslst {
-		files[name], err = TEMP_XML_FS.ReadFile("xml/" + name)
+		files[name], err = TEMP_XML_FS.Open("xml/" + name)
 		if err != nil {
 			return
 		}
 	}
-	files["word/_rels/document.xml.rels"], err = marshal(f.DocRelation)
-	if err != nil {
-		return
-	}
-	files["word/document.xml"], err = marshal(f.Document)
-	if err != nil {
-		return
-	}
+	files["word/_rels/document.xml.rels"] = marshaller{data: f.DocRelation}
+	files["word/document.xml"] = marshaller{data: f.Document}
 
-	for path, data := range files {
+	for path, r := range files {
 		w, err := zipWriter.Create(path)
 		if err != nil {
 			return err
 		}
 
-		_, err = w.Write(data)
+		_, err = io.Copy(w, r)
 		if err != nil {
 			return err
 		}
@@ -50,13 +45,23 @@ func (f *Docx) pack(zipWriter *zip.Writer) (err error) {
 	return
 }
 
-func marshal(data interface{}) (out []byte, err error) {
-	buf := bytes.NewBuffer(make([]byte, 0, 1024))
-	buf.WriteString(xml.Header)
-	err = xml.NewEncoder(buf).Encode(data)
+type marshaller struct {
+	data interface{}
+	io.Reader
+	io.WriterTo
+}
+
+// Read is fake and is to trigger io.WriterTo
+func (m marshaller) Read(p []byte) (n int, err error) {
+	return 0, os.ErrInvalid
+}
+
+// WriteTo n is always 0 for we don't care that value
+func (m marshaller) WriteTo(w io.Writer) (n int64, err error) {
+	_, err = io.WriteString(w, xml.Header)
 	if err != nil {
 		return
 	}
-	out = buf.Bytes()
+	err = xml.NewEncoder(w).Encode(m.data)
 	return
 }
diff --git a/structdoc_test.go b/structdoc_test.go
index 1d8bb4e..9d56bfa 100644
--- a/structdoc_test.go
+++ b/structdoc_test.go
@@ -575,10 +575,13 @@ func TestMarshalDrawingStructure(t *testing.T) {
 	nextPara := w.AddParagraph()
 	nextPara.AddLink("google", `http://google.com`)
 
-	doc, err := marshal(w.Document)
+	f, err := os.Create("test.xml")
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, err = marshaller{data: w.Document}.WriteTo(f)
 	if err != nil {
 		t.Fatal(err)
 	}
-	os.WriteFile("test.xml", doc, 0644)
 	t.Fail()
 }