Stream to Excel table (#530)

* Support all datatypes for StreamWriter

* Support setting styles with StreamWriter

**NOTE:** This is a breaking change. Values are now explicitly
passed as a []interface{} for simplicity. We also let styles to be
set at the same time.

* Create function to write stream into a table

* Write rows directly to buffer

Avoiding the xml.Encoder makes the streamer faster and use less
memory.

Using the included benchmark, the results went from:

> BenchmarkStreamWriter-4   514  2576155 ns/op  454918 B/op  6592 allocs/op

down to:

> BenchmarkStreamWriter-4  1614   777480 ns/op  147608 B/op  5570 allocs/op

* Use AddTable instead of SetTable

This requires reading the cells after they have been written,
which requires additional structure for the temp file.

As a bonus, we now efficiently allocate only one buffer when
reading the file back into memory, using the same approach
as ioutil.ReadFile.

* Use an exported Cell type to handle inline styles for StreamWriter

adjust.go

@@ -196,10 +196,14 @@ func (f *File) adjustAutoFilterHelper(dir adjustDirection, coordinates []int, nu
 // areaRefToCoordinates provides a function to convert area reference to a
 // pair of coordinates.
 func (f *File) areaRefToCoordinates(ref string) ([]int, error) {
-	coordinates := make([]int, 4)
 	rng := strings.Split(ref, ":")
-	firstCell := rng[0]
-	lastCell := rng[1]
+	return areaRangeToCoordinates(rng[0], rng[1])
+}
+
+// areaRangeToCoordinates provides a function to convert cell range to a
+// pair of coordinates.
+func areaRangeToCoordinates(firstCell, lastCell string) ([]int, error) {
+	coordinates := make([]int, 4)
 	var err error
 	coordinates[0], coordinates[1], err = CellNameToCoordinates(firstCell)
 	if err != nil {
@@ -209,6 +213,19 @@ func (f *File) areaRefToCoordinates(ref string) ([]int, error) {
 	return coordinates, err
 }
 
+func sortCoordinates(coordinates []int) error {
+	if len(coordinates) != 4 {
+		return errors.New("coordinates length must be 4")
+	}
+	if coordinates[2] < coordinates[0] {
+		coordinates[2], coordinates[0] = coordinates[0], coordinates[2]
+	}
+	if coordinates[3] < coordinates[1] {
+		coordinates[3], coordinates[1] = coordinates[1], coordinates[3]
+	}
+	return nil
+}
+
 // coordinatesToAreaRef provides a function to convert a pair of coordinates
 // to area reference.
 func (f *File) coordinatesToAreaRef(coordinates []int) (string, error) {

cell.go

@@ -83,7 +83,8 @@ func (f *File) SetCellValue(sheet, axis string, value interface{}) error {
 	case []byte:
 		err = f.SetCellStr(sheet, axis, string(v))
 	case time.Duration:
-		err = f.SetCellDefault(sheet, axis, strconv.FormatFloat(v.Seconds()/86400.0, 'f', -1, 32))
+		_, d := setCellDuration(v)
+		err = f.SetCellDefault(sheet, axis, d)
 		if err != nil {
 			return err
 		}
@@ -131,28 +132,50 @@ func (f *File) setCellIntFunc(sheet, axis string, value interface{}) error {
 // setCellTimeFunc provides a method to process time type of value for
 // SetCellValue.
 func (f *File) setCellTimeFunc(sheet, axis string, value time.Time) error {
-	excelTime, err := timeToExcelTime(value)
+	xlsx, err := f.workSheetReader(sheet)
 	if err != nil {
 		return err
 	}
-	if excelTime > 0 {
-		err = f.SetCellDefault(sheet, axis, strconv.FormatFloat(excelTime, 'f', -1, 64))
-		if err != nil {
-			return err
-		}
+	cellData, col, _, err := f.prepareCell(xlsx, sheet, axis)
+	if err != nil {
+		return err
+	}
+	cellData.S = f.prepareCellStyle(xlsx, col, cellData.S)
+
+	var isNum bool
+	cellData.T, cellData.V, isNum, err = setCellTime(value)
+	if err != nil {
+		return err
+	}
+	if isNum {
 		err = f.setDefaultTimeStyle(sheet, axis, 22)
 		if err != nil {
 			return err
 		}
-	} else {
-		err = f.SetCellStr(sheet, axis, value.Format(time.RFC3339Nano))
-		if err != nil {
-			return err
-		}
 	}
 	return err
 }
 
+func setCellTime(value time.Time) (t string, b string, isNum bool, err error) {
+	var excelTime float64
+	excelTime, err = timeToExcelTime(value)
+	if err != nil {
+		return
+	}
+	isNum = excelTime > 0
+	if isNum {
+		t, b = setCellDefault(strconv.FormatFloat(excelTime, 'f', -1, 64))
+	} else {
+		t, b = setCellDefault(value.Format(time.RFC3339Nano))
+	}
+	return
+}
+
+func setCellDuration(value time.Duration) (t string, v string) {
+	v = strconv.FormatFloat(value.Seconds()/86400.0, 'f', -1, 32)
+	return
+}
+
 // SetCellInt provides a function to set int type value of a cell by given
 // worksheet name, cell coordinates and cell value.
 func (f *File) SetCellInt(sheet, axis string, value int) error {
@@ -165,11 +188,15 @@ func (f *File) SetCellInt(sheet, axis string, value int) error {
 		return err
 	}
 	cellData.S = f.prepareCellStyle(xlsx, col, cellData.S)
-	cellData.T = ""
-	cellData.V = strconv.Itoa(value)
+	cellData.T, cellData.V = setCellInt(value)
 	return err
 }
 
+func setCellInt(value int) (t string, v string) {
+	v = strconv.Itoa(value)
+	return
+}
+
 // SetCellBool provides a function to set bool type value of a cell by given
 // worksheet name, cell name and cell value.
 func (f *File) SetCellBool(sheet, axis string, value bool) error {
@@ -182,13 +209,18 @@ func (f *File) SetCellBool(sheet, axis string, value bool) error {
 		return err
 	}
 	cellData.S = f.prepareCellStyle(xlsx, col, cellData.S)
-	cellData.T = "b"
+	cellData.T, cellData.V = setCellBool(value)
+	return err
+}
+
+func setCellBool(value bool) (t string, v string) {
+	t = "b"
 	if value {
-		cellData.V = "1"
+		v = "1"
 	} else {
-		cellData.V = "0"
+		v = "0"
 	}
-	return err
+	return
 }
 
 // SetCellFloat sets a floating point value into a cell. The prec parameter
@@ -210,11 +242,15 @@ func (f *File) SetCellFloat(sheet, axis string, value float64, prec, bitSize int
 		return err
 	}
 	cellData.S = f.prepareCellStyle(xlsx, col, cellData.S)
-	cellData.T = ""
-	cellData.V = strconv.FormatFloat(value, 'f', prec, bitSize)
+	cellData.T, cellData.V = setCellFloat(value, prec, bitSize)
 	return err
 }
 
+func setCellFloat(value float64, prec, bitSize int) (t string, v string) {
+	v = strconv.FormatFloat(value, 'f', prec, bitSize)
+	return
+}
+
 // SetCellStr provides a function to set string type value of a cell. Total
 // number of characters that a cell can contain 32767 characters.
 func (f *File) SetCellStr(sheet, axis, value string) error {
@@ -226,21 +262,25 @@ func (f *File) SetCellStr(sheet, axis, value string) error {
 	if err != nil {
 		return err
 	}
+	cellData.S = f.prepareCellStyle(xlsx, col, cellData.S)
+	cellData.T, cellData.V, cellData.XMLSpace = setCellStr(value)
+	return err
+}
+
+func setCellStr(value string) (t string, v string, ns xml.Attr) {
 	if len(value) > 32767 {
 		value = value[0:32767]
 	}
 	// Leading and ending space(s) character detection.
 	if len(value) > 0 && (value[0] == 32 || value[len(value)-1] == 32) {
-		cellData.XMLSpace = xml.Attr{
+		ns = xml.Attr{
 			Name:  xml.Name{Space: NameSpaceXML, Local: "space"},
 			Value: "preserve",
 		}
 	}
-
-	cellData.S = f.prepareCellStyle(xlsx, col, cellData.S)
-	cellData.T = "str"
-	cellData.V = value
-	return err
+	t = "str"
+	v = value
+	return
 }
 
 // SetCellDefault provides a function to set string type value of a cell as
@@ -255,11 +295,15 @@ func (f *File) SetCellDefault(sheet, axis, value string) error {
 		return err
 	}
 	cellData.S = f.prepareCellStyle(xlsx, col, cellData.S)
-	cellData.T = ""
-	cellData.V = value
+	cellData.T, cellData.V = setCellDefault(value)
 	return err
 }
 
+func setCellDefault(value string) (t string, v string) {
+	v = value
+	return
+}
+
 // GetCellFormula provides a function to get formula from cell by given
 // worksheet name and axis in XLSX file.
 func (f *File) GetCellFormula(sheet, axis string) (string, error) {

stream.go

@@ -12,20 +12,23 @@ package excelize
 import (
 	"bytes"
 	"encoding/xml"
-	"errors"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"os"
 	"reflect"
+	"strconv"
+	"strings"
+	"time"
 )
 
 // StreamWriter defined the type of stream writer.
 type StreamWriter struct {
-	tmpFile   *os.File
-	File      *File
-	Sheet     string
-	SheetID   int
-	SheetData bytes.Buffer
+	File       *File
+	Sheet      string
+	SheetID    int
+	rawData    bufferedWriter
+	tableParts string
 }
 
 // NewStreamWriter return stream writer struct by given worksheet name for
@@ -46,7 +49,7 @@ type StreamWriter struct {
 //            row[colID] = rand.Intn(640000)
 //        }
 //        cell, _ := excelize.CoordinatesToCellName(1, rowID)
-//        if err := streamWriter.SetRow(cell, &row); err != nil {
+//        if err := streamWriter.SetRow(cell, row, nil); err != nil {
 //            panic(err)
 //        }
 //    }
@@ -62,157 +65,433 @@ func (f *File) NewStreamWriter(sheet string) (*StreamWriter, error) {
 	if sheetID == 0 {
 		return nil, fmt.Errorf("sheet %s is not exist", sheet)
 	}
-	rsw := &StreamWriter{
+	sw := &StreamWriter{
 		File:    f,
 		Sheet:   sheet,
 		SheetID: sheetID,
 	}
-	rsw.SheetData.WriteString("<sheetData>")
-	return rsw, nil
+
+	ws, err := f.workSheetReader(sheet)
+	if err != nil {
+		return nil, err
+	}
+	sw.rawData.WriteString(XMLHeader + `<worksheet` + templateNamespaceIDMap)
+	bulkAppendOtherFields(&sw.rawData, ws, "XMLName", "SheetData", "TableParts")
+	sw.rawData.WriteString(`<sheetData>`)
+	return sw, nil
 }
 
-// SetRow writes an array to streaming row by given worksheet name, starting
-// coordinate and a pointer to array type 'slice'. Note that, cell settings
-// with styles are not supported currently and after set rows, you must call the
-// 'Flush' method to end the streaming writing process. The following
-// shows the supported data types:
+// AddTable creates an Excel table for the StreamWriter using the given
+// coordinate area and format set. For example, create a table of A1:D5:
 //
-//    int
-//    string
+//    err := sw.AddTable("A1", "D5", ``)
 //
-func (sw *StreamWriter) SetRow(axis string, slice interface{}) error {
-	col, row, err := CellNameToCoordinates(axis)
+// Create a table of F2:H6 with format set:
+//
+//    err := sw.AddTable("F2", "H6", `{"table_name":"table","table_style":"TableStyleMedium2","show_first_column":true,"show_last_column":true,"show_row_stripes":false,"show_column_stripes":true}`)
+//
+// Note that the table must be at least two lines including the header. The
+// header cells must contain strings and must be unique.
+//
+// Currently only one table is allowed for a StreamWriter. AddTable must be
+// called after the rows are written but before Flush.
+//
+// See File.AddTable for details on the table format.
+func (sw *StreamWriter) AddTable(hcell, vcell, format string) error {
+	formatSet, err := parseFormatTableSet(format)
 	if err != nil {
 		return err
 	}
-	// Make sure 'slice' is a Ptr to Slice
-	v := reflect.ValueOf(slice)
-	if v.Kind() != reflect.Ptr || v.Elem().Kind() != reflect.Slice {
-		return errors.New("pointer to slice expected")
+
+	coordinates, err := areaRangeToCoordinates(hcell, vcell)
+	if err != nil {
+		return err
 	}
-	v = v.Elem()
-	sw.SheetData.WriteString(fmt.Sprintf(`<row r="%d">`, row))
-	for i := 0; i < v.Len(); i++ {
-		axis, err := CoordinatesToCellName(col+i, row)
+	sortCoordinates(coordinates)
+
+	// Correct the minimum number of rows, the table at least two lines.
+	if coordinates[1] == coordinates[3] {
+		coordinates[3]++
+	}
+
+	// Correct table reference coordinate area, such correct C1:B3 to B1:C3.
+	ref, err := sw.File.coordinatesToAreaRef(coordinates)
+	if err != nil {
+		return err
+	}
+
+	// create table columns using the first row
+	tableHeaders, err := sw.getRowValues(coordinates[1], coordinates[0], coordinates[2])
+	if err != nil {
+		return err
+	}
+	tableColumn := make([]*xlsxTableColumn, len(tableHeaders))
+	for i, name := range tableHeaders {
+		tableColumn[i] = &xlsxTableColumn{
+			ID:   i + 1,
+			Name: name,
+		}
+	}
+
+	tableID := sw.File.countTables() + 1
+
+	name := formatSet.TableName
+	if name == "" {
+		name = "Table" + strconv.Itoa(tableID)
+	}
+
+	table := xlsxTable{
+		XMLNS:       NameSpaceSpreadSheet,
+		ID:          tableID,
+		Name:        name,
+		DisplayName: name,
+		Ref:         ref,
+		AutoFilter: &xlsxAutoFilter{
+			Ref: ref,
+		},
+		TableColumns: &xlsxTableColumns{
+			Count:       len(tableColumn),
+			TableColumn: tableColumn,
+		},
+		TableStyleInfo: &xlsxTableStyleInfo{
+			Name:              formatSet.TableStyle,
+			ShowFirstColumn:   formatSet.ShowFirstColumn,
+			ShowLastColumn:    formatSet.ShowLastColumn,
+			ShowRowStripes:    formatSet.ShowRowStripes,
+			ShowColumnStripes: formatSet.ShowColumnStripes,
+		},
+	}
+
+	sheetRelationshipsTableXML := "../tables/table" + strconv.Itoa(tableID) + ".xml"
+	tableXML := strings.Replace(sheetRelationshipsTableXML, "..", "xl", -1)
+
+	// Add first table for given sheet.
+	sheetPath, _ := sw.File.sheetMap[trimSheetName(sw.Sheet)]
+	sheetRels := "xl/worksheets/_rels/" + strings.TrimPrefix(sheetPath, "xl/worksheets/") + ".rels"
+	rID := sw.File.addRels(sheetRels, SourceRelationshipTable, sheetRelationshipsTableXML, "")
+
+	sw.tableParts = fmt.Sprintf(`<tableParts count="1"><tablePart r:id="rId%d"></tablePart></tableParts>`, rID)
+
+	sw.File.addContentTypePart(tableID, "table")
+
+	b, _ := xml.Marshal(table)
+	sw.File.saveFileList(tableXML, b)
+	return nil
+}
+
+// Extract values from a row in the StreamWriter.
+func (sw *StreamWriter) getRowValues(hrow, hcol, vcol int) (res []string, err error) {
+	res = make([]string, vcol-hcol+1)
+
+	r, err := sw.rawData.Reader()
+	if err != nil {
+		return nil, err
+	}
+
+	dec := xml.NewDecoder(r)
+	for {
+		token, err := dec.Token()
+		if err == io.EOF {
+			return res, nil
+		}
 		if err != nil {
-			return err
+			return nil, err
 		}
-		switch val := v.Index(i).Interface().(type) {
-		case int:
-			sw.SheetData.WriteString(fmt.Sprintf(`<c r="%s"><v>%d</v></c>`, axis, val))
-		case string:
-			sw.SheetData.WriteString(sw.setCellStr(axis, val))
-		default:
-			sw.SheetData.WriteString(sw.setCellStr(axis, fmt.Sprint(val)))
+		startElement, ok := getRowElement(token, hrow)
+		if !ok {
+			continue
 		}
-	}
-	sw.SheetData.WriteString(`</row>`)
-	// Try to use local storage
-	chunk := 1 << 24
-	if sw.SheetData.Len() >= chunk {
-		if sw.tmpFile == nil {
-			err := sw.createTmp()
+		// decode cells
+		var row xlsxRow
+		if err := dec.DecodeElement(&row, &startElement); err != nil {
+			return nil, err
+		}
+		for _, c := range row.C {
+			col, _, err := CellNameToCoordinates(c.R)
 			if err != nil {
-				// can not use local storage
-				return nil
+				return nil, err
 			}
+			if col < hcol || col > vcol {
+				continue
+			}
+			res[col-hcol] = c.V
 		}
-		// use local storage
-		_, err := sw.tmpFile.Write(sw.SheetData.Bytes())
-		if err != nil {
-			return nil
+		return res, nil
+	}
+}
+
+// Check if the token is an XLSX row with the matching row number.
+func getRowElement(token xml.Token, hrow int) (startElement xml.StartElement, ok bool) {
+	startElement, ok = token.(xml.StartElement)
+	if !ok {
+		return
+	}
+	ok = startElement.Name.Local == "row"
+	if !ok {
+		return
+	}
+	ok = false
+	for _, attr := range startElement.Attr {
+		if attr.Name.Local != "r" {
+			continue
+		}
+		row, _ := strconv.Atoi(attr.Value)
+		if row == hrow {
+			ok = true
+			return
 		}
-		sw.SheetData.Reset()
 	}
-	return err
+	return
 }
 
-// Flush ending the streaming writing process.
-func (sw *StreamWriter) Flush() error {
-	sw.SheetData.WriteString(`</sheetData>`)
+// Cell can be used directly in StreamWriter.SetRow to specify a style and
+// a value.
+type Cell struct {
+	StyleID int
+	Value interface{}
+}
 
-	ws, err := sw.File.workSheetReader(sw.Sheet)
+// SetRow writes an array to stream rows by giving a worksheet name, starting
+// coordinate and a pointer to an array of values. Note that you must call the
+// 'Flush' method to end the streaming writing process.
+//
+// As a special case, if Cell is used as a value, then the Cell.StyleID will be
+// applied to that cell.
+func (sw *StreamWriter) SetRow(axis string, values []interface{}) error {
+	col, row, err := CellNameToCoordinates(axis)
 	if err != nil {
 		return err
 	}
-	sheetXML := fmt.Sprintf("xl/worksheets/sheet%d.xml", sw.SheetID)
-	delete(sw.File.Sheet, sheetXML)
-	delete(sw.File.checked, sheetXML)
-	var sheetDataByte []byte
-	if sw.tmpFile != nil {
-		// close the local storage file
-		if err = sw.tmpFile.Close(); err != nil {
-			return err
-		}
 
-		file, err := os.Open(sw.tmpFile.Name())
+	fmt.Fprintf(&sw.rawData, `<row r="%d">`, row)
+	for i, val := range values {
+		axis, err := CoordinatesToCellName(col+i, row)
 		if err != nil {
 			return err
 		}
-
-		sheetDataByte, err = ioutil.ReadAll(file)
-		if err != nil {
-			return err
+		c := xlsxC{R: axis}
+		if v, ok := val.(Cell); ok {
+			c.S = v.StyleID
+			val = v.Value
+		} else if v, ok := val.(*Cell); ok && v != nil {
+			c.S = v.StyleID
+			val = v.Value
 		}
-
-		if err := file.Close(); err != nil {
-			return err
+		switch val := val.(type) {
+		case int:
+			c.T, c.V = setCellInt(val)
+		case int8:
+			c.T, c.V = setCellInt(int(val))
+		case int16:
+			c.T, c.V = setCellInt(int(val))
+		case int32:
+			c.T, c.V = setCellInt(int(val))
+		case int64:
+			c.T, c.V = setCellInt(int(val))
+		case uint:
+			c.T, c.V = setCellInt(int(val))
+		case uint8:
+			c.T, c.V = setCellInt(int(val))
+		case uint16:
+			c.T, c.V = setCellInt(int(val))
+		case uint32:
+			c.T, c.V = setCellInt(int(val))
+		case uint64:
+			c.T, c.V = setCellInt(int(val))
+		case float32:
+			c.T, c.V = setCellFloat(float64(val), -1, 32)
+		case float64:
+			c.T, c.V = setCellFloat(val, -1, 64)
+		case string:
+			c.T, c.V, c.XMLSpace = setCellStr(val)
+		case []byte:
+			c.T, c.V, c.XMLSpace = setCellStr(string(val))
+		case time.Duration:
+			c.T, c.V = setCellDuration(val)
+		case time.Time:
+			c.T, c.V, _, err = setCellTime(val)
+		case bool:
+			c.T, c.V = setCellBool(val)
+		case nil:
+			c.T, c.V, c.XMLSpace = setCellStr("")
+		default:
+			c.T, c.V, c.XMLSpace = setCellStr(fmt.Sprint(val))
 		}
-
-		err = os.Remove(sw.tmpFile.Name())
 		if err != nil {
 			return err
 		}
+		writeCell(&sw.rawData, c)
 	}
+	sw.rawData.WriteString(`</row>`)
+	return sw.rawData.Sync()
+}
 
-	sheetDataByte = append(sheetDataByte, sw.SheetData.Bytes()...)
-	replaceMap := map[string][]byte{
-		"XMLName":   {},
-		"SheetData": sheetDataByte,
+func writeCell(buf *bufferedWriter, c xlsxC) {
+	buf.WriteString(`<c`)
+	if c.XMLSpace.Value != "" {
+		fmt.Fprintf(buf, ` xml:%s="%s"`, c.XMLSpace.Name.Local, c.XMLSpace.Value)
 	}
-	sw.SheetData.Reset()
-	sw.File.XLSX[fmt.Sprintf("xl/worksheets/sheet%d.xml", sw.SheetID)] =
-		StreamMarshalSheet(ws, replaceMap)
-	return err
+	fmt.Fprintf(buf, ` r="%s"`, c.R)
+	if c.S != 0 {
+		fmt.Fprintf(buf, ` s="%d"`, c.S)
+	}
+	if c.T != "" {
+		fmt.Fprintf(buf, ` t="%s"`, c.T)
+	}
+	buf.WriteString(`>`)
+	if c.V != "" {
+		buf.WriteString(`<v>`)
+		xml.EscapeText(buf, []byte(c.V))
+		buf.WriteString(`</v>`)
+	}
+	buf.WriteString(`</c>`)
 }
 
-// createTmp creates a temporary file in the operating system default
-// temporary directory.
-func (sw *StreamWriter) createTmp() (err error) {
-	sw.tmpFile, err = ioutil.TempFile(os.TempDir(), "excelize-")
-	return err
+// Flush ending the streaming writing process.
+func (sw *StreamWriter) Flush() error {
+	sw.rawData.WriteString(`</sheetData>`)
+	sw.rawData.WriteString(sw.tableParts)
+	sw.rawData.WriteString(`</worksheet>`)
+	if err := sw.rawData.Flush(); err != nil {
+		return err
+	}
+
+	sheetXML := fmt.Sprintf("xl/worksheets/sheet%d.xml", sw.SheetID)
+	delete(sw.File.Sheet, sheetXML)
+	delete(sw.File.checked, sheetXML)
+
+	defer sw.rawData.Close()
+	b, err := sw.rawData.Bytes()
+	if err != nil {
+		return err
+	}
+	sw.File.XLSX[sheetXML] = b
+	return nil
 }
 
-// StreamMarshalSheet provides method to serialization worksheets by field as
-// streaming.
-func StreamMarshalSheet(ws *xlsxWorksheet, replaceMap map[string][]byte) []byte {
+// bulkAppendOtherFields bulk-appends fields in a worksheet, skipping the
+// specified field names.
+func bulkAppendOtherFields(w io.Writer, ws *xlsxWorksheet, skip ...string) {
+	skipMap := make(map[string]struct{})
+	for _, name := range skip {
+		skipMap[name] = struct{}{}
+	}
+
 	s := reflect.ValueOf(ws).Elem()
 	typeOfT := s.Type()
-	var marshalResult []byte
-	marshalResult = append(marshalResult, []byte(XMLHeader+`<worksheet`+templateNamespaceIDMap)...)
+	enc := xml.NewEncoder(w)
 	for i := 0; i < s.NumField(); i++ {
-		content, ok := replaceMap[typeOfT.Field(i).Name]
-		if ok {
-			marshalResult = append(marshalResult, content...)
+		f := s.Field(i)
+		if _, ok := skipMap[typeOfT.Field(i).Name]; ok {
 			continue
 		}
-		out, _ := xml.Marshal(s.Field(i).Interface())
-		marshalResult = append(marshalResult, out...)
+		enc.Encode(f.Interface())
 	}
-	marshalResult = append(marshalResult, []byte(`</worksheet>`)...)
-	return marshalResult
 }
 
-// setCellStr provides a function to set string type value of a cell as
-// streaming. Total number of characters that a cell can contain 32767
-// characters.
-func (sw *StreamWriter) setCellStr(axis, value string) string {
-	if len(value) > 32767 {
-		value = value[0:32767]
+// bufferedWriter uses a temp file to store an extended buffer. Writes are
+// always made to an in-memory buffer, which will always succeed. The buffer
+// is written to the temp file with Sync, which may return an error. Therefore,
+// Sync should be periodically called and the error checked.
+type bufferedWriter struct {
+	tmp *os.File
+	buf bytes.Buffer
+}
+
+// Write to the in-memory buffer. The err is always nil.
+func (bw *bufferedWriter) Write(p []byte) (n int, err error) {
+	return bw.buf.Write(p)
+}
+
+// WriteString wites to the in-memory buffer. The err is always nil.
+func (bw *bufferedWriter) WriteString(p string) (n int, err error) {
+	return bw.buf.WriteString(p)
+}
+
+// Reader provides read-access to the underlying buffer/file.
+func (bw *bufferedWriter) Reader() (io.Reader, error) {
+	if bw.tmp == nil {
+		return bytes.NewReader(bw.buf.Bytes()), nil
+	}
+	if err := bw.Flush(); err != nil {
+		return nil, err
+	}
+	fi, err := bw.tmp.Stat()
+	if err != nil {
+		return nil, err
 	}
-	// Leading and ending space(s) character detection.
-	if len(value) > 0 && (value[0] == 32 || value[len(value)-1] == 32) {
-		return fmt.Sprintf(`<c xml:space="preserve" r="%s" t="str"><v>%s</v></c>`, axis, value)
+	// os.File.ReadAt does not affect the cursor position and is safe to use here
+	return io.NewSectionReader(bw.tmp, 0, fi.Size()), nil
+}
+
+// Bytes returns the entire content of the bufferedWriter. If a temp file is
+// used, Bytes will efficiently allocate a buffer to prevent re-allocations.
+func (bw *bufferedWriter) Bytes() ([]byte, error) {
+	if bw.tmp == nil {
+		return bw.buf.Bytes(), nil
+	}
+
+	if err := bw.Flush(); err != nil {
+		return nil, err
+	}
+
+	var buf bytes.Buffer
+	if fi, err := bw.tmp.Stat(); err == nil {
+		if size := fi.Size() + bytes.MinRead; size > bytes.MinRead {
+			if int64(int(size)) == size {
+				buf.Grow(int(size))
+			} else {
+				return nil, bytes.ErrTooLarge
+			}
+		}
+	}
+
+	if _, err := bw.tmp.Seek(0, 0); err != nil {
+		return nil, err
+	}
+
+	_, err := buf.ReadFrom(bw.tmp)
+	return buf.Bytes(), err
+}
+
+// Sync will write the in-memory buffer to a temp file, if the in-memory buffer
+// has grown large enough. Any error will be returned.
+func (bw *bufferedWriter) Sync() (err error) {
+	// Try to use local storage
+	const chunk = 1 << 24
+	if bw.buf.Len() < chunk {
+		return nil
+	}
+	if bw.tmp == nil {
+		bw.tmp, err = ioutil.TempFile(os.TempDir(), "excelize-")
+		if err != nil {
+			// can not use local storage
+			return nil
+		}
+	}
+	return bw.Flush()
+}
+
+// Flush the entire in-memory buffer to the temp file, if a temp file is being
+// used.
+func (bw *bufferedWriter) Flush() error {
+	if bw.tmp == nil {
+		return nil
+	}
+	_, err := bw.buf.WriteTo(bw.tmp)
+	if err != nil {
+		return err
+	}
+	bw.buf.Reset()
+	return nil
+}
+
+// Close the underlying temp file and reset the in-memory buffer.
+func (bw *bufferedWriter) Close() error {
+	bw.buf.Reset()
+	if bw.tmp == nil {
+		return nil
 	}
-	return fmt.Sprintf(`<c r="%s" t="str"><v>%s</v></c>`, axis, value)
+	defer os.Remove(bw.tmp.Name())
+	return bw.tmp.Close()
 }

stream_test.go

 package excelize
 
 import (
+	"encoding/xml"
+	"fmt"
 	"math/rand"
 	"path/filepath"
 	"strings"
@@ -9,6 +11,25 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
+func BenchmarkStreamWriter(b *testing.B) {
+	file := NewFile()
+
+	row := make([]interface{}, 10)
+	for colID := 0; colID < 10; colID++ {
+		row[colID] = colID
+	}
+
+	for n := 0; n < b.N; n++ {
+		streamWriter, _ := file.NewStreamWriter("Sheet1")
+		for rowID := 10; rowID <= 110; rowID++ {
+			cell, _ := CoordinatesToCellName(1, rowID)
+			streamWriter.SetRow(cell, row)
+		}
+	}
+
+	b.ReportAllocs()
+}
+
 func TestStreamWriter(t *testing.T) {
 	file := NewFile()
 	streamWriter, err := file.NewStreamWriter("Sheet1")
@@ -17,16 +38,16 @@ func TestStreamWriter(t *testing.T) {
 	// Test max characters in a cell.
 	row := make([]interface{}, 1)
 	row[0] = strings.Repeat("c", 32769)
-	assert.NoError(t, streamWriter.SetRow("A1", &row))
+	assert.NoError(t, streamWriter.SetRow("A1", row))
 
 	// Test leading and ending space(s) character characters in a cell.
 	row = make([]interface{}, 1)
 	row[0] = " characters"
-	assert.NoError(t, streamWriter.SetRow("A2", &row))
+	assert.NoError(t, streamWriter.SetRow("A2", row))
 
 	row = make([]interface{}, 1)
 	row[0] = []byte("Word")
-	assert.NoError(t, streamWriter.SetRow("A3", &row))
+	assert.NoError(t, streamWriter.SetRow("A3", row))
 
 	for rowID := 10; rowID <= 51200; rowID++ {
 		row := make([]interface{}, 50)
@@ -34,26 +55,13 @@ func TestStreamWriter(t *testing.T) {
 			row[colID] = rand.Intn(640000)
 		}
 		cell, _ := CoordinatesToCellName(1, rowID)
-		assert.NoError(t, streamWriter.SetRow(cell, &row))
+		assert.NoError(t, streamWriter.SetRow(cell, row))
 	}
 
 	assert.NoError(t, streamWriter.Flush())
 	// Save xlsx file by the given path.
 	assert.NoError(t, file.SaveAs(filepath.Join("test", "TestStreamWriter.xlsx")))
 
-	// Test error exceptions
-	_, err = file.NewStreamWriter("SheetN")
-	assert.EqualError(t, err, "sheet SheetN is not exist")
-}
-
-func TestFlush(t *testing.T) {
-	// Test error exceptions
-	file := NewFile()
-	streamWriter, err := file.NewStreamWriter("Sheet1")
-	assert.NoError(t, err)
-	streamWriter.Sheet = "SheetN"
-	assert.EqualError(t, streamWriter.Flush(), "sheet SheetN is not exist")
-
 	// Test close temporary file error
 	file = NewFile()
 	streamWriter, err = file.NewStreamWriter("Sheet1")
@@ -64,17 +72,49 @@ func TestFlush(t *testing.T) {
 			row[colID] = rand.Intn(640000)
 		}
 		cell, _ := CoordinatesToCellName(1, rowID)
-		assert.NoError(t, streamWriter.SetRow(cell, &row))
+		assert.NoError(t, streamWriter.SetRow(cell, row))
 	}
-	assert.NoError(t, streamWriter.tmpFile.Close())
+	assert.NoError(t, streamWriter.rawData.Close())
 	assert.Error(t, streamWriter.Flush())
 }
 
+func TestStreamTable(t *testing.T) {
+	file := NewFile()
+	streamWriter, err := file.NewStreamWriter("Sheet1")
+	assert.NoError(t, err)
+
+	// Write some rows. We want enough rows to force a temp file (>16MB).
+	assert.NoError(t, streamWriter.SetRow("A1", []interface{}{"A", "B", "C"}))
+	row := []interface{}{1, 2, 3}
+	for r := 2; r < 10000; r++ {
+		assert.NoError(t, streamWriter.SetRow(fmt.Sprintf("A%d", r), row))
+	}
+
+	// Write a table.
+	assert.NoError(t, streamWriter.AddTable("A1", "C2", ``))
+	assert.NoError(t, streamWriter.Flush())
+
+	// Verify the table has names.
+	var table xlsxTable
+	assert.NoError(t, xml.Unmarshal(file.XLSX["xl/tables/table1.xml"], &table))
+	assert.Equal(t, "A", table.TableColumns.TableColumn[0].Name)
+	assert.Equal(t, "B", table.TableColumns.TableColumn[1].Name)
+	assert.Equal(t, "C", table.TableColumns.TableColumn[2].Name)
+}
+
+func TestNewStreamWriter(t *testing.T) {
+	// Test error exceptions
+	file := NewFile()
+	_, err := file.NewStreamWriter("Sheet1")
+	assert.NoError(t, err)
+	_, err = file.NewStreamWriter("SheetN")
+	assert.EqualError(t, err, "sheet SheetN is not exist")
+}
+
 func TestSetRow(t *testing.T) {
 	// Test error exceptions
 	file := NewFile()
 	streamWriter, err := file.NewStreamWriter("Sheet1")
 	assert.NoError(t, err)
-	assert.EqualError(t, streamWriter.SetRow("A", &[]interface{}{}), `cannot convert cell "A" to coordinates: invalid cell name "A"`)
-	assert.EqualError(t, streamWriter.SetRow("A1", []interface{}{}), `pointer to slice expected`)
+	assert.EqualError(t, streamWriter.SetRow("A", []interface{}{}), `cannot convert cell "A" to coordinates: invalid cell name "A"`)
 }