feat(文档导出): 优化大文档流式导出，降低内存占用

assets/webui/ofdgo.js

@@ -1496,26 +1496,41 @@ async function exportFile(whole) {
 		return;
 	}
 	const label = whole ? (format.value === "pdf" ? "PDF" : "ZIP") : format.label;
+	const extension = whole ? label.toLowerCase() : format.extension;
+	const mime = whole && format.value !== "pdf" ? "application/zip" : format.mime;
 	const openSeq = state.openSeq;
-	const fileName = whole ? `${baseFileName()}.${label.toLowerCase()}` : pageFileName(format.extension);
+	const fileName = whole ? `${baseFileName()}.${extension}` : pageFileName(extension);
+	const pageIndex = state.pageIndex;
+	const dpi = exportFormatUsesDPI(format.value) ? currentImageDPI() : 0;
 	state.exporting = true;
 	updateControls();
 	setBusy(true, `正在生成 ${label}`, null, whole ? STATUS.exporting : STATUS.pageExporting);
 	try {
-		const dpi = exportFormatUsesDPI(format.value) ? currentImageDPI() : 0;
+		const file = window.showSaveFilePicker ? await window.showSaveFilePicker({
+			suggestedName: fileName,
+			types: [{ description: label, accept: { [mime]: [`.${extension}`] } }],
+		}) : null;
+		if (openSeq !== state.openSeq) {
+			return;
+		}
 		const result = whole
-			? await callWASM("ofdgoExportDocument", format.value, dpi)
-			: await callWASM("ofdgoExportPage", state.pageIndex, format.value, dpi);
+			? await callWASM("ofdgoExportDocument", format.value, dpi, file)
+			: await callWASM("ofdgoExportPage", pageIndex, format.value, dpi, file);
 		if (openSeq !== state.openSeq) {
 			return;
 		}
 		setProgress(`正在保存 ${result.label}`, 100);
-		const bytes = result.bytes;
-		downloadBytes(bytes, result.mime, fileName);
-		setStatus(`${result.label} 导出完成 ${formatBytes(bytes.length, result.label)}`);
+		if (result.blob) {
+			downloadBytes(result.blob, result.mime, fileName);
+		}
+		setStatus(`${result.label} 导出完成 ${formatBytes(result.size, result.label)}`);
 	} catch (err) {
 		if (openSeq === state.openSeq) {
-			showError(err, false);
+			if (err.name === "AbortError") {
+				setStatus("导出已取消");
+			} else {
+				showError(err, false);
+			}
 		}
 	} finally {
 		state.exporting = false;

assets/webui/ofdgo.wasm.js

@@ -1,14 +1,49 @@
 importScripts("./wasm_exec.js");
 
-self.onmessage = ({ data: { id, name, args } }) => {
+let pending = Promise.resolve();
+self.onmessage = ({ data }) => {
+	pending = pending.then(() => handleMessage(data));
+};
+async function handleMessage({ id, name, args }) {
+	let output;
 	try {
-		const payload = globalThis[name](...args);
+		const chunks = [];
+		let size = 0;
+		const exporting = name === "ofdgoExportPage" || name === "ofdgoExportDocument";
+		if (exporting) {
+			const file = args.pop();
+			if (file) {
+				output = await file.createWritable();
+			}
+			args.push((bytes, done) => {
+				size += bytes.length;
+				if (output) {
+					output.write(bytes).then(() => done(), (err) => done(err.message));
+				} else {
+					chunks.push(new Blob([bytes]));
+					setTimeout(done, 0);
+				}
+			});
+		}
+		const payload = await globalThis[name](...args);
 		const result = typeof payload === "string" ? JSON.parse(payload) : payload;
+		if (exporting && result.ok) {
+			result.data.size = size;
+			if (output) {
+				await output.close();
+			} else {
+				result.data.blob = new Blob(chunks, { type: result.data.mime });
+			}
+		} else if (output) {
+			await output.abort();
+		}
+		output = null;
 		self.postMessage({ id, ...result }, result.data?.bytes ? [result.data.bytes.buffer] : []);
 	} catch (err) {
+		await output?.abort().catch(() => {});
 		self.postMessage({ id, ok: false, error: err.message });
 	}
-};
+}
 
 function exitWASM(err) {
 	self.postMessage({ type: "exit", error: err?.message || "引擎运行中断" });

internal/webui/wasm.go

@@ -17,11 +17,43 @@
 package webui
 
 import (
+	"bufio"
 	"encoding/json"
 	"fmt"
 	"syscall/js"
 )
 
+// exportWriter 分块传递导出数据
+type exportWriter struct {
+	write js.Value
+}
+
+// Write 将数据块交给浏览器保存
+// 入参: data 导出数据
+// 返回: int 写入长度, error 错误信息
+func (w exportWriter) Write(data []byte) (int, error) {
+	done := make(chan error)
+	callback := js.FuncOf(func(this js.Value, args []js.Value) any {
+		var err error
+		if len(args) > 0 {
+			err = fmt.Errorf("%s", args[0].String())
+		}
+		done <- err
+		return nil
+	})
+	defer callback.Release()
+	size := len(data)
+	for len(data) > 0 {
+		n := min(len(data), 1<<20)
+		w.write.Invoke(bytesToJS(data[:n]), callback)
+		if err := <-done; err != nil {
+			return size - len(data), err
+		}
+		data = data[n:]
+	}
+	return size, nil
+}
+
 // currentSession 当前WebUI文档会话
 var currentSession *Session
 
@@ -42,8 +74,8 @@ func RunWASM() {
 	registerCallback("ofdgoSVGFontData", svgFontData)
 	registerCallback("ofdgoSearchPage", searchPage)
 	registerCallback("ofdgoExportFormats", exportFormats)
-	registerCallback("ofdgoExportPage", exportPage)
-	registerCallback("ofdgoExportDocument", exportDocument)
+	registerExportCallback("ofdgoExportPage", exportPage)
+	registerExportCallback("ofdgoExportDocument", exportDocument)
 	registerCallback("ofdgoMatchFontFiles", matchFontFiles)
 	select {}
 }
@@ -52,18 +84,42 @@ func RunWASM() {
 // 入参: name 回调名称, fn 回调函数
 func registerCallback(name string, fn func([]js.Value) (any, error)) {
 	cb := js.FuncOf(func(this js.Value, args []js.Value) any {
-		data, err := safeCall(fn, args)
-		if err != nil {
-			return encodeResult(apiResult{OK: false, Error: err.Error()})
-		}
-		if result, ok := data.(js.Value); ok {
-			return result
-		}
-		return encodeResult(apiResult{OK: true, Data: data})
+		return callbackResult(fn, args)
 	})
 	js.Global().Set(name, cb)
 }
 
+// registerExportCallback 异步导出，为浏览器处理数据块让出事件循环
+// 入参: name 回调名称, fn 回调函数
+func registerExportCallback(name string, fn func([]js.Value) (any, error)) {
+	cb := js.FuncOf(func(this js.Value, args []js.Value) any {
+		executor := js.FuncOf(func(this js.Value, callbacks []js.Value) any {
+			resolve := callbacks[0]
+			go func() {
+				resolve.Invoke(callbackResult(fn, args))
+			}()
+			return nil
+		})
+		defer executor.Release()
+		return js.Global().Get("Promise").New(executor)
+	})
+	js.Global().Set(name, cb)
+}
+
+// callbackResult 转换浏览器接口结果
+// 入参: fn 回调函数, args 回调参数
+// 返回: any 浏览器结果
+func callbackResult(fn func([]js.Value) (any, error), args []js.Value) any {
+	data, err := safeCall(fn, args)
+	if err != nil {
+		return encodeResult(apiResult{OK: false, Error: err.Error()})
+	}
+	if result, ok := data.(js.Value); ok {
+		return result
+	}
+	return encodeResult(apiResult{OK: true, Data: data})
+}
+
 // safeCall 调用浏览器回调并转换异常
 // 入参: fn 回调函数, args 回调参数
 // 返回: any 回调结果, error 错误信息
@@ -238,15 +294,18 @@ func exportPage(args []js.Value) (any, error) {
 	if currentSession == nil {
 		return nil, fmt.Errorf("ofd document is not opened")
 	}
-	if len(args) < 3 {
+	if len(args) < 4 {
 		return nil, fmt.Errorf("missing export page arguments")
 	}
-	data, format, err := currentSession.ExportPage(args[0].Int(), args[1].String(), args[2].Float())
+	writer := bufio.NewWriterSize(exportWriter{write: args[3]}, 1<<20)
+	format, err := currentSession.ExportPage(args[0].Int(), args[1].String(), args[2].Float(), writer)
 	if err != nil {
 		return nil, err
 	}
+	if err := writer.Flush(); err != nil {
+		return nil, err
+	}
 	return successResult(map[string]any{
-		"bytes": bytesToJS(data),
 		"label": format.Label,
 		"mime":  format.MIME,
 	}), nil
@@ -259,12 +318,15 @@ func exportDocument(args []js.Value) (any, error) {
 	if currentSession == nil {
 		return nil, fmt.Errorf("ofd document is not opened")
 	}
-	data, format, err := currentSession.ExportDocument(args[0].String(), args[1].Float())
+	writer := bufio.NewWriterSize(exportWriter{write: args[2]}, 1<<20)
+	format, err := currentSession.ExportDocument(args[0].String(), args[1].Float(), writer)
 	if err != nil {
 		return nil, err
 	}
+	if err := writer.Flush(); err != nil {
+		return nil, err
+	}
 	return successResult(map[string]any{
-		"bytes": bytesToJS(data),
 		"label": format.Label,
 		"mime":  format.MIME,
 	}), nil

internal/webui/webui.go

@@ -15,12 +15,10 @@
 package webui
 
 import (
-	"archive/zip"
 	"bytes"
 	"fmt"
-	"image/jpeg"
+	"io"
 	"path"
-	"strconv"
 	"strings"
 	"time"
 
@@ -450,38 +448,22 @@ func (s *Session) SVGFontData(name string) ([]byte, error) {
 }
 
 // ExportPage 导出单页
-// 入参: index 页面索引, value 导出格式, dpi 图片DPI
-// 返回: []byte 文件数据, ExportFormat 导出格式, error 错误信息
-func (s *Session) ExportPage(index int, value string, dpi float64) ([]byte, ExportFormat, error) {
+// 入参: index 页面索引, value 导出格式, dpi 图片DPI, writer 输出流
+// 返回: ExportFormat 导出格式, error 错误信息
+func (s *Session) ExportPage(index int, value string, dpi float64, writer io.Writer) (ExportFormat, error) {
 	format, ok := exportFormat(value)
 	if !ok {
-		return nil, ExportFormat{}, fmt.Errorf("unsupported export format %s", value)
+		return ExportFormat{}, fmt.Errorf("unsupported export format %s", value)
 	}
 	page, err := s.pageContent(index)
 	if err != nil {
-		return nil, ExportFormat{}, err
+		return ExportFormat{}, err
 	}
-	var buf bytes.Buffer
 	renderer := *s.Renderer
 	if dpi > 0 && (format.Value == "png" || format.Value == "jpg") {
 		renderer.DPI = dpi
 	}
-	switch format.Value {
-	case "svg":
-		err = renderer.RenderToSVG(page, &buf)
-	case "pdf":
-		err = renderer.RenderToPDF(page, &buf)
-	case "eps":
-		err = renderer.RenderToEPS(page, &buf)
-	case "png":
-		err = renderer.RenderToPNG(page, &buf)
-	case "jpg":
-		err = renderer.RenderToJPEG(page, &buf, &jpeg.Options{Quality: 95})
-	}
-	if err != nil {
-		return nil, ExportFormat{}, err
-	}
-	return buf.Bytes(), format, nil
+	return format, renderer.RenderTo(page, writer, format.Value)
 }
 
 // signatureInfos 获取签名验证信息
@@ -632,72 +614,43 @@ func signatureStampInfos(positions []ofdgo.SignatureStampPosition) []SignatureSt
 }
 
 // ExportDocument 导出文档为PDF或逐页打包ZIP
-// 入参: value 导出格式, dpi 图片DPI
-// 返回: []byte 文件数据, ExportFormat 导出格式, error 错误信息
-func (s *Session) ExportDocument(value string, dpi float64) ([]byte, ExportFormat, error) {
+// 入参: value 导出格式, dpi 图片DPI, writer 输出流
+// 返回: ExportFormat 导出格式, error 错误信息
+func (s *Session) ExportDocument(value string, dpi float64, writer io.Writer) (ExportFormat, error) {
 	format, ok := exportFormat(value)
 	if !ok {
-		return nil, ExportFormat{}, fmt.Errorf("unsupported export format %s", value)
+		return ExportFormat{}, fmt.Errorf("unsupported export format %s", value)
 	}
 	if format.Value == "pdf" {
-		data, err := s.ExportPDF()
-		return data, format, err
+		return format, s.ExportPDF(writer)
 	}
 	if s == nil || s.Reader == nil || s.Renderer == nil || s.doc == nil {
-		return nil, ExportFormat{}, fmt.Errorf("ofd document is not opened")
+		return ExportFormat{}, fmt.Errorf("ofd document is not opened")
 	}
-	count := len(s.doc.Pages.Page)
-	if count == 0 {
-		return nil, ExportFormat{}, fmt.Errorf("no pages found")
+	renderer := *s.Renderer
+	if dpi > 0 && (format.Value == "png" || format.Value == "jpg") {
+		renderer.DPI = dpi
 	}
-	var buf bytes.Buffer
-	archive := zip.NewWriter(&buf)
-	method := zip.Deflate
-	if format.Value == "png" || format.Value == "jpg" {
-		method = zip.Store
-	}
-	width := len(strconv.Itoa(count))
-	for index := range count {
-		data, _, err := s.ExportPage(index, format.Value, dpi)
-		if err != nil {
-			return nil, ExportFormat{}, fmt.Errorf("failed to export page %d: %w", index+1, err)
-		}
-		entry, err := archive.CreateHeader(&zip.FileHeader{
-			Name:   fmt.Sprintf("%0*d.%s", width, index+1, format.Extension),
-			Method: method,
-		})
-		if err != nil {
-			return nil, ExportFormat{}, err
-		}
-		if _, err := entry.Write(data); err != nil {
-			return nil, ExportFormat{}, err
-		}
-	}
-	if err := archive.Close(); err != nil {
-		return nil, ExportFormat{}, err
-	}
-	return buf.Bytes(), ExportFormat{Value: "zip", Label: "ZIP", Extension: "zip", MIME: "application/zip"}, nil
+	err := renderer.RenderToZIP(writer, format.Value)
+	return ExportFormat{Value: "zip", Label: "ZIP", Extension: "zip", MIME: "application/zip"}, err
 }
 
 // ExportPDF 导出文档为PDF
-// 返回: []byte PDF文件数据, error 错误信息
-func (s *Session) ExportPDF() ([]byte, error) {
+// 入参: writer 输出流
+// 返回: error 错误信息
+func (s *Session) ExportPDF(writer io.Writer) error {
 	if s == nil || s.Reader == nil || s.Renderer == nil || s.doc == nil {
-		return nil, fmt.Errorf("ofd document is not opened")
+		return fmt.Errorf("ofd document is not opened")
 	}
-	var buf bytes.Buffer
 	pages := make([]*ofdgo.PageContent, len(s.doc.Pages.Page))
 	for i := range pages {
 		page, err := s.pageContent(i)
 		if err != nil {
-			return nil, err
+			return err
 		}
 		pages[i] = page
 	}
-	if err := s.Renderer.RenderPagesToPDF(pages, &buf); err != nil {
-		return nil, err
-	}
-	return buf.Bytes(), nil
+	return s.Renderer.RenderPagesToPDF(pages, writer)
 }
 
 // pageContent 获取页面内容

ofdgo_renderer_output.go

@@ -15,6 +15,7 @@
 package ofdgo
 
 import (
+	"archive/zip"
 	"bufio"
 	"bytes"
 	"fmt"
@@ -22,6 +23,8 @@ import (
 	"image/jpeg"
 	"image/png"
 	"io"
+	"strconv"
+	"strings"
 
 	"github.com/tdewolff/canvas"
 	"github.com/tdewolff/canvas/renderers/pdf"
@@ -32,6 +35,79 @@ import (
 	"golang.org/x/image/math/f64"
 )
 
+// RenderTo 按格式渲染单页，JPEG使用95画质
+// 入参: page 页面内容, writer 输出流, format svg、pdf、eps、png、jpg或jpeg
+// 返回: error 错误信息
+func (r *Renderer) RenderTo(page *PageContent, writer io.Writer, format string) error {
+	_, render, err := r.outputRenderer(format)
+	if err != nil {
+		return err
+	}
+	return render(page, writer)
+}
+
+// outputRenderer 获取格式扩展名和渲染方法
+// 入参: format 输出格式
+// 返回: string 扩展名, func 渲染方法, error 错误信息
+func (r *Renderer) outputRenderer(format string) (string, func(*PageContent, io.Writer) error, error) {
+	switch strings.ToLower(strings.TrimSpace(format)) {
+	case "svg":
+		return "svg", r.RenderToSVG, nil
+	case "pdf":
+		return "pdf", r.RenderToPDF, nil
+	case "eps":
+		return "eps", r.RenderToEPS, nil
+	case "png":
+		return "png", r.RenderToPNG, nil
+	case "jpg", "jpeg":
+		return "jpg", func(page *PageContent, writer io.Writer) error {
+			return r.RenderToJPEG(page, writer, &jpeg.Options{Quality: 95})
+		}, nil
+	default:
+		return "", nil, fmt.Errorf("unsupported output format %s", format)
+	}
+}
+
+// RenderToZIP 逐页渲染并写入ZIP，文件编号按总页数补零，出错时调用方应丢弃输出
+// 入参: writer 输出流, format svg、pdf、eps、png、jpg或jpeg
+// 返回: error 错误信息
+func (r *Renderer) RenderToZIP(writer io.Writer, format string) error {
+	extension, render, err := r.outputRenderer(format)
+	if err != nil {
+		return err
+	}
+	count, err := r.Reader.PageCount()
+	if err != nil {
+		return err
+	}
+	if count == 0 {
+		return fmt.Errorf("no pages found")
+	}
+	archive := zip.NewWriter(writer)
+	method := zip.Deflate
+	if extension == "png" || extension == "jpg" {
+		method = zip.Store
+	}
+	width := len(strconv.Itoa(count))
+	for index := range count {
+		page, err := r.Reader.PageContentByIndex(index)
+		if err != nil {
+			return fmt.Errorf("failed to read page %d: %w", index+1, err)
+		}
+		entry, err := archive.CreateHeader(&zip.FileHeader{
+			Name:   fmt.Sprintf("%0*d.%s", width, index+1, extension),
+			Method: method,
+		})
+		if err != nil {
+			return err
+		}
+		if err := render(page, entry); err != nil {
+			return fmt.Errorf("failed to export page %d: %w", index+1, err)
+		}
+	}
+	return archive.Close()
+}
+
 // rasterRenderer 保留页面物理尺寸的光栅渲染器
 type rasterRenderer struct {
 	*rasterizer.Rasterizer
@@ -139,9 +215,13 @@ func (r *Renderer) RenderToSVG(page *PageContent, writer io.Writer) error {
 	if err != nil {
 		return err
 	}
-	renderer := svg.New(writer, c.W, c.H, nil)
+	buffer := bufio.NewWriter(writer)
+	renderer := svg.New(buffer, c.W, c.H, nil)
 	c.RenderTo(renderer)
-	return renderer.Close()
+	if err := renderer.Close(); err != nil {
+		return err
+	}
+	return buffer.Flush()
 }
 
 // replacePDFProducer 替换PDF的Producer属性