如何使用 iText 将带有图像和超链接的 HTML 转换为 PDF？

问题描述 投票：0回答：2

我正在尝试在同时使用 

MVC
、
和 
web 表单
的
pdf itext html-parsing html-agility-pack xmlworker
2个回答
12
投票
XMLWorker

仅理解绝对URI，因此所描述的问题是预期行为。如果没有一些附加信息，解析器无法自动推断出 URI 方案 或路径。 

实现 
ILinkProvider
 修复了损坏的超链接问题，并实现 IImageProvider 修复了损坏的图像问题。由于两种实现都必须执行 URI 解析，这是第一步。下面的帮助器类就做到了这一点，并且还尝试使 Web (ASP.NET) 上下文调用（示例如下）尽可能简单：


// resolve URIs for LinkProvider & ImageProvider
public class UriHelper
{
    /* IsLocal; when running in web context:
     * [1] give LinkProvider http[s] scheme; see CreateBase(string baseUri)
     * [2] give ImageProvider relative path starting with '/' - see:
     *     Join(string relativeUri)
     */
    public bool IsLocal { get; set; }
    public HttpContext HttpContext { get; private set; }
    public Uri BaseUri { get; private set; }

    public UriHelper(string baseUri) : this(baseUri, true) {}
    public UriHelper(string baseUri, bool isLocal)
    {
        IsLocal = isLocal;
        HttpContext = HttpContext.Current;
        BaseUri = CreateBase(baseUri);
    }

    /* get URI for IImageProvider to instantiate iTextSharp.text.Image for 
     * each <img> element in the HTML.
     */
    public string Combine(string relativeUri)
    {
        /* when running in a web context, the HTML is coming from a MVC view 
         * or web form, so convert the incoming URI to a **local** path
         */
        if (HttpContext != null && !BaseUri.IsAbsoluteUri && IsLocal)
        {
            return HttpContext.Server.MapPath(
                // Combine() checks directory traversal exploits
                VirtualPathUtility.Combine(BaseUri.ToString(), relativeUri)
            );
        }
        return BaseUri.Scheme == Uri.UriSchemeFile 
            ? Path.Combine(BaseUri.LocalPath, relativeUri)
            // for this example we're assuming URI.Scheme is http[s]
            : new Uri(BaseUri, relativeUri).AbsoluteUri;
    }

    private Uri CreateBase(string baseUri)
    {
        if (HttpContext != null)
        {   // running on a web server; need to update original value  
            var req = HttpContext.Request;
            baseUri = IsLocal
                // IImageProvider; absolute virtual path (starts with '/')
                // used to convert to local file system path. see:
                // Combine(string relativeUri)
                ? req.ApplicationPath
                // ILinkProvider; absolute http[s] URI scheme
                : req.Url.GetLeftPart(UriPartial.Authority)
                    + HttpContext.Request.ApplicationPath;
        }

        Uri uri;
        if (Uri.TryCreate(baseUri, UriKind.RelativeOrAbsolute, out uri)) return uri;

        throw new InvalidOperationException("cannot create a valid BaseUri");
    }
}




实现 
ILinkProvider
 非常简单，因为 
UriHelper
 给出了基本 URI。我们只需要正确的 URI 方案（
file
 或 
http[s]
）：


// make hyperlinks with relative URLs absolute
public class LinkProvider : ILinkProvider
{
    // rfc1738 - file URI scheme section 3.10
    public const char SEPARATOR = '/';
    public string BaseUrl { get; private set; }

    public LinkProvider(UriHelper uriHelper)
    {
        var uri = uriHelper.BaseUri;
        /* simplified implementation that only takes into account:
         * Uri.UriSchemeFile || Uri.UriSchemeHttp || Uri.UriSchemeHttps
         */
        BaseUrl = uri.Scheme == Uri.UriSchemeFile
            // need trailing separator or file paths break
            ? uri.AbsoluteUri.TrimEnd(SEPARATOR) + SEPARATOR
            // assumes Uri.UriSchemeHttp || Uri.UriSchemeHttps
            : BaseUrl = uri.AbsoluteUri;
    }

    public string GetLinkRoot()
    {
        return BaseUrl;
    }
}




IImageProvider
仅
需要
实现单个方法，Retrieve(string src)，但是
Store(string src, Image img)
很简单 - 请注意那里的内联注释和
GetImageRootPath()
：


// handle <img> elements in HTML  
public class ImageProvider : IImageProvider
{
    private UriHelper _uriHelper;
    // see Store(string src, Image img)
    private Dictionary<string, Image> _imageCache = 
        new Dictionary<string, Image>();

    public virtual float ScalePercent { get; set; }
    public virtual Regex Base64 { get; set; }

    public ImageProvider(UriHelper uriHelper) : this(uriHelper, 67f) { }
    //              hard-coded based on general past experience ^^^
    // but call the overload to supply your own
    public ImageProvider(UriHelper uriHelper, float scalePercent)
    {
        _uriHelper = uriHelper;
        ScalePercent = scalePercent;
        Base64 = new Regex( // rfc2045, section 6.8 (alphabet/padding)
            @"^data:image/[^;]+;base64,(?<data>[a-z0-9+/]+={0,2})$",
            RegexOptions.Compiled | RegexOptions.IgnoreCase
        );
    }

    public virtual Image ScaleImage(Image img)
    {
        img.ScalePercent(ScalePercent);
        return img;
    }

    public virtual Image Retrieve(string src)
    {
        if (_imageCache.ContainsKey(src)) return _imageCache[src];

        try
        {
            if (Regex.IsMatch(src, "^https?://", RegexOptions.IgnoreCase))
            {
                return ScaleImage(Image.GetInstance(src));
            }

            Match match;
            if ((match = Base64.Match(src)).Length > 0)
            {
                return ScaleImage(Image.GetInstance(
                    Convert.FromBase64String(match.Groups["data"].Value)
                ));
            }

            var imgPath = _uriHelper.Combine(src);
            return ScaleImage(Image.GetInstance(imgPath));
        }
        // not implemented to keep the SO answer (relatively) short
        catch (BadElementException ex) { return null; }
        catch (IOException ex) { return null; }
        catch (Exception ex) { return null; }
    }

    /*
     * always called after Retrieve(string src):
     * [1] cache any duplicate <img> in the HTML source so the image bytes
     *     are only written to the PDF **once**, which reduces the 
     *     resulting file size.
     * [2] the cache can also **potentially** save network IO if you're
     *     running the parser in a loop, since Image.GetInstance() creates
     *     a WebRequest when an image resides on a remote server. couldn't
     *     find a CachePolicy in the source code
     */
    public virtual void Store(string src, Image img)
    {
        if (!_imageCache.ContainsKey(src)) _imageCache.Add(src, img);
    }

    /* XMLWorker documentation for ImageProvider recommends implementing
     * GetImageRootPath():
     * 
     * http://demo.itextsupport.com/xmlworker/itextdoc/flatsite.html#itextdoc-menu-10
     * 
     * but a quick run through the debugger never hits the breakpoint, so 
     * not sure if I'm missing something, or something has changed internally 
     * with XMLWorker....
     */
    public virtual string GetImageRootPath() { return null; }
    public virtual void Reset() { }
}




基于 
XML Worker 文档
，将上面 ILinkProvider 和 
IImageProvider
 的实现挂接到一个简单的解析器类中非常简单：


/* a simple parser that uses XMLWorker and XMLParser to handle converting 
 * (most) images and hyperlinks internally
 */
public class SimpleParser
{
    public virtual ILinkProvider LinkProvider { get; set; }
    public virtual IImageProvider ImageProvider { get; set; }

    public virtual HtmlPipelineContext HtmlPipelineContext { get; set; }
    public virtual ITagProcessorFactory TagProcessorFactory { get; set; }
    public virtual ICSSResolver CssResolver { get; set; }

    /* overloads simplfied to keep SO answer (relatively) short. if needed
     * set LinkProvider/ImageProvider after instantiating SimpleParser()
     * to override the defaults (e.g. ImageProvider.ScalePercent)
     */
    public SimpleParser() : this(null) { }
    public SimpleParser(string baseUri)
    {
        LinkProvider = new LinkProvider(new UriHelper(baseUri, false));
        ImageProvider = new ImageProvider(new UriHelper(baseUri, true));

        HtmlPipelineContext = new HtmlPipelineContext(null);

        // another story altogether, and not implemented for simplicity 
        TagProcessorFactory = Tags.GetHtmlTagProcessorFactory();
        CssResolver = XMLWorkerHelper.GetInstance().GetDefaultCssResolver(true);
    }

    /*
     * when sending XHR via any of the popular JavaScript frameworks,
     * <img> tags are **NOT** always closed, which results in the 
     * infamous iTextSharp.tool.xml.exceptions.RuntimeWorkerException:
     * 'Invalid nested tag a found, expected closing tag img.' a simple
     * workaround.
     */
    public virtual string SimpleAjaxImgFix(string xHtml)
    {
        return Regex.Replace(
            xHtml,
            "(?<image><img[^>]+)(?<=[^/])>",
            new MatchEvaluator(match => match.Groups["image"].Value + " />"),
            RegexOptions.IgnoreCase | RegexOptions.Multiline
        );
    }

    public virtual void Parse(Stream stream, string xHtml)
    {
        xHtml = SimpleAjaxImgFix(xHtml);

        using (var stringReader = new StringReader(xHtml))
        {
            using (Document document = new Document())
            {
                PdfWriter writer = PdfWriter.GetInstance(document, stream);
                document.Open();

                HtmlPipelineContext
                    .SetTagFactory(Tags.GetHtmlTagProcessorFactory())
                    .SetLinkProvider(LinkProvider)
                    .SetImageProvider(ImageProvider)
                ;
                var pdfWriterPipeline = new PdfWriterPipeline(document, writer);
                var htmlPipeline = new HtmlPipeline(HtmlPipelineContext, pdfWriterPipeline);
                var cssResolverPipeline = new CssResolverPipeline(CssResolver, htmlPipeline);

                XMLWorker worker = new XMLWorker(cssResolverPipeline, true);
                XMLParser parser = new XMLParser(worker);
                parser.Parse(stringReader);
            }
        }
    }
}




正如内联注释的那样，
SimpleAjaxImgFix(string xHtml)
专门处理
XHR，
may发送未关闭的<img>标签
，这是
validHTML，但是
invalid
XML，
will
打破XMLWorker。有关如何使用 XHR 和 iTextSharp 接收 PDF 或其他二进制数据的简单说明和实现
可以在此处找到
。 

在 
Regex
 中使用了 
SimpleAjaxImgFix(string xHtml)
，这样任何使用（
复制/粘贴
？）代码的人都不需要添加另一个 nuget 包，而是像 
HtmlAgilityPack
 那样的 
HTML
 解析器应该被使用，因为它变成了这样：

<div><img src='a.gif'><br><hr></div>




进入这个：



<div><img src='a.gif' /><br /><hr /></div>




只需几行代码：



var hDocument = new HtmlDocument()
{
    OptionWriteEmptyNodes = true,
    OptionAutoCloseOnEnd = true
};
hDocument.LoadHtml("<div><img src='a.gif'><br><hr></div>");
var closedTags  = hDocument.DocumentNode.WriteTo();




还值得注意 - 使用上面的 
SimpleParser.Parse()
 作为 
general
 蓝图来额外实现自定义 ICSSResolver 或 ITagProcessorFactory，这在文档中中有解释。

现在应该注意问题中描述的问题。来自 MVC Action Method
 的呼叫：



[HttpPost]  // some browsers have URL length limits
[ValidateInput(false)] // or throws HttpRequestValidationException
public ActionResult Index(string xHtml)
{
    Response.ContentType = "application/pdf";
    Response.AppendHeader(
        "Content-Disposition", "attachment; filename=test.pdf"
    );
    var simpleParser = new SimpleParser();
    simpleParser.Parse(Response.OutputStream, xHtml);

    return new EmptyResult();
}




或从 
Web Form
 从 
服务器控件
获取 
HTML
:


Response.ContentType = "application/pdf";
Response.AppendHeader("Content-Disposition", "attachment; filename=test.pdf");
using (var stringWriter = new StringWriter())
{
    using (var htmlWriter = new HtmlTextWriter(stringWriter))
    {
        ConvertControlToPdf.RenderControl(htmlWriter);
    }
    var simpleParser = new SimpleParser();
    simpleParser.Parse(Response.OutputStream, stringWriter.ToString());
}
Response.End();



 或者文件系统上带有超链接和图像的简单 HTML 文件：


<h1>HTML Page 00 on Local File System</h1>
<div>
    <div>
        Relative &lt;img&gt;: <img src='Images/alt-gravatar.png' />
    </div>
    <div>
        Hyperlink to file system HTML page: 
        <a href='file-system-html-01.html'>Page 01</a>
    </div>
</div>




 或来自远程网站的 HTML：


<div>
    <div>
        <img width="200" alt="Wikipedia Logo"
             src="portal/wikipedia.org/assets/img/Wikipedia-logo-v2.png">
    </div>
    <div lang="en">
        <a href="https://en.wikipedia.org/">English</a>
    </div>
    <div lang="en">
        <a href="wiki/IText">iText</a>
    </div>
</div>




以上两个 
HTML
 片段从控制台应用程序运行：



var filePaths = Path.Combine(basePath, "file-system-html-00.html");
var htmlFile = File.ReadAllText(filePaths);
var remoteUrl = Path.Combine(basePath, "wikipedia.html");
var htmlRemote = File.ReadAllText(remoteUrl);
var outputFile = Path.Combine(basePath, "filePaths.pdf");
var outputRemote = Path.Combine(basePath, "remoteUrl.pdf");

using (var stream = new FileStream(outputFile, FileMode.Create))
{
    var simpleParser = new SimpleParser(basePath);
    simpleParser.Parse(stream, htmlFile);
}
using (var stream = new FileStream(outputRemote, FileMode.Create))
{
    var simpleParser = new SimpleParser("https://wikipedia.org");
    simpleParser.Parse(stream, htmlRemote);
}




相当长的答案，但是看看这里标记为
html
、pdf
和
itextsharp
的问题，截至撰写本文时（2016年2月23日），有
776个结果
与4,063个结果已标记总数 itextsharp
 -那是 
19%。 
    




    

    
    
    

    

        

            

                

                    
0
投票

                    
                

            

        

        


我的问题是将报告 html 中的图像渲染为 pdf。有了你的帖子我就能做到。


我正在使用 ASP.NET MVC 5。


我只需改变
ImageProviderClass
的这个方法：
public virtual string GetImageRootPath() { return null; }



到


public virtual string GetImageRootPath() { HostingEnvironment.MapPath("~/Content/Images/") }



谢谢！

    

	

    

    


  

  

    
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