开箱即用XMLWorker 只能理解绝对 URI，因此所描述的问题是预期的行为。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。
实施ILinkProvider修复了损坏的超链接问题，实施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。下面的帮助类做到了这一点，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");
}
}
现在实现ILinkProvider非常简单，它UriHelper给出了基本的 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只需要实现一个方法，Retrieve(string src)但是Store(string src, Image img)很容易 - 注意那里和 for 的内联注释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() { }
}
根据XML Worker 文档ILinkProvider，将以上的实现挂钩IImageProvider到一个简单的解析器类非常简单：
/* 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);
}
}
}
}
如内联注释，SimpleAjaxImgFix(string xHtml)专门处理可能发送未关闭标签的XHR<img>，这是有效 HTML的，但无效 XML的会中断XMLWorker。可以在此处找到有关如何使用 XHR 和 iTextSharp 接收 PDF 或其他二进制数据的简单说明和实现。
使用ARegex是为了SimpleAjaxImgFix(string xHtml)让任何使用（复制/粘贴？）代码的人都不需要添加另一个nuget包，但应该使用像HtmlAgilityPackHTML这样的解析器 ，因为轮到了：
<div><img src='a.gif'><br><hr></div>
进入这个：
<div><img src='a.gif' /><br /><hr /></div>
只有几行代码：
var hDocument = new HtmlDocument()
{
OptionWriteEmptyNodes = true,
OptionAutoCloseOnEnd = true
};
hDocument.LoadHtml("<div><img src='a.gif'><br><hr></div>");
var closedTags = hDocument.DocumentNode.WriteTo();
还需要注意的是，将SimpleParser.Parse()上述用作额外实现自定义ICSSResolver或ITagProcessorFactory的通用蓝图，文档中对此进行了说明。
现在应该注意问题中描述的问题。从调用MVC Action Method：
[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();
}
或从服务器控件Web Form获取的：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 <img>: <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);
}
答案很长，但请查看此处标记为 、 和 的问题html，pdf截至itextsharp撰写本文时（2016 年 2 月 23 日），共有776 个结果，而标记itextsharp的总数为 4,063 - 即19%。