3

在我们的C#应用程序中，有时应用程序需要打开一个 svg 文件。为此，使用以下代码：

XmlReaderSettings settings = new XmlReaderSettings();
settings.ProhibitDtd = false;
settings.ValidationType = ValidationType.None;
XmlReader xr = XmlReader.Create(serverMainPath + @"/path/to/svg/file.svg", settings);
XmlDocument xd = new XmlDocument();
_nmsm = new XmlNamespaceManager(xd.NameTable);
_nmsm.AddNamespace("svg", "http://www.w3.org/2000/svg");
_nmsm.AddNamespace("v", "http://schemas.microsoft.com/visio/2003/SVGExtensions/");
xd.Load(xr);

我们使用的标准 svg 以（据我所知它是一个有效的 svg）开头：

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
    <!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.0//EN" "http://www.w3.org/TR/2001/REC-SVG-20010904/DTD/svg10.dtd">
    <!-- Généré par Microsoft Visio 11.0, SVG Export, v1.0 svgIncluded.svg Page-1 -->
    <svg xmlns="http://www.w3.org/2000/svg" xmlns:v="http://schemas.microsoft.com/visio/2003/SVGExtensions/" width="8.26772in" height="11.6929in" viewBox="0 0 595.276 841.889" xml:space="preserve" color-interpolation-filters="sRGB" class="st23" >

在过去的 6 个月里，它工作得很好。但是从一两周开始，这段代码有时会产生以下错误：

Server Error in '/ourApp' Application.
--------------------------------------------------------------------------------

The remote server returned an error: (403) Forbidden. 
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.Net.WebException: The remote server returned an error: (403) Forbidden.

Source Error: 

Line 40:                 _nmsm.AddNamespace("svg", "http://www.w3.org/2000/svg");
Line 41:                 _nmsm.AddNamespace("v", "http://schemas.microsoft.com/visio/2003/SVGExtensions/");
Line 42:                 xd.Load(xr);


Source File: path/to/the/file/file.cs    Line: 42 

Stack Trace: 

[WebException: The remote server returned an error: (403) Forbidden.]
   System.Net.HttpWebRequest.GetResponse() +5400333
   System.Xml.XmlDownloadManager.GetNonFileStream(Uri uri, ICredentials credentials) +69
   System.Xml.XmlDownloadManager.GetStream(Uri uri, ICredentials credentials) +3929515
   System.Xml.XmlUrlResolver.GetEntity(Uri absoluteUri, String role, Type ofObjectToReturn) +54
   System.Xml.XmlTextReaderImpl.OpenStream(Uri uri) +34
   System.Xml.XmlTextReaderImpl.DtdParserProxy_PushExternalSubset(String systemId, String publicId) +380

[XmlException: An error has occurred while opening external DTD 'http://www.w3.org/TR/2001/REC-SVG-20010904/DTD/svg10.dtd': The remote server returned an error: (403) Forbidden.]
   System.Xml.XmlTextReaderImpl.Throw(Exception e) +76
   System.Xml.XmlTextReaderImpl.DtdParserProxy_PushExternalSubset(String systemId, String publicId) +513
   System.Xml.DtdParserProxy.System.Xml.IDtdParserAdapter.PushExternalSubset(String systemId, String publicId) +16
   System.Xml.DtdParser.ParseExternalSubset() +21
   System.Xml.DtdParser.ParseInDocumentDtd(Boolean saveInternalSubset) +4017069
   System.Xml.DtdParser.Parse(Boolean saveInternalSubset) +54
   System.Xml.DtdParserProxy.Parse(Boolean saveInternalSubset) +31
   System.Xml.XmlTextReaderImpl.ParseDoctypeDecl() +254
   System.Xml.XmlTextReaderImpl.ParseDocumentContent() +451
   System.Xml.XmlTextReaderImpl.Read() +151
   System.Xml.XmlLoader.LoadNode(Boolean skipOverWhitespace) +58
   System.Xml.XmlLoader.LoadDocSequence(XmlDocument parentDoc) +20
   System.Xml.XmlLoader.Load(XmlDocument doc, XmlReader reader, Boolean preserveWhitespace) +129
   System.Xml.XmlDocument.Load(XmlReader reader) +108
   OurMethod(params) in path/to/the/file/file.cs:42
   StackTrace in our App.

--------------------------------------------------------------------------------
Version Information: Microsoft .NET Framework Version:2.0.50727.3643; ASP.NET Version:2.0.50727.3634

起初我认为这是由于我们的 Internet 代理政策发生了变化，但由于在另一个代理后面的应用程序的另一个部署中发现了它，我非常怀疑这一点。

错误似乎或多或少是随机的，有时它会起作用，有时它不会。我只是不知道它为什么会这样。

问题是：你知道为什么会发生这种情况吗？如果是，您知道如何解决吗？如果没有，任何解决方法的想法？

4

2 回答 2

1

最后，我使用了自制班来完成这项工作。它的灵感来自于XmlUrlResolver 扩展的 MSDN 实现。感谢@mzjn 指出指向 MSDN 资源的链接。

using System;
using System.Net;
using System.Net.Cache;
using System.Xml;
using System.IO;

namespace My.Nasmespace.Class.IO
{
    class XmlExtendedResolver : XmlUrlResolver
    {
        bool enableHttpCaching;
        ICredentials credentials;
        private string localServerPath;
        //resolve ressource from localServerPath if it's possible
        //resolve resources from cache (if possible) when enableHttpCaching is set to true 
        //resolve resources from source when enableHttpcaching is set to false  
        public XmlExtendedResolver(bool enableHttpCaching, string serverPath)
        {
            this.enableHttpCaching = enableHttpCaching;
            localServerPath = serverPath;
        }

        public override ICredentials Credentials
        {
            set
            {
                credentials = value;
                base.Credentials = value;
            }
        }

        public override object GetEntity(Uri absoluteUri, string role, Type ofObjectToReturn)
        {
            if (absoluteUri == null)
            {
                throw new ArgumentNullException("absoluteUri");
            }
            //resolve resources from cache (if possible) 
            if (absoluteUri.Scheme == "http" && enableHttpCaching && (ofObjectToReturn == null || ofObjectToReturn == typeof(Stream)))
            {
                /*Try to resolve it from the local path if it exists*/
                if (!string.IsNullOrEmpty(localServerPath) && absoluteUri.AbsolutePath.EndsWith(".dtd") && !absoluteUri.AbsoluteUri.StartsWith(localServerPath))
                {
                    try { 
                        return GetEntity(new Uri(localServerPath + "/Xml/" + absoluteUri.Segments[absoluteUri.Segments.Length-1]), role, ofObjectToReturn);
                    } catch (FileNotFoundException){
                         //Fail silently to go to the web request.
                    }
                }
                WebRequest webReq = WebRequest.Create(absoluteUri);
                webReq.CachePolicy = new    HttpRequestCachePolicy(HttpRequestCacheLevel.Default);
                if (credentials != null)
                {
                    webReq.Credentials = credentials;
                }
                WebResponse resp = webReq.GetResponse();
                return resp.GetResponseStream();
            }
            //otherwise use the default behavior of the XmlUrlResolver class (resolve resources from source) 
        else
            {
                return base.GetEntity(absoluteUri, role, ofObjectToReturn);
            }
        }
    }
}
于 2013-03-13T07:34:32.757 回答
0

我认为你必须围绕这个尝试一些逻辑，我只是​​从某个地方缓冲

request.UserAgent = "userAgents";
request.Accept = "*/*";

和

request.Credentials = new NetworkCredentials("username", "password");

or 

 request.Credentials = CredentialCache.DefaultCredentials;
于 2013-03-18T07:23:52.023 回答