我为ImageResizer编写了自定义VirtualPathProvider
在public Stream GetStream(long id)方法中，如果找不到文件，我返回Stream.Null。
if (!File.Exists(absoluteFilePath)) return Stream.Null;
但ImageResizer会抛出一个异常，因为以下内容发送给客户：
<!DOCTYPE html>
<html>
<head>
<title>Source stream is empty; it has a length of 0. No bytes, no data. We can't work with this.</title>
<meta name="viewport" content="width=device-width" />
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body {font-family:"Verdana";font-weight:normal;font-size: .7em;color:black;}
p {font-family:"Verdana";font-weight:normal;color:black;margin-top: -5px}
b {font-family:"Verdana";font-weight:bold;color:black;margin-top: -5px}
H1 { font-family:"Verdana";font-weight:normal;font-size:18pt;color:red }
H2 { font-family:"Verdana";font-weight:normal;font-size:14pt;color:maroon }
pre {font-family:"Consolas","Lucida Console",Monospace;font-size:11pt;margin:0;padding:0.5em;line-height:14pt}
.marker {font-weight: bold; color: black;text-decoration: none;}
.version {color: gray;}
.error {margin-bottom: 10px;}
.expandable { text-decoration:underline; font-weight:bold; color:navy; cursor:hand; }
@media screen and (max-width: 639px) {
pre { width: 440px; overflow: auto; white-space: pre-wrap; word-wrap: break-word; }
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@media screen and (max-width: 479px) {
pre { width: 280px; }
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<span><H1>Server Error in '/' Application.<hr width=100% size=1 color=silver></H1>
<h2> <i>Source stream is empty; it has a length of 0. No bytes, no data. We can't work with this.</i> </h2></span>
<font face="Arial, Helvetica, Geneva, SunSans-Regular, sans-serif ">
<b> Description: </b>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.
<br><br>
<b> Exception Details: </b>ImageResizer.ImageProcessingException: Source stream is empty; it has a length of 0. No bytes, no data. We can't work with this.<br><br>
<b>Source Error:</b> <br><br>
<table width=100% bgcolor="#ffffcc">
<tr>
<td>
<code>
An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.</code>
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<br>
<b>Stack Trace:</b> <br><br>
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<td>
<code><pre>
[ImageProcessingException (0x80004005): Source stream is empty; it has a length of 0. No bytes, no data. We can't work with this.]
ImageResizer.ImageBuilder.GetStreamFromSource(Object source, ResizeSettings settings, Boolean& disposeStream, String& path, Boolean& restoreStreamPosition) +806
ImageResizer.ImageBuilder.LoadImage(Object source, ResizeSettings settings, Boolean restoreStreamPos) +392
ImageResizer.ImageBuilder.BuildJob(ImageJob job) +183
ImageResizer.ImageBuilder.Build(ImageJob job) +242
ImageResizer.ImageBuilder.Build(Object source, Object dest, ResizeSettings settings, Boolean disposeSource, Boolean addFileExtension) +107
ImageResizer.ImageBuilder.Build(Object source, Object dest, ResizeSettings settings, Boolean disposeSource) +23
ImageResizer.ImageBuilder.Build(Object source, Object dest, ResizeSettings settings) +18
ImageResizer.<>c__DisplayClass3.<HandleRequest>b__2(Stream stream) +151
ImageResizer.Plugins.DiskCache.<>c__DisplayClasse.<TryWriteFile>b__d() +322
ImageResizer.Plugins.DiskCache.LockProvider.TryExecute(String key, Int32 timeoutMs, LockCallback success) +333
ImageResizer.Plugins.DiskCache.CustomDiskCache.TryWriteFile(CacheResult result, String physicalPath, String relativePath, ResizeImageDelegate writeCallback, DateTime sourceModifiedUtc, Int32 timeoutMs, Boolean recheckFS) +402
ImageResizer.Plugins.DiskCache.CustomDiskCache.GetCachedFile(String keyBasis, String extension, ResizeImageDelegate writeCallback, DateTime sourceModifiedUtc, Int32 timeoutMs, Boolean asynchronous) +733
ImageResizer.Plugins.DiskCache.DiskCache.Process(IResponseArgs e) +170
ImageResizer.Plugins.DiskCache.DiskCache.Process(HttpContext context, IResponseArgs e) +35
ImageResizer.InterceptModule.HandleRequest(HttpContext context, String virtualPath, NameValueCollection queryString, IVirtualFile vf) +1491
ImageResizer.InterceptModule.CheckRequest_PostAuthorizeRequest(Object sender, EventArgs e) +870
System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +136
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +69
</pre></code>
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<hr width=100% size=1 color=silver>
<b>Version Information:</b> Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.34209
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<!--
[ImageProcessingException]: Source stream is empty; it has a length of 0. No bytes, no data. We can't work with this.
at ImageResizer.ImageBuilder.GetStreamFromSource(Object source, ResizeSettings settings, Boolean& disposeStream, String& path, Boolean& restoreStreamPosition)
at ImageResizer.ImageBuilder.LoadImage(Object source, ResizeSettings settings, Boolean restoreStreamPos)
at ImageResizer.ImageBuilder.BuildJob(ImageJob job)
at ImageResizer.ImageBuilder.Build(ImageJob job)
at ImageResizer.ImageBuilder.Build(Object source, Object dest, ResizeSettings settings, Boolean disposeSource, Boolean addFileExtension)
at ImageResizer.ImageBuilder.Build(Object source, Object dest, ResizeSettings settings, Boolean disposeSource)
at ImageResizer.ImageBuilder.Build(Object source, Object dest, ResizeSettings settings)
at ImageResizer.InterceptModule.<>c__DisplayClass3.<HandleRequest>b__2(Stream stream)
at ImageResizer.Plugins.DiskCache.CustomDiskCache.<>c__DisplayClasse.<TryWriteFile>b__d()
at ImageResizer.Plugins.DiskCache.LockProvider.TryExecute(String key, Int32 timeoutMs, LockCallback success)
at ImageResizer.Plugins.DiskCache.CustomDiskCache.TryWriteFile(CacheResult result, String physicalPath, String relativePath, ResizeImageDelegate writeCallback, DateTime sourceModifiedUtc, Int32 timeoutMs, Boolean recheckFS)
at ImageResizer.Plugins.DiskCache.CustomDiskCache.GetCachedFile(String keyBasis, String extension, ResizeImageDelegate writeCallback, DateTime sourceModifiedUtc, Int32 timeoutMs, Boolean asynchronous)
at ImageResizer.Plugins.DiskCache.DiskCache.Process(IResponseArgs e)
at ImageResizer.Plugins.DiskCache.DiskCache.Process(HttpContext context, IResponseArgs e)
at ImageResizer.InterceptModule.HandleRequest(HttpContext context, String virtualPath, NameValueCollection queryString, IVirtualFile vf)
at ImageResizer.InterceptModule.CheckRequest_PostAuthorizeRequest(Object sender, EventArgs e)
at System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)
-->
修改
实际上，如果文件不存在，我想不向客户发送任何内容。
答案 0 :(得分：2)
问题似乎是你要返回Null Stream而不是null。
差异很微妙，但Stream.Null不是null，它是一个长度为0的实际流（也就是一个绝对空的流）。这就是你得到这个例外的原因。简而言之：
Stream.Null != null
您的虚拟提供程序应该返回null，如下所示：
if (!File.Exists(absoluteFilePath)) return null;
如果您检查source code，在第253行，您会看到ImageResizer在您返回null时抛出FileNotFoundException。如何处理此异常取决于其他几个因素，但在大多数配置中，这意味着用户将收到适当的404 HTTP响应。
答案 1 :(得分：0)
IVirtualImageProvider具有FileExists方法，并带有以下签名：
bool FileExists(string virtualPath, NameValueCollection queryString)
我必须正确实施它。如果它返回false，ImageResizer将返回任何内容，没有找到未找到文件的任何例外。