【51CTO独家特稿】在ASP.NET中通过HTTP上传大文件是一个由来已久的挑战,它是许多活跃的ASP.NET论坛最常讨论的问题之一,除了处理大文件外,用户还经常被要求要显示出文件上传的进度,当你需要直接控制从浏览器上传数据流时,你会四处碰壁。51CTO.com之前就曾针对性的报道过《解除ASP.NET上传文件的大小限制》和《ASP.NET大文件上传开发总结》等文章。
绝大多数人认为在ASP.NET中上传大文件有以下这些解决方案:
◆不要这样做。你***是在页面中嵌入一个Silverlight或Flash进程上传文件。
◆不要这样做。因为HTTP本身设计就不是为了上传大文件,重新思考你要的功能。
◆不要这样做。ASP.NET本身设计***也就能处理2GB大小的文件。
◆购买商业产品,如SlickUpload,它使用了一个HttpModule实现了文件流分块。
◆使用开源产品,如NeatUpload,它使用了一个HttpModule实现了文件流分块。
最近我接到一个任务,需构建一个上传工具实现以下功能:
◆必须工作在HTTP协议
◆必须允许非常大的文件上传(会大于2GB)
◆必须允许断点续传
◆必须允许并行上传
因此前三个解决方案都不适应我的需求,其它解决方案对于我而言又太笨重了,因此我开始着手解决在ASP.NET MVC中的这个问题,如果有这方面的开发背景,你一定了解大部分问题最终都归结于对ASP.NET输入流和连锁请求过程的控制,网上的资料一般都是这样描述的,只要你的代码访问了HttpRequest的InputStream属性,在你访问流之前,ASP.NET就会缓存整个上传的文件,这就意味着当我向云服务上传文件时,我必须等待整个大文件抵达服务器,然后才能将其传输到预定目的地,这意味着需要两倍的时间。
首先,我们推荐你阅读一下Scott Hanselman的有关ASP.NET MVC文件上传文章,地址http://www.hanselman.com/blog/CommentView.aspx?guid=bc137b6b-d8d0-47d1-9795-f8814f7d1903,先对文件上传有一个大致的了解,但Scott Hanselman的方法是不能上传大文件的,根据Scott Hanselman的方法,你只需要修改一下web.config文件,确保ASP.NET允许***支持2GB大小的文件上传,不要担心,这样设置并不会吃掉你的内存,因为凡是大于256KB的数据都被缓存到磁盘上去了。
- ﹤system.web﹥
- ﹤httpruntime requestlengthdiskthreshold="256" maxrequestlength="2097151"﹥
- ﹤/httpruntime﹥﹤/system.web﹥
这是一个简单的适合大多数应用的解决办法,但我的任务中不能借用这种方法,即使会将数据缓存到磁盘中,但这种类似于另存为的方法也会使用大量的内存。
图 1 :通过缓存整个文件,然后另存为的方式会使内存消耗突然上升
那么在ASP.NET MVC中通过直接访问流,不触发任何缓存机制,上传大文件该如何实现呢?解决办法就是尽量远离ASP.NET,我们先来看一看UploadController,它有三个行为方法,一个是索引我们上传的文件,一个是前面讨论的缓存逻辑,另一个是基于实时流的方法。
- public class UploadController : Controller
- {
- [AcceptVerbs(HttpVerbs.Get)]
- [Authorize]
- public ActionResult Index()
- {
- return View();
- }
- [AcceptVerbs(HttpVerbs.Post)]
- public ActionResult BufferToDisk()
- {
- var path = Server.MapPath("~/Uploads");
- foreach (string file in Request.Files)
- {
- var fileBase = Request.Files[file];
- try
- {
- if (fileBase.ContentLength > 0)
- {
- fileBase.SaveAs(Path.Combine(path, fileBase.FileName));
- }
- }
- catch (IOException)
- {
- }
- }
- return RedirectToAction("Index", "Upload");
- }
- //[AcceptVerbs(HttpVerbs.Post)]
- //[Authorize]
- public void LiveStream()
- {
- var path = Server.MapPath("~/Uploads");
- var context = ControllerContext.HttpContext;
- var provider = (IServiceProvider)context;
- var workerRequest = (HttpWorkerRequest)provider.GetService(typeof(HttpWorkerRequest));
- //[AcceptVerbs(HttpVerbs.Post)]
- var verb = workerRequest.GetHttpVerbName();
- if(!verb.Equals("POST"))
- {
- Response.StatusCode = (int)HttpStatusCode.NotFound;
- Response.SuppressContent = true;
- return;
- }
- //[Authorize]
- if(!context.User.Identity.IsAuthenticated)
- {
- Response.StatusCode = (int)HttpStatusCode.Unauthorized;
- Response.SuppressContent = true;
- return;
- }
- var encoding = context.Request.ContentEncoding;
- var processor = new UploadProcessor(workerRequest);
- processor.StreamToDisk(context, encoding, path);
- //return RedirectToAction("Index", "Upload");
- Response.Redirect(Url.Action("Index", "Upload"));
- }
- }
虽然这里明显缺少一两个类,但基本的方法还是讲清楚了,看起来和缓存逻辑并没有太大的不同之处,我们仍然将流缓存到了磁盘,但具体处理方式却有些不同了,首先,没有与方法关联的属性,谓词和授权限制都被移除了,使用手动等值取代了,使用手工响应操作而不用ActionFilterAttribute声明的原因是这些属性涉及到了一些重要的ASP.NET管道代码,实际上在我的代码中,我还特意拦截了原生态的HttpWorkerRequest,因为它不能同时做两件事情。
#p#
HttpWorkerRequest有VIP访问传入的请求,通常它是由ASP.NET本身支持工作的,但我们绑架了请求,然后欺骗剩下的请求,让它们误以为前面的请求已经全部得到处理,为了做到这一点,我们需要上面例子中未出现的UploadProcessor类,这个类的职责是物理读取来自浏览器的每个数据块,然后将其保存到磁盘上,因为上传的内容被分解成多个部分,UploadProcessor类需要找出内容头,然后拼接成带状数据输出,这一可以在一个上传中同时上传多个文件。
- internal class UploadProcessor
- {
- private byte[] _buffer;
- private byte[] _boundaryBytes;
- private byte[] _endHeaderBytes;
- private byte[] _endFileBytes;
- private byte[] _lineBreakBytes;
- private const string _lineBreak = "\r\n";
- private readonly Regex _filename =
- new Regex(@"Content-Disposition:\s*form-data\s*;\s*name\s*=\s*""file""\s*;\s*filename\s*=\s*""(.*)""",
- RegexOptions.IgnoreCase | RegexOptions.Compiled);
- private readonly HttpWorkerRequest _workerRequest;
- public UploadProcessor(HttpWorkerRequest workerRequest)
- {
- _workerRequest = workerRequest;
- }
- public void StreamToDisk(IServiceProvider provider, Encoding encoding, string rootPath)
- {
- var buffer = new byte[8192];
- if (!_workerRequest.HasEntityBody())
- {
- return;
- }
- var total = _workerRequest.GetTotalEntityBodyLength();
- var preloaded = _workerRequest.GetPreloadedEntityBodyLength();
- var loaded = preloaded;
- SetByteMarkers(_workerRequest, encoding);
- var body = _workerRequest.GetPreloadedEntityBody();
- if (body == null) // IE normally does not preload
- {
- body = new byte[8192];
- preloaded = _workerRequest.ReadEntityBody(body, body.Length);
- loaded = preloaded;
- }
- var text = encoding.GetString(body);
- var fileName = _filename.Matches(text)[0].Groups[1].Value;
- fileName = Path.GetFileName(fileName); // IE captures full user path; chop it
- var path = Path.Combine(rootPath, fileName);
- var files = new List {fileName};
- var stream = new FileStream(path, FileMode.Create);
- if (preloaded > 0)
- {
- stream = ProcessHeaders(body, stream, encoding, preloaded, files, rootPath);
- }
- // Used to force further processing (i.e. redirects) to avoid buffering the files again
- var workerRequest = new StaticWorkerRequest(_workerRequest, body);
- var field = HttpContext.Current.Request.GetType().GetField("_wr", BindingFlags.NonPublic | BindingFlags.Instance);
- field.SetValue(HttpContext.Current.Request, workerRequest);
- if (!_workerRequest.IsEntireEntityBodyIsPreloaded())
- {
- var received = preloaded;
- while (total - received >= loaded && _workerRequest.IsClientConnected())
- {
- loaded = _workerRequest.ReadEntityBody(buffer, buffer.Length);
- stream = ProcessHeaders(buffer, stream, encoding, loaded, files, rootPath);
- received += loaded;
- }
- var remaining = total - received;
- buffer = new byte[remaining];
- loaded = _workerRequest.ReadEntityBody(buffer, remaining);
- stream = ProcessHeaders(buffer, stream, encoding, loaded, files, rootPath);
- }
- stream.Flush();
- stream.Close();
- stream.Dispose();
- }
- private void SetByteMarkers(HttpWorkerRequest workerRequest, Encoding encoding)
- {
- var contentType = workerRequest.GetKnownRequestHeader(HttpWorkerRequest.HeaderContentType);
- var bufferIndex = contentType.IndexOf("boundary=") + "boundary=".Length;
- var boundary = String.Concat("--", contentType.Substring(bufferIndex));
- _boundaryBytes = encoding.GetBytes(string.Concat(boundary, _lineBreak));
- _endHeaderBytes = encoding.GetBytes(string.Concat(_lineBreak, _lineBreak));
- _endFileBytes = encoding.GetBytes(string.Concat(_lineBreak, boundary, "--", _lineBreak));
- _lineBreakBytes = encoding.GetBytes(string.Concat(_lineBreak + boundary + _lineBreak));
- }
- private FileStream ProcessHeaders(byte[] buffer, FileStream stream, Encoding encoding, int count, ICollection files, string rootPath)
- {
- buffer = AppendBuffer(buffer, count);
- var startIndex = IndexOf(buffer, _boundaryBytes, 0);
- if (startIndex != -1)
- {
- var endFileIndex = IndexOf(buffer, _endFileBytes, 0);
- if (endFileIndex != -1)
- {
- var precedingBreakIndex = IndexOf(buffer, _lineBreakBytes, 0);
- if (precedingBreakIndex > -1)
- {
- startIndex = precedingBreakIndex;
- }
- endFileIndex += _endFileBytes.Length;
- var modified = SkipInput(buffer, startIndex, endFileIndex, ref count);
- stream.Write(modified, 0, count);
- }
- else
- {
- var endHeaderIndex = IndexOf(buffer, _endHeaderBytes, 0);
- if (endHeaderIndex != -1)
- {
- endHeaderIndex += _endHeaderBytes.Length;
- var text = encoding.GetString(buffer);
- var match = _filename.Match(text);
- var fileName = match != null ? match.Groups[1].Value : null;
- fileName = Path.GetFileName(fileName); // IE captures full user path; chop it
- if (!string.IsNullOrEmpty(fileName) && !files.Contains(fileName))
- {
- files.Add(fileName);
- var filePath = Path.Combine(rootPath, fileName);
- stream = ProcessNextFile(stream, buffer, count, startIndex, endHeaderIndex, filePath);
- }
- else
- {
- var modified = SkipInput(buffer, startIndex, endHeaderIndex, ref count);
- stream.Write(modified, 0, count);
- }
- }
- else
- {
- _buffer = buffer;
- }
- }
- }
- else
- {
- stream.Write(buffer, 0, count);
- }
- return stream;
- }
- private static FileStream ProcessNextFile(FileStream stream, byte[] buffer, int count, int startIndex, int endIndex, string filePath)
- {
- var fullCount = count;
- var endOfFile = SkipInput(buffer, startIndex, count, ref count);
- stream.Write(endOfFile, 0, count);
- stream.Flush();
- stream.Close();
- stream.Dispose();
- stream = new FileStream(filePath, FileMode.Create);
- var startOfFile = SkipInput(buffer, 0, endIndex, ref fullCount);
- stream.Write(startOfFile, 0, fullCount);
- return stream;
- }
- private static int IndexOf(byte[] array, IList value, int startIndex)
- {
- var index = 0;
- var start = Array.IndexOf(array, value[0], startIndex);
- if (start == -1)
- {
- return -1;
- }
- while ((start + index) < array.Length)
- {
- if (array[start + index] == value[index])
- {
- index++;
- if (index == value.Count)
- {
- return start;
- }
- }
- else
- {
- start = Array.IndexOf(array, value[0], start + index);
- if (start != -1)
- {
- index = 0;
- }
- else
- {
- return -1;
- }
- }
- }
- return -1;
- }
- private static byte[] SkipInput(byte[] input, int startIndex, int endIndex, ref int count)
- {
- var range = endIndex - startIndex;
- var size = count - range;
- var modified = new byte[size];
- var modifiedCount = 0;
- for (var i = 0; i < input.Length; i++)
- {
- if (i >= startIndex && i < endIndex)
- {
- continue;
- }
- if (modifiedCount >= size)
- {
- break;
- }
- modified[modifiedCount] = input[i];
- modifiedCount++;
- }
- input = modified;
- count = modified.Length;
- return input;
- }
- private byte[] AppendBuffer(byte[] buffer, int count)
- {
- var input = new byte[_buffer == null ? buffer.Length : _buffer.Length + count];
- if (_buffer != null)
- {
- Buffer.BlockCopy(_buffer, 0, input, 0, _buffer.Length);
- }
- Buffer.BlockCopy(buffer, 0, input, _buffer == null ? 0 : _buffer.Length, count);
- _buffer = null;
- return input;
- }
- }
在处理代码的中间位置,你应该注意到了另一个类StaticWorkerRequest,这个类负责欺骗ASP.NET,在点击提交按钮时,它欺骗ASP.NET,让他认为没有文件上传,这是必需的,因为当上传完毕时,如果我们要重定向到所需的页面时,ASP.NET将会检查到在HTTP实体主体中仍然有数据,然后会尝试缓存整个上传,于是我们兜了一圈又回到了原点,为了避免这种情况,我们必须欺骗HttpWorkerRequest,将它注入到HttpContext中,获得请求开始部分的StaticWorkerRequest,它是唯一有用的数据。
- internal class StaticWorkerRequest : HttpWorkerRequest
- {
- readonly HttpWorkerRequest _request;
- private readonly byte[] _buffer;
- public StaticWorkerRequest(HttpWorkerRequest request, byte[] buffer)
- {
- _request = request;
- _buffer = buffer;
- }
- public override int ReadEntityBody(byte[] buffer, int size)
- {
- return 0;
- }
- public override int ReadEntityBody(byte[] buffer, int offset, int size)
- {
- return 0;
- }
- public override byte[] GetPreloadedEntityBody()
- {
- return _buffer;
- }
- public override int GetPreloadedEntityBody(byte[] buffer, int offset)
- {
- Buffer.BlockCopy(_buffer, 0, buffer, offset, _buffer.Length);
- return _buffer.Length;
- }
- public override int GetPreloadedEntityBodyLength()
- {
- return _buffer.Length;
- }
- public override int GetTotalEntityBodyLength()
- {
- return _buffer.Length;
- }
- public override string GetKnownRequestHeader(int index)
- {
- return index == HeaderContentLength
- ? "0"
- : _request.GetKnownRequestHeader(index);
- }
- // All other methods elided, they're just passthrough
- }
使用StaticWorkerRequest建立虚假的声明,现在你可以在ASP.NET MVC中通过直接访问数据流上传大文件,使用这个代码作为开始,你可以很容易地保存过程数据,并使用Ajax调用另一个控制器行为展示其进度,将大文件缓存到一个临时区域,可以实现断点续传,不用再等待ASP.NET进程将整个文件缓存到磁盘上,同样,保存文件时也不用消耗另存为方法那么多的内存了。
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