return Ok(new { count = , size });}注意上⾯Action⽅法Post的参数名files，必须要和上传页⾯中的Input type="file"标签的name属性值⼀样。

⽤⽂件流 (⼤⽂件上传) 在介绍这个⽅法之前我们先来看看⼀个包含上传⽂件的Http请求是什么样⼦的：Content-Type=multipart/form-data; boundary=---------------------------99614912995-----------------------------99614912995Content-Disposition: form-data; name="SOMENAME"Formulaire de Quota-----------------------------99614912995Content-Disposition: form-data; name="OTHERNAME"SOMEDATA-----------------------------99614912995Content-Disposition: form-data; name="files"; filename="Misc "SDFESDSDSDJXCK+DSDSDSSDSFDFDF423232DASDSDSDFDSFJHSIHFSDUIASUI+/==-----------------------------99614912995Content-Disposition: form-data; name="files"; filename="Misc "ASAADSDSDJXCKDSDSDSHAUSAUASAASSDSDFDSFJHSIHFSDUIASUI+/==-----------------------------99614912995Content-Disposition: form-data; name="files"; filename="Misc "TGUHGSDSDJXCK+DSDSDSSDSFDFDSAOJDIOASSAADDASDASDASSADASDSDSDSDFDSFJHSIHFSDUIASUI+/==-----------------------------99614912995--这就是⼀个multipart/form-data格式的Http请求，我们可以看到第⼀⾏信息是Http header，这⾥我们只列出了Content-Type这⼀⾏Http header信息，这和我们在html页⾯中form标签上的enctype属性值⼀致，第⼀⾏中接着有⼀个boundary=---------------------------99614912995，boundary=后⾯的值是随机⽣成的，这个其实是在声明Http请求中表单数据的分隔符是什么，其代表的是在Http请求中每读到⼀⾏ ---------------------------99614912995，表⽰⼀个section数据，⼀个section有可能是⼀个表单的键值数据，也有可能是⼀个上传⽂件的⽂件数据。每个section的第⼀⾏是section header，其中Content-Disposition属性都为form-data，表⽰这个section来⾃form标签提交的表单数据，如果section header拥有filename或filenamestar属性，那么表⽰这个section是⼀个上传⽂件的⽂件数据，否者这个section是⼀个表单的键值数据，section header之后的⾏就是这个section真正的数据⾏。例如我们上⾯的例⼦中，前两个section就是表单键值对，后⾯三个section是三个上传的图⽚⽂件。

那么接下来，我们来看看怎么⽤⽂件流来上传⼤⽂件，避免⼀次性将所有上传的⽂件都加载到服务器内存中。⽤⽂件流来上传⽐较⿇烦的地⽅在于你⽆法使⽤ CoreMVC的模型绑定器来将上传⽂件反序列化为C#对象（如同前⾯介绍的IFormFile接⼝那样）。⾸先我们需要定义类MultipartRequestHelper，⽤于识别Http请求中的各个section类型（是表单键值对section，还是上传⽂件section）using System;using ;using s;namespace artRequest{ public static class MultipartRequestHelper { // Content-Type: multipart/form-data; boundary="----WebKitFormBoundarymx2fSWqWSd0OxQqq" // The spec says 70 characters is a reasonable limit. public static string GetBoundary(MediaTypeHeaderValue contentType, int lengthLimit) { //var boundary = Quotes(ry);// .NET Core <2.0 var boundary = Quotes(ry).Value; //.NET Core 2.0 if (OrWhiteSpace(boundary)) { throw new InvalidDataException("Missing content-type boundary."); } //注意这⾥的指的是boundary=---------------------------99614912995中等号后⾯---------------------------99614912995字符串的长度，也就是section分隔符的长度，上⾯也说了这个长度⼀般不会超过70个字符是⽐较合理的 if ( > lengthLimit) { throw new InvalidDataException( $"Multipart boundary length limit {lengthLimit} exceeded."); } return boundary; } public static bool IsMultipartContentType(string contentType) { return !OrEmpty(contentType) && f("multipart/", lIgnoreCase) >= 0; } //如果section是表单键值对section，那么本⽅法返回true public static bool HasFormDataContentDisposition(ContentDispositionHeaderValue contentDisposition) { // Content-Disposition: form-data; name="key"; return contentDisposition != null && ("form-data") && OrEmpty() // For .NET Core <2.0 remove ".Value" && OrEmpty(); // For .NET Core <2.0 remove ".Value" } //如果section是上传⽂件section，那么本⽅法返回true public static bool HasFileContentDisposition(ContentDispositionHeaderValue contentDisposition) { // Content-Disposition: form-data; name="myfile1"; filename="Misc " return contentDisposition != null && ("form-data") && (!OrEmpty() // For .NET Core <2.0 remove ".Value" || !OrEmpty()); // For .NET Core <2.0 remove ".Value" } // 如果⼀个section的Header是： Content-Disposition: form-data; name="files"; filename="Misc " // 那么本⽅法返回： files public static string GetFileContentInputName(ContentDispositionHeaderValue contentDisposition) { return ; } // 如果⼀个section的Header是： Content-Disposition: form-data; name="myfile1"; filename="Misc " // 那么本⽅法返回： Misc public static string GetFileName(ContentDispositionHeaderValue contentDisposition) { return ; } }}然后我们需要定义⼀个扩展类叫FileStreamingHelper，其中的StreamFiles扩展⽅法⽤于读取上传⽂件的⽂件流数据，并且将数据写⼊到服务器的硬盘上，其接受⼀个参数targetDirectory，⽤于声明将上传⽂件存储到服务器的哪个⽂件夹下。using ;using es;using inding;using lities;using s;using System;using ization;using ;using ;using ;namespace artRequest{ public static class FileStreamingHelper { private static readonly FormOptions _defaultFormOptions = new FormOptions(); public static async Task StreamFiles(this HttpRequest request, string targetDirectory) { if (!ipartContentType(tType)) { throw new Exception($"Expected a multipart request, but got {tType}"); } // Used to accumulate all the form url encoded key value pairs in the

// request. var formAccumulator = new KeyValueAccumulator(); var boundary = ndary( (tType), _artBoundaryLengthLimit); var reader = new MultipartReader(boundary, ); var section = await xtSectionAsync();//⽤于读取Http请求中的第⼀个section数据 while (section != null) { ContentDispositionHeaderValue contentDisposition; var hasContentDispositionHeader = se(tDisposition, out contentDisposition); if (hasContentDispositionHeader) { /* ⽤于处理上传⽂件类型的的section -----------------------------99614912995 Content - Disposition: form - data; name = "files"; filename = "Misc " ASAADSDSDJXCKDSDSDSHAUSAUASAASSDSDFDSFJHSIHFSDUIASUI+/== -----------------------------99614912995 */ if (eContentDisposition(contentDisposition)) { if (!(targetDirectory)) { Directory(targetDirectory); } var fileName = eName(contentDisposition); var loadBufferBytes = 1024;//这个是每⼀次从Http请求的section中读出⽂件数据的⼤⼩，单位是Byte即字节，这⾥设置为1024的意思是，每次从Http请求的section数据流中读取出1024字节的数据到服务器内存中，然后写⼊下⾯targ using (var targetFileStream = (targetDirectory + "" + fileName)) { //是类型，表⽰的是Http请求中⼀个section的数据流，从该数据流中可以读出每⼀个section的全部数据，所以我们下⾯也可以不⽤Async⽅法，⽽是在⼀个循环中⽤ await Async(targetFileStream, loadBufferBytes); } } /* ⽤于处理表单键值数据的section -----------------------------99614912995 Content - Disposition: form - data; name = "SOMENAME" Formulaire de Quota -----------------------------99614912995 */ else if (mDataContentDisposition(contentDisposition)) { // Content-Disposition: form-data; name="key" // // value // Do not limit the key name length here because the

// multipart headers length limit is already in effect. var key = Quotes(); var encoding = GetEncoding(section); using (var streamReader = new StreamReader( , encoding, detectEncodingFromByteOrderMarks: true, bufferSize: 1024, leaveOpen: true)) { // The value length limit is enforced by MultipartBodyLengthLimit var value = await EndAsync(); if ((value, "undefined", lIgnoreCase)) { value = ; } (, value); // For .NET Core <2.0 remove ".Value" from key if (ount > _ountLimit) { throw new InvalidDataException($"Form key count limit {_ountLimit} exceeded."); } } } } // Drains any remaining section body that has not been consumed and // reads the headers for the next section. section = await xtSectionAsync();//⽤于读取Http请求中的下⼀个section数据 } // Bind form data to a model var formValueProvider = new FormValueProvider( , new FormCollection(ults()), tCulture); return formValueProvider; } private static Encoding GetEncoding(MultipartSection section) { MediaTypeHeaderValue mediaType; var hasMediaTypeHeader = se(tType, out mediaType); // UTF-7 is insecure and should not be honored. UTF-8 will succeed in

// most cases. if (!hasMediaTypeHeader || (ng)) { return 8; } return ng; } }}现在我们还需要创建⼀个 Core MVC的⾃定义拦截器DisableFormValueModelBindingAttribute，该拦截器实现接⼝IResourceFilter，⽤来禁⽤ Core MVC的模型绑定器，这样当⼀个Http请求到达服务器后， Core MVC就不会在将请求的所有上传⽂件数据都加载到服务器内存后，才执⾏Contoller的Action⽅法，⽽是当Http请求到达服务器时，就⽴刻执⾏Contoller的Action⽅法。[AttributeUsage( | )]public class DisableFormValueModelBindingAttribute : Attribute, IResourceFilter{ public void OnResourceExecuting(ResourceExecutingContext context) { var formValueProviderFactory = roviderFactories .OfType() .FirstOrDefault(); if (formValueProviderFactory != null) { (formValueProviderFactory); }

var jqueryFormValueProviderFactory = roviderFactories .OfType() .FirstOrDefault(); if (jqueryFormValueProviderFactory != null) { (jqueryFormValueProviderFactory); } }

public void OnResourceExecuted(ResourceExecutedContext context) { }}最后我们在Contoller中定义⼀个叫Index的Action⽅法，并注册我们定义的DisableFormValueModelBindingAttribute拦截器，来禁⽤Action的模型绑定。Index⽅法会调⽤我们前⾯定义的FileStreamingHelper类中的StreamFiles⽅法，其参数为⽤来存储上传⽂件的⽂件夹路径。StreamFiles⽅法会返回⼀个FormValueProvider，⽤来存储Http请求中的表单键值数据，之后我们会将其绑定到MVC的视图模型viewModel上，然后将viewModel传回给客户端浏览器，来告述客户端浏览器⽂件上传成功。[HttpPost][DisableFormValueModelBinding]public async Task Index(){ FormValueProvider formModel; formModel = await Files(@"D:UploadingFiles"); var viewModel = new MyViewModel(); var bindingSuccessful = await TryUpdateModelAsync(viewModel, prefix: "", valueProvider: formModel); if (!bindingSuccessful) { if (!d) { return BadRequest(ModelState); } } return Ok(viewModel);}视图模型viewModel的定义如下：public class MyViewModel{ public string Username { get; set; }}最后我们⽤于上传⽂件的html页⾯和前⾯⼏乎⼀样：