asp.net-core – ASP.NET Core 1.1中的multipart / form-data(File

我正在尝试构建一个ASP.NET Core 1.1 Controller方法来处理如下所示的HTTP请求：

POST https://localhost/api/data/upload HTTP/1.1
Content-Type: multipart/form-data; boundary=--------------------------625450203542273177701444
Host: localhost
Content-Length: 474

----------------------------625450203542273177701444
Content-Disposition: form-data; name="file"; filename="myfile.txt"
Content-Type: text/plain

<< Contents of my file >>

----------------------------625450203542273177701444
Content-Disposition: form-data; name="text"
Content-Type: application/json

{"md5":"595f44fec1e92a71d3e9e77456ba80d0","sessionIds":["123","abc"]}
----------------------------625450203542273177701444--

它是一个multipart / form-data请求,其中一部分是(小)文件,另一部分是基于提供的规范的json blob.

理想情况下,我喜欢我的控制器方法看起来像：

[HttpPost]
public async Task Post(UploadPayload payload)
{
   // TODO
}

public class UploadPayload
{
    public IFormFile File { get; set; }

    [Required]
    [StringLength(32)]
    public string Md5 { get; set; }

    public List<string> SessionIds { get; set; }
}

但唉,这不是Just Work {TM}.当我这样时,IFormFile会填充,但json字符串不会反序列化到其他属性.

我还尝试向UploadPayload添加一个Text属性,该属性具有除IFormFile以外的所有属性,并且也不接收数据.例如.

public class UploadPayload
{
    public IFormFile File { get; set; }

    public UploadPayloadMetadata Text { get; set; }
}

public class UploadPayloadMetadata
{
    [Required]
    [StringLength(32)]
    public string Md5 { get; set; }

    public List<string> SessionIds { get; set; }
}

我的解决方法是避免模型绑定并使用MultipartReader：

[HttpPost]
public async Task Post()
{
   ...

   var reader = new MultipartReader(Request.GetMultipartBoundary(),HttpContext.Request.Body);

   var section = await reader.ReadNextSectionAsync();
   var filePart = section.AsFileSection();

   // Do stuff & things with the file

   section = await reader.ReadNextSectionAsync();
   var jsonPart = section.AsFormDataSection();
   var jsonString = await jsonPart.GetValueAsync();

   // Use $JsonLibrary to manually deserailize into the model
   // Do stuff & things with the metadata

   ...
}

做上面的操作绕过了模型验证功能等.另外,我想也许我可以把那个jsonString然后以某种方式让它进入一个状态,然后我可以调用等待TryUpdateModelAsync(payloadModel,…)但是无法弄清楚如何到那儿 – 这似乎也没那么干净.

是否有可能像我的第一次尝试一样达到我想要的“透明”模型绑定状态？如果是这样,那怎么会这样呢？

解决方法

const formData = new FormData();
formData.append(`file`,file);
formData.append('md5',JSON.stringify(md5));
formData.append('sessionIds',JSON.stringify(sessionIds));

执行此操作后,可以将[FromForm]属性添加到MD5属性以将其绑定,因为它是一个简单的字符串值.这不适用于SessionIds属性,因为它是一个复杂的对象.

可以使用自定义模型绑定器来完成从表单数据绑定复杂JSON：

public class FormDataJsonBinder : IModelBinder
{
    public Task BindModelAsync(ModelBindingContext bindingContext)
    {
        if(bindingContext == null) throw new ArgumentNullException(nameof(bindingContext));

        // Fetch the value of the argument by name and set it to the model state
        string fieldName = bindingContext.FieldName;
        var valueProviderResult = bindingContext.ValueProvider.GetValue(fieldName);
        if(valueProviderResult == ValueProviderResult.None) return Task.CompletedTask;
        else bindingContext.ModelState.SetModelValue(fieldName,valueProviderResult);

        // Do nothing if the value is null or empty
        string value = valueProviderResult.FirstValue;
        if(string.IsNullOrEmpty(value)) return Task.CompletedTask;

        try
        {
            // Deserialize the provided value and set the binding result
            object result = JsonConvert.DeserializeObject(value,bindingContext.ModelType);
            bindingContext.Result = ModelBindingResult.Success(result);
        }
        catch(JsonException)
        {
            bindingContext.Result = ModelBindingResult.Failed();
        }

        return Task.CompletedTask;
    }
}

然后,您可以在DTO类中使用ModelBinder属性来指示此绑定器应该用于绑定MyJson属性：

public class UploadPayload
{
    public IFormFile File { get; set; }

    [Required]
    [StringLength(32)]
    [FromForm]
    public string Md5 { get; set; }

    [ModelBinder(BinderType = typeof(FormDataJsonBinder))]
    public List<string> SessionIds { get; set; }
}

您可以在ASP.NET Core文档中阅读有关自定义模型绑定的更多信息：https://docs.microsoft.com/en-us/aspnet/core/mvc/advanced/custom-model-binding

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