通过POST以文件上载/分段形式使用REST WebService

Question

I have a REST webservice method created using Django, which processes/handles file upload. How do I consume it from my windows-form/desktop application using C#? In addition, can someone explain how can I do dictionary parameter passing in C#, like the below python snippet code?

import requests
url = "http://<url>
files = {'file' : open("<filename>", "rb").read(), 'name':'sample.txt'}
r = requests.post(url, files)

Answer 1

If you can use DNF45 then MultipartFormDataContent will do most of the heavy lifting for you. The following sample uploads a photo to picpaste mimicking a form post. Then it uses HtmlAgility to pick apart the response which is going a lot further than you asked but is a handy thing to be able to do when you have to use interactive web pages as though they were web services.

Obviously you have to change the file name to point at a picture on your own computer. This isn't supposed to be production grade, it was just me figuring out how to manipulate picpaste because I'm too cheap to pay for imgur.

using System;
using System.IO;
using System.Linq;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Net.Mime;

namespace picpaste1
{
  class Program
  {
    static void Main(string[] args)
    {
      var fi = new FileInfo(@"path\to\picture.png");
      using (var client = new HttpClient())
      using (var mfdc = new MultipartFormDataContent())
      using (var filestream = fi.OpenRead())
      using (var filecontent = new StreamContent(filestream))
      {

        filecontent.Headers.ContentDisposition = 
          new ContentDispositionHeaderValue(DispositionTypeNames.Attachment)
        {
          FileName = fi.Name,
          Name = "upload"
        };
        filecontent.Headers.ContentType = new MediaTypeHeaderValue("image/png");

        mfdc.Add(new StringContent("7168000"), "MAX_FILE_SIZE");
        mfdc.Add(filecontent);
        mfdc.Add(new StringContent("9"), "storetime");
        mfdc.Add(new StringContent("no"), "addprivacy");
        mfdc.Add(new StringContent("yes"), "rules");
        var uri = "http://picpaste.com/upload.php";
        var res = client.PostAsync(uri, mfdc).Result;
        var doc = new HtmlAgilityPack.HtmlDocument();
        doc.LoadHtml(res.Content.ReadAsStringAsync().Result);
        uri = doc.DocumentNode.SelectNodes("//td/a").First()
          .GetAttributeValue("href","NOT FOUND");
        res = client.GetAsync(uri).Result;
        doc.LoadHtml(res.Content.ReadAsStringAsync().Result);
        var foo = doc.DocumentNode.SelectNodes("//div[@class='picture']/a").First()
          .GetAttributeValue("href","NOT FOUND");
        Console.WriteLine("http://picpaste.com{0}", foo);
        Console.ReadLine();
      }
    }
  }
}

If the response is JSON rather than HTML, which is likely for a web service, use the Newtonsoft.Json parser. There are tutorials all over the net. It's comprehensive and very fast, my weapon of choice. Broadly, you create classes to model the object graph you are expecting in the JSON and then use them to type a generic method call.

using Newtonsoft.Json;

var res = client.PostAsync(uri, mfdc).Result;
Foo foo = JsonConvert.DeserializeObject<Foo>(res.Content.ReadAsStringAsync().Result);

You can get both HtmlAgility and Newtonsoft.Json from NuGet.