UploadString期间System.Net.WebClient不引发错误无效的URL？ [英] System.Net.WebClient not throwing error during UploadString to invalid url?

问题描述

鉴于这种code，我期待一个例外的情况发生，但 System.Net .WebClient.UploadString 返回一个空字符串转化结果。

Given this code, I expected an exception to happen, but System.Net.WebClient.UploadString returns an empty string into result.

我oviously忽视的东西，但什么？

I'm oviously overlooking something, but what?

using System.Net;
using System.Text;

[TestClass()]
public class WebClientTests
{
    [TestMethod()]
    public void WebClientUploadStringToInvalidUrlTest()
    {
        var webClient = new WebClient { Encoding = Encoding.UTF8 };
        var result =  webClient.UploadString("{{foo-bar}}", "snafu");
        Assert.IsTrue(string.IsNullOrEmpty(result));
    }

    [TestMethod()]
    [ExpectedException(typeof(ArgumentNullException))]
    public void WebClientUploadStringToNullUrlTest()
    {
        var webClient = new WebClient { Encoding = Encoding.UTF8 };
        string url = null;
        var result = webClient.UploadString(url, "snafu");
        Assert.IsTrue(string.IsNullOrEmpty(result));
    }

}

修改的：作为<一个href="http://stackoverflow.com/questions/24082706/system-net-webclient-not-throwing-error-during-uploadstring-to-invalid-url?noredirect=1#comment37140208_24082706">per建议由汉诺增加了一个空测试以及的，而这将引发 ArgumentNullException 样的，我的预期。

edit: as per suggestion by hanno added a null test as well, and this throws an ArgumentNullException which I kind of expected.

推荐答案

这只能通过查看内部的实现细节，回答这个问题。

It is only possible to answer this by looking at internal implementation details.

在preparation的 WebClient的类尝试建立一个真正的从字符串你在超负荷<提供的乌里 HREF =htt​​p://msdn.microsoft.com/en-us/library/ms144236相对=nofollow> UploadString 。

In preparation the WebClient class tries to build an real Uri from the string you provided in that overload to UploadString.

在code大致是这样的，在4.0框架：

The code roughly looks like this in the 4.0 framework:

 if (!Uri.TryCreate(path, UriKind.Absolute, out address))
 {
      return new Uri(Path.GetFullPath(path));
 } 

借助 TryCreate 回报的虚假用于非的相对= nofollow的> 的URI路径一致，因此回落到创建一个乌里的的你的字符串，返回的Path.GetFullPath 的乌里与<一个HREF =htt​​ps://en.wikipedia.org/wiki/File_URI_scheme相对=nofollow>文件：//方案

The TryCreate returns false for your non URI conforming path so it falls back to creating an Uri for the Path.GetFullPath of your string, which returns an Uri with a file:// scheme.

内部的 Web客户端使用的WebRequest .Create ，以获得的WebRequest ，能够处理给定的方案。在你的情况下， FileWebRequest 将返回（因方案是文件：// ）

Internally the WebClient uses WebRequest.Create to obtain a WebRequest that is capable of handling the given scheme. In your case a FileWebRequest will be returned (due to the scheme being file://)

剥离后，以下简化调用序列执行乌里获得所有的检查和内部管道：

Stripping all checks and internal plumbing the following simplified call sequence is executed after the Uri is obtained:

        var fwr = (FileWebRequest) WebRequest.Create(new Uri(Path.GetFullPath(path)));
        fwr.Method ="POST";
        var us = fwr.GetRequestStream();
        var upload = Encoding.UTF8.GetBytes("snafu");
        us.Write(upload,0,upload.Length);
        us.Close();
        var sr = new StreamReader(fwr.GetResponse().GetResponseStream());
        return sr.ReadToEnd();

这并不抛出异常，并返回一个空字符串。

Which doesn't throw an exception and returns an empty string.

您设想的我希望这引发异常，的是错误的。

Your assumption "I expect this to throw an exception" is wrong.

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