Why doesn't System.Uri recognize query parameter for local file path?

问题

I need to add some additional query information to file path as query parameter to parse path later during files processing. I though that System.Uri class can help me with this, but it looks like it doesn't give me what I expected for local file paths.

var fileUri = new Uri("file:///c://a.txt?select=10")
// fileUri.AbsoluteUri = "file:///c://a.txt%3Fselect=10"
// fileUri.Query = ""

var httpUri = new Uri("http://someAddress/a.txt?select=10")
// httpUri.AbsoluteUri = "http://someaddress/a.txt?select=10"
// httpUri.Query = "?select=10"

In the case of "ftp://someAddress/a.txt?select=10" - query string is also empty

I understand that System.Uri probably resolves "a.txt?select=10" to correct file name "a.txt%3Fselect=10", but WHY - how to escape this?

Thanks in advance

回答1:

This is a bug which Microsoft won't fix : Bug 594562 As you can see they propose reflection as an workaround:

...
Console.WriteLine("Before");
Uri fileUri = new Uri("file://host/path/file?query#fragment");
Console.WriteLine("AbsoluteUri: " + fileUri.AbsoluteUri);
Console.WriteLine("ToString: " + fileUri.ToString());
Console.WriteLine("LocalPath: " + fileUri.LocalPath);
Console.WriteLine("Query: " + fileUri.Query);
Console.WriteLine("Fragment: " + fileUri.Fragment);

Type uriParserType = typeof(UriParser);
FieldInfo fileParserInfo = uriParserType.GetField("FileUri", BindingFlags.Static | BindingFlags.NonPublic);
UriParser fileParser = (UriParser)fileParserInfo.GetValue(null);
FieldInfo fileFlagsInfo = uriParserType.GetField("m_Flags", BindingFlags.NonPublic | BindingFlags.Instance);
int fileFlags = (int)fileFlagsInfo.GetValue(fileParser);
int mayHaveQuery = 0x20;
fileFlags |= mayHaveQuery;
fileFlagsInfo.SetValue(fileParser, fileFlags);

Console.WriteLine();
Console.WriteLine("After");
fileUri = new Uri("file://host/path/file?query#fragment");
Console.WriteLine("AbsoluteUri: " + fileUri.AbsoluteUri);
Console.WriteLine("ToString: " + fileUri.ToString());
Console.WriteLine("LocalPath: " + fileUri.LocalPath);
Console.WriteLine("Query: " + fileUri.Query);
Console.WriteLine("Fragment: " + fileUri.Fragment);  
...  

回答2:

Query string parameters are not valid when requesting a local file.

When you requests a file using http the file is executed and is therefore able to read and process the querystring. When you request a local file it is not executed and so is unable to make use of the querystring.

What is the reason you are adding querystring params to a file request? Is there another way of doing it?

来源：https://stackoverflow.com/questions/8757585/why-doesnt-system-uri-recognize-query-parameter-for-local-file-path