Why Uri.TryCreate throws NRE when url contains Turkish character?

Question

I have encountered an interesting situation where I get NRE from Uri.TryCreate method when it's supposed to return false.

You can reproduce the issue like below:

Uri url;
if (Uri.TryCreate("http:Ç", UriKind.RelativeOrAbsolute, out url))
{
    Console.WriteLine("success");
}

I guess it's failing during the parse, but when I try "http:A" for example, it returns true and parses it as relative url. Even if fails on parse it should just return false as I understand, what could be the problem here? This seems like a bug in the implementation cause documentation doesn't mention about any exception on this method.

The error occurs in .NET 4.6.1 but not 4.0

Answer 1

This is a bug in the .NET framework. You can open a ticket on MicrosoftConnect.

The exception will be raised in this method

void Systen.Uri.CreateUriInfo(System.Uri.Flags cF)

on line 2290 (inspect the reference source) executing following statement:

// This is NOT an ImplicitFile uri
idx = (ushort)m_Syntax.SchemeName.Length;

At this time, the m_Syntax object will be null, because during parsing, it will be discarded.

Method

void InitializeUri(ParsingError err, UriKind uriKind, out UriFormatException e)

line 121:

if (m_Syntax.IsSimple)
{
    if ((err = PrivateParseMinimal()) != ParsingError.None)
    {
        if (uriKind != UriKind.Absolute && err <= ParsingError.LastRelativeUriOkErrIndex)
        {
            // RFC 3986 Section 5.4.2 - http:(relativeUri) may be considered a valid relative Uri.
            m_Syntax = null; // convert to relative uri
            e = null;
            m_Flags &= Flags.UserEscaped; // the only flag that makes sense for a relative uri
         }
         // ...
     }
    // ...
 }

The PrivateParseMinimal() method returns ParsingError.BadAuthority and uriKind == UriKind.RelativeOrAbsolute by your specification.

The PrivateParseMinimal() method looks for any of the following character sequences: "//", "\", "/\", "/". And since there are no such sequences in your input string, a ParsingError.BadAuthority code will be returned.