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

Your example works for me in LinqPad. Maybe use UriKind.Absolute? See also http://stackoverflow.com/questions/4161247/uri-trycreate-returns-true-for-any-string-value — Greg, Jun 17 '16 at 12:48
@Greg in my case though it throws a NullReferenceException in Uri.CreateUriInfo. Which .NET version did you use for the test? — Panagiotis Kanavos, Jun 17 '16 at 12:49
The .NET version is actually the *MOST* important information in this question. Please *don't* remove it, this is vandalism — Panagiotis Kanavos, Jun 17 '16 at 12:53
I can reproduce for 4.5+. Since 4.0 is no longer supported, this means the bug affect all modern versions. — Panagiotis Kanavos, Jun 17 '16 at 12:57
Throws an exception for any non ascii character it seems, e.g. ö or 日 — Greg, Jun 17 '16 at 12:57
Breaking change in 4.5.2 http://stackoverflow.com/questions/12004214/system-uri-tostring-behaviour-change-after-vs2012-install and https://msdn.microsoft.com/en-us/library/hh367887.aspx#core — Greg, Jun 17 '16 at 12:59
@Greg these changes aren't supposed to throw an unrelated exception though. `TryCreate` should return `false` in this case. This *is* a bug — Panagiotis Kanavos, Jun 17 '16 at 13:04
https://connect.microsoft.com/VisualStudio/feedback/details/778454/breaking-change-to-uri-iswellformeduristring-in-net-4-5 — Greg, Jun 17 '16 at 13:06
I opened a bug ticket as well: https://connect.microsoft.com/VisualStudio/feedback/details/2826777 — Selman Genç, Jun 17 '16 at 13:13
@SelmanGenç when you post Connect issues they should be as detailed as possible. You have to make it so that whoever triages the issue *can't* dismiss it out of hand. Even well written issues get ignored all the time. The canned response sounds too much like a dismissal — Panagiotis Kanavos, Jun 17 '16 at 13:31
@PanagiotisKanavos okey, this is my first time :) I will try to be more detailed in the future. — Selman Genç, Jun 17 '16 at 13:47

score 7 · Accepted Answer · answered Jun 17 '16 at 14:05

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.

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

1 Answers1