[Mono-dev] Type.GUID patch

[Kornél Pál]

> From: Vladimir Lushnikov
>Can I ask a slightly unrelated question - does Mono actually generate
>unique GUID's at the moment? I use them for a generic collection of
>"worker" sockets in a server, so wondering if they are unique enough to be
>used there in Mono (I know it works in .NET).

GUID's are generated using the same concepts as in MS.NET. So you can use
Guid.NewGuid() in Mono as well. Note that we are talking about Type.GUID
property that is generated based on the type not randomly.

>From: Robert Jordan
>for the records: the automatically generated Type.GUID
>is a Version 3 UUID, see
>
>http://www.webdav.org/specs/draft-leach-uuids-guids-01.txt
>
>To generate a MS compatible Type.GUID we'd need the so
>called "name space ID" used by MS.

If you can figure out the exact algoryth used by MS.NET we can generate
Type.GUIDs. And I think performance isn't important for this property.

Kornél

----- Original Message -----
From: "Robert Jordan" <robertj at gmx.net>
To: <mono-devel-list at lists.ximian.com>
Sent: Saturday, September 03, 2005 11:45 PM
Subject: Re: [Mono-dev] Type.GUID patch


> Hi,
>
> for the records: the automatically generated Type.GUID
> is a Version 3 UUID, see
>
> http://www.webdav.org/specs/draft-leach-uuids-guids-01.txt
>
> To generate a MS compatible Type.GUID we'd need the so
> called "name space ID" used by MS.
>
> Rob
>
> Kornél Pál wrote:
>> This explains how GUIDs are generated but it doesn't mention the actual
>> hash
>> algorytm used to generate GUID from the mentioned components:
>>
>> http://blogs.msdn.com/adam_nathan/archive/2003/10/19/56779.aspx
>>
>> And GUID has a specification that should be followed when generating
>> GUIDs.
>> There are standard descriptions but this MS centric enough to can provide
>> compatiblity with MS.NET:
>>
>> http://msdn.microsoft.com/library/en-us/dnnetcomp/html/PPCGuidGen.asp
>>
>> Kornél
>>
>> ----- Original Message -----
>> From: "Kornél Pál" <kornelpal at hotmail.com>
>> To: <sebastien.pouliot at gmail.com>; "Robert Jordan" <robertj at gmx.net>
>> Cc: <mono-devel-list at lists.ximian.com>
>> Sent: Saturday, September 03, 2005 9:51 PM
>> Subject: Re: [Mono-dev] Type.GUID patch
>>
>>
>>> Hi,
>>>
>>> Type.GUID is useful only when using COM interop. Of course there may be
>>> other uses but I don't tink it is needed for anything else.
>>>
>>> GUIDs are identifiers in COM so I think we should not implement a
>>> different
>>> algorythm just to return some value. I think it's better to throw an
>>> exception for type that have no GuidAttribute instead of returning some
>>> forged value that is different from MS.NET type GUID.
>>>
>>> I think performance is not so important regarding this property as it is
>>> called rarely. But if we want to speed up GUID property it can be cached
>>> in
>>> a private field.
>>>
>>> Kornél
>>>
>>> ----- Original Message -----
>>> From: "Sebastien Pouliot" <sebastien.pouliot at gmail.com>
>>> To: "Robert Jordan" <robertj at gmx.net>
>>> Cc: <mono-devel-list at lists.ximian.com>
>>> Sent: Saturday, September 03, 2005 7:09 PM
>>> Subject: Re: [Mono-dev] Type.GUID patch
>>>
>>>
>>>> Hello Robert,
>>>>
>>>> On Sat, 2005-03-09 at 17:00 +0200, Robert Jordan wrote:
>>>>
>>>>> The hash appears to change with the assembly name and type name.
>>>>> Renaming gt.cs will return another GUID as well as renaming
>>>>> "App". Renaming gt.exe doesn't change the GUID.
>>>>> Applying an AssemblyVersionAttribute will change the GUID,
>>>>> so I'm pretty sure, that Type.AssemblyQualifiedName is taken
>>>>> into account while generating the hash.
>>>>>
>>>>> The following algorithm computes the GUID from
>>>>> Type.AssemblyQualifiedName using a MD5 hash:
>>>>>
>>>>> Guid ComputeGuid (Type t)
>>>>> {
>>>>>      byte[] bytes = System.Text.Encoding.UTF8.
>>>>>          GetBytes (t.AssemblyQualifiedName);
>>>>>      using (System.Security.Cryptography.MD5 md5 =
>>>>>             System.Security.Cryptography.MD5.Create ()) {
>>>>>          return new Guid (md5.ComputeHash (bytes));
>>>>>      }
>>>>> }
>>>>>
>>>>> Is it a patch worth?
>>>>
>>>>
>>>> I guess it depends on how it's gonna be used. This isn't the first time
>>>> people talks about Type.Guid but I never seen any talk about _using_
>>>> it ;-) at least not with Mono.
>>>>
>>>> MD5 will give you a 128 bits digest value, which match the required
>>>> Guid
>>>> length, and recent problems related to MD5 are pretty much irrelevant
>>>> to
>>>> such usage. So it's probably (if everything is included in the
>>>> qualified
>>>> name) a correct implementation - functionality-wise.
>>>>
>>>> But creating a using MD5 is kind of heavyweight - even more if a new
>>>> instance is created each time. So anyone using this heavily will notice
>>>> a big performance problem.
>>>> --
>>>> Sebastien Pouliot
>>>> email: sebastien at ximian.com
>>>> blog: http://pages.infinit.net/ctech/
>>>>
>>>> _______________________________________________
>>>> Mono-devel-list mailing list
>>>> Mono-devel-list at lists.ximian.com
>>>> http://lists.ximian.com/mailman/listinfo/mono-devel-list
>>>>
>>>
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>
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