Date: Sun, 30 May 2010 01:57:57 -0400
From: Christopher Faylor <cgf-use-the-mailinglist-please AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: Reading /proc/registry/... returns extra char
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On Sun, May 30, 2010 at 12:15:15AM +0400, Andrey Repin wrote:
>Greetings, Corinna Vinschen!
>
>>> >> > $ cat >a.dat
>>> >> > /proc/registry/HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Control/Syst
>>> >> > emBootDevice
>>> 
>>> > This trailing NUL character was always there, already with Cygwin 1.5.
>>> > It's part of the file content.  If strings are stored with a trailing
>>> > NUL in a file, you don't want Cygwin to remove it for you, right?
>>> 
>>> Wrong. The training NULL is a string value terminator for REG_SZ variables,
>>> also a string separator for REG_MULTI_SZ ones. (Which ends with a spare NULL)
>>> It must not be exposed to the user.
>
>> I disagree.  When you're using tools like regtool, you're right.  But
>> when accessing the registry as *files* via the virtual /proc filesystem,
>> you want the file content.
>
>Yep. And I certainly not expect the NULL in text files. You know, not every
>console program is binary-safe when working with STDIO? Not even cygwin, as we
>can see in this thread.
>
>> And the file contains the trailing NUL in REG_SZ and REG_EXPAND_SZ values,
>> and multiple NULs in REG_MULTI_SZ values.
>
>That's right and true, when you're working with interface directly, but... all
>the programs I've used in the past, and all the interfaces, they do not expose
>trailing NULL to the client application.
>In this case, /proc/registry is an interface, but cat is the application.

NAME
       cat - concatenate files and print on the standard output

I don't see anything in cat's description which claims it should know
that some files are special and should be handled differently.

>> What do you suppose Cygwin should do with the NULs in REG_MULTI_SZ values?
>> Just remove them?
>
>Convert them to appropriate EOL sequences. And back to NULL's on write. As per
>definition of a text as "multiple strings".
>You don't need to argue over it, just document it properly :)

Converting a NUL to a EOL would be very strange behavior.  I don't think you
really know what you're asking for.

cgf

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