From: Michael Selig <michael.selig@...>
Date: 2009-02-25T07:41:57+09:00
Subject: [ruby-core:22431] Re: [Feature #908] Should be an easy way of reading N characters from am I/O stream

Hi Michal,

On Wed, 25 Feb 2009 00:20:52 +1100, Michal Suchanek <hramrach@centrum.cz>  
wrote:

>>> BTW the same goes for "reading N bytes up to a character boundary"
>>> unless you are willing to accept that you might read nothing even if
>>> data is available because the character did not fit into N bytes, even
>>> for a large N.
>>
>> The current behaviour of IO#gets "limit" parameter is "read N bytes but
>> round *UP* to the next character boundary". Therefore you may get more  
>> bytes
>> returned than requested. As long as "limit" is 1 or more, you should  
>> always
>> read something unless the file is at EOF, right?
>>
>> However I still do not understand why reading N characters (instead of  
>> the
>> current "limit" implementation) might be described as being "insecure".  
>> Can
>> someone please explain it? It is clear that the string returned may be
>> larger than N bytes long, but why is that "insecure"?
>>
>
> The current gets is not any more secure since it rounds up. If you
> found a bug in an encoding that could give you an infinite character
> either version would break.

Actually rounding *up* to the character boundary *is* more secure. You  
pointed it out yourself! If it rounded down, gets could return an empty  
string, and code like:

	while s = f.gets(1) .....

would then go into an infinite loop.

Mike.