Re: read buffer length problem in grep on windows

[Alain Magloire]

> 
> Hi-
>       I tracked down (and then discovered others had as well after doing a
> quick google search) a bug in the Microsoft console code which renders grep
> unable to read from stdin. I tested 2.5, but also read the current CVS
> source code and the problem still appears to exist there as well.
>       I'm pretty sure that the fix is trivial, though I'm not familiar
> enough with the code to be sure there are no side effects:
> if line 216 of grep.c is changed from:
>       #define INITIAL_BUFSIZE 32768   /* Initial buffer size, not counting
> slop. */
> to something like
>       #if defined (_WIN32)
>       # define INITIAL_BUFSIZE 16384  /* Initial buffer size, not counting
> slop. */      
>       #else
>       # define INITIAL_BUFSIZE 32768  /* Initial buffer size, not counting
> slop. */
>       #endif
> Then it avoids the Microsoft bug. I'm not sure if it's better to use the
> actual limit (30704) or to use a power of 2 (hence the 16384).
> 
> Without this fix, the command "grep PATTERN" results in:
>       grep: (standard input): Not enough space
> With the fix, it properly reads from stdin.
> 
> The following C program demonstrates the Microsoft bug:
> 
> #include <stdio.h>
> 
> int main()
> {
>     int n;
>     char good_buf[30704] = {0};
>     char bad_buf[30705] = {0};
> 
>     /* due to a bug in the Microsoft console, the following will fail, and
>        print -1 w/o reading any input */
>     n =       read (0, bad_buf, sizeof(bad_buf));
>     printf( "%d %s\n", n, bad_buf);
> 
>     /* this read request is small enough, so stdin will be read, then echoed
> */
>     n =       read (0, good_buf, sizeof(good_buf));
>     printf( "%d %s\n", n, good_buf);
> 
> }
> 
> Sorry in advance to CC each of the developers on this, but it wasn't clear
> to me who the best person to contact was. If there is a better person to
> submit this fix to, please let me know.
> 
> Also, if you're interested, I managed to build a working grep for windows
> w/o cygwin tools, but had to make two additions to the source package:
> dirent.c (which implements opendir and friends using the windows API) and
> getpagesize.c (which implements getpagesize). I also manually created a
> config.h that works for both the Microsoft and GHS compilers. If anyone's
> interested, I'm happy to provide the code (it's only a few dozen lines).
> 

Contacting the grep maintainer would be the best thing.
This particular code was implemented by Paul, IIRC.

I'm no longer familiar with the code to be of any help.