Re: Advice on streams and bsd sockets

On 2014-01-21, Michael Jones <[email protected]> wrote:
> I am looking for some advice on using streams with sockets. I am using CYGPKG_NET and taking the socket handle and creating a stream with fdopen(). 
>
> A fwrite() eventually arrives in this code:
>
> static int 
> bsd_lseek(struct CYG_FILE_TAG *fp, off_t *pos, int whence)
> {
>     return ESPIPE;
> }
>
> And this causes an error, but a second call to fwrite() works. It
> always happens when there is a fwrite() immediately after a fread(),
> as that triggers the seek.
>
> I am looking for advice on how to handle this problem.

What I would do is first add a diag_printf() to bsd_lseek() to print
out the paramters so you can see exactly what sort of seek is being
attempted.  You could add a bit of code to bsd_lseek() to check for
(and return success for) "noop" operations (e.g. seek to 0 offset from
current location).

> Of course I could not use streams, but I am working with lua 5.2.3
> and it is based on streams, and don't want to modify it that much. I
> also can't turn off buffering, because lua relies on the ability to
> push bytes back into the stream after reading them.
>
> Does anyone have a patch that works around the problem or know of
> some other way to create a stream that does not rely on seek? In the
> case where I use it, there is no need for seek anyway. I am using the
> stream in place of stdin and stdout so that lua can interact with a
> telnet session.

If the code works OK with stdin/stdout streams, then the lseek() calls
must not be actually doing anything, right?  If that's the case, then
it should be easy enough to modify the the bsd_lseek() function to do
the same.

-- 
Grant Edwards               grant.b.edwards        Yow! I haven't been married
                                  at               in over six years, but we
                              gmail.com            had sexual counseling every
                                                   day from Oral Roberts!!


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