[rrd-developers] Re: BUG: attempt to put segment in horiz list twice ??

[Per Jessen]

Ruud H.G. van Tol wrote:

> OK, but then I don't understand how the stderr-data could get mixed with
> the PNG-data. Or did I understand that wrong?
> Does libart maybe send error messages to stdout too? 

when I use "rrdtool graph -", everything that is sent to stdout and stderr ends up on
stdout, and therefore ends up being part of the PNG (when I pipe it direct to a browser). 
Before I call system(), I redirect stdout to my http pipe.  Afterwards, when I tried to
divert stderr away (to make the PNG "clean"), the browser hangs as if the PNG hasn't
completely transferred.  

The code that occasionally produces bad PNGs: 

        oldstdout=dup(1);       // take a copy of stdout
        dup2(s,1);              // make stdout = s  (client http socket)

        system(buffer);         // call rrdtool to do the biz.

        dup2(oldstdout,1);      // restore stdout.

The code that produces good PNGs but make the browser hang:

        oldstdout=dup(1);       // take a copy of stdout
        oldstderr=dup(2);
        dup2(s,1);              // make stdout = s
        close(2);               // close stderr

        system(buffer);         // call rrdtool to do the biz.

        dup2(oldstdout,1);      // restore stdout.
        dup2(oldstderr,2);


> In a system() call, you can append " 2>$tmpfile" to the commandline.

Yeah, I did think of that too - I'll have to try it again, but I think it produced the
same result (browser hangs).


/Per Jessen, Zürich

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