extending tags in "a"ppend mode?

[Juergen Buchmueller]

Hi list,

should it be possible to extend the tags of (the first directory of) an
existing tiff file opened in "a"ppend mode?

What I'm trying to do is:
+ open an existing tiff file with TIFFOpen(...,"a")
+ create an array of TIFFFieldInfo
+ call TIFFMergeFieldInfo() with this array and count
+ Write some (string) tags that were defined in the array
+ close the tiff handle with TIFFClose()

It seems that TIFFClose() hangs somewhere and doesn't return, which is
why I suspect that what I'm trying to do is impossible.

Juergen
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[Frank Warmerdam-2]

Juergen Buchmueller wrote:

> Hi list,
>
> should it be possible to extend the tags of (the first directory of) an
> existing tiff file opened in "a"ppend mode?
>
> What I'm trying to do is:
> + open an existing tiff file with TIFFOpen(...,"a")
> + create an array of TIFFFieldInfo
> + call TIFFMergeFieldInfo() with this array and count
> + Write some (string) tags that were defined in the array
> + close the tiff handle with TIFFClose()
>
> It seems that TIFFClose() hangs somewhere and doesn't return, which is
> why I suspect that what I'm trying to do is impossible.

Juergen,

It should be possible to extend the first directory with new tags by opening
in "r+" (update) mode, setting the tags and closing.  I don't know why you are
seeing the behavior you encountered.  I would have expected it to attempt to
append a new image directory and complain about your not providing a complete
set of tags to define an image.

It might be helpful if you provided a minimal program and file demonstrating
your problem.

Also, in place update of directories is always an iffy procedure with libtiff
but I would strongly encourage using the most recent release (3.9.1?) if you
are trying this.

Best regards,
--
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam@...
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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[Juergen Buchmueller]

On Wed, 28 Oct 2009 12:02:09 -0400
Frank Warmerdam <warmerdam@...> wrote:

> Juergen,
>
> It should be possible to extend the first directory with new tags by opening
> in "r+" (update) mode, setting the tags and closing.  I don't know why you are
> seeing the behavior you encountered.  I would have expected it to attempt to
> append a new image directory and complain about your not providing a complete
> set of tags to define an image.

Ok, I didn't know that "r+" was supported because it isn't mentioned in
the docs.

> It might be helpful if you provided a minimal program and file demonstrating
> your problem.

See attachment. This crashes when I try to run it on the file:
        http://pmbits.ath.cx/RECV002.TIF

Compiled with (adapt include + lib paths):
        gcc -I/usr/pkg/include -Wl,-R/usr/pkg/lib \
                -L/usr/pkg/lib -ltiff -o addtags addtags.c

Run with:
        ./addtags somewhere/RECV002.TIF

Stack backtrace:
Program terminated with signal 11, Segmentation fault.
#0  0x00007f7ffd98eb6a in _malloc_prefork () from /usr/lib/libc.so.12
(gdb) bt
#0  0x00007f7ffd98eb6a in _malloc_prefork () from /usr/lib/libc.so.12
#1  0x00007f7ffd98edde in free () from /usr/lib/libc.so.12
#2  0x00007f7ffdc08959 in TIFFCleanup () from /usr/pkg/lib/libtiff.so.3
#3  0x00007f7ffdc089e1 in TIFFClose () from /usr/pkg/lib/libtiff.so.3
#4  0x0000000000400dbe in main ()

To me it looks like a double free() of some kind!?

> Also, in place update of directories is always an iffy procedure with libtiff
> but I would strongly encourage using the most recent release (3.9.1?) if you
> are trying this.

Yes, on my system (NetBSD-5.0.1) there is libtiff-3.9.1 installed.

Thanks,
Juergen

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <tiffio.h>

static const char *some_strings[] = {
        "Hello, world!",
        "foo",
        "bar",
        "baz"
};


int main(int argc, char **argv)
{
        TIFF *hTIFF;
        TIFFFieldInfo *apptags;
        char buff[32];
        const char *str;
        uint32_t n, ntags;
        int32_t res;

        hTIFF = TIFFOpen(argv[1], "r+");

        ntags = 3;
        apptags = calloc(ntags, sizeof(TIFFFieldInfo));
        for (n = 0; n < ntags; n++) {
                uint16_t id = 10000 + n;
                apptags[n].field_tag = id;
                apptags[n].field_readcount = TIFF_VARIABLE;
                apptags[n].field_writecount = TIFF_VARIABLE;
                apptags[n].field_type = TIFF_ASCII;
                apptags[n].field_bit = FIELD_CUSTOM;
                apptags[n].field_oktochange = 1;
                apptags[n].field_passcount = 0;
                snprintf(buff, sizeof(buff), "Tag %d", id);
                apptags[n].field_name = strdup(buff);
        }
        TIFFMergeFieldInfo(hTIFF, apptags, ntags);

        for (n = 0; n < ntags; n++) {
                str = some_strings[n];
                res = TIFFSetField(hTIFF, apptags[n].field_tag, str);
                printf("set tag:%u to \"%s\" res:%d\n",
                        apptags[n].field_tag, str, res);
        }

        TIFFClose(hTIFF);

        for (n = 0; n < ntags; n++) {
                if (apptags[n].field_name)
                        free(apptags[n].field_name);
        }
        free(apptags);

        return 0;
}

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[Juergen Buchmueller]

On Wed, 28 Oct 2009 17:28:34 +0100
Juergen Buchmueller <pullmoll@...> wrote:

> See attachment. This crashes when I try to run it on the file:

Funny enough the crash goes away if I choose a different name for my own
tags. Perhaps a collision or lazy assumption with the autogenerated
names (which would be the same)?

-                snprintf(buff, sizeof(buff), "Tag %d", id);
+                snprintf(buff, sizeof(buff), "test%d", id);

Now the test program runs without error message, yet the TIFF file
doesn't contain the new tags. Hmm...

Juergen
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[Juergen Buchmueller]

Ok, the problem seems to be solved now.

I need to choose tag names different from the ones that libtiff would
use on the auto-registration when reading a file, and I need to call
TIFFWriteDirectory() after writing the tags and before closing the file
again.

Perhaps this little episode helps others in similiar situations.

Cheers,
Juergen
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