Re: [hylafax-devel] ImageLength missing in recvq TIFF files for interrupted transmission

[<pa...@ur...>]

Makes sense. Many thanks Lee!

 

--

Pawel

 

From: Lee Howard <fa...@ho...> 
Sent: Thursday, February 11, 2021 11:53 PM
To: pa...@ur...; hyl...@li...
Subject: Re: [hylafax-devel] ImageLength missing in recvq TIFF files for
interrupted transmission

 

When HylaFAX answers a call it creates a TIFF file and starts a TIFF
directory (page).  No data is in it yet.  It then starts to write data into
the directory as it gets it, and at the end of the communication it write
the number of received lines into the directory.

If the communication is interrupted after a page is started but before any
data is received, then HylaFAX has an empty directory in the TIFF file that
it can't easily dispose of without rewriting the TIFF file.  This is the
condition of your fax000000944.tif file.

The proper thing for the TIFF application to do with such a TIFF file is to
process the directories that have data and skip or ignore pages that don't.
Applications may issue warnings or error messages, but they shouldn't fail
to process the directories that have data.  Unfortunately, tiff2pdf doesn't
process the data that it could.  This is a problem with tiff2pdf, and you
may get some traction by filing a bug report with them.

However, it may just be easier to pre-process the TIFF file before handing
it off to tiff2pdf or whatever other application you may be using:

tiffcp -i fax000000944.tif fax000000944-new.tif

... then work with the "new" file.  This will solve a lot of ills related to
this condition as well as other tricky situations (like a non-ECM fax
receiving corrupt MH/MR data from the sender).  This can be done within the
faxrcvd, FaxAccounting, or FaxDispatch scripts as may suit your situation
best.

One might say that HylaFAX should only produce perfectly clean TIFF files as
output.  I can understand that perspective... I certainly sympathize with it
(as I have to use the same tiffcp for all of the faxes that I receive).
However, historically HylaFAX was designed to have the TIFF file honestly
reflect the fax communication as best as possible... so by default data
isn't being altered in the TIFF file from what was sent by the sender.  This
may or may not make practical sense, but it's the design that HylaFAX has
had since the beginning.  In some forensic or diagnostic sense the "raw"
state of the TIFF files is sometimes helpful, though.

Thanks,

Lee.


On 02/10/2021 02:28 PM, pa...@ur... <mailto:pa...@ur...>
wrote:

Hello,

When the inbound fax transmission is interrupted, the tiff file generated in
the recvq directory is missing the ImageLength field.

Some apps using libtiff have issues with these files. For example, tiff2pdf:

[root@hylafax tmp]# tiff2pdf -p A4  -o 944.pdf fax000000944.tif

MissingRequired: TIFF directory is missing required "ImageLength" field.

tiff2pdf: Can't set directory 3 of input file fax000000944.tif.

tiff2pdf: An error occurred creating output PDF file

 

Example tiff file (zipped) - 3 pages, the last one was interrupted:

https://drive.google.com/file/d/16edQY9NZkq5mNNALqEyx6TARefwa3GlH/view?usp=s
haring

 

Hylafax+ 7.0.3

CentOS 7(2009)

 

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Pawel