Thumbnailing

Creating document thumbnails

Performed by the coils.blob.autothumb component which creates a set of workers to perform thumbnailing of documents

Possible Issues

• does this correctly serialize multiple updates to a document? we should try to squeeze out rapid fire events.

Document Types

PDF

The PDF thumbnailer uses the convert utility provided by ImageMagick to make and image of the first page of the document

signal.signal(signal.SIGALRM, timeout_alarm_handler)
signal.alarm(CONVERSION_TIMEOUT_SECONDS)

# convert -format pdf -[0] -thumbnail 175x -bordercolor white png:-

converter = Popen(
    [
        '/usr/bin/convert', '-format', 'pdf', '-[0]',
        '-thumbnail', '175x', '-bordercolor', 'white', 'png:-',
    ],
    stdin=PIPE,
    stdout=sfile,
)
(converter_in, converter_out, ) = (
    converter.stdin, converter.stdout,
)

shutil.copyfileobj(rfile, converter_in)
converter_in.close()
converter.communicate()
signal.alarm(0)

The problem, as always, with using external executables is untraceable dependencies - think fonts - as well as error management. Did it work? If not why not. Is the executable even there? Is it a good version?

Note: we expect the OS to provide a sane installation of convert.

[root@coils-red ~]# rpm -qf /usr/bin/convert
ImageMagick-6.5.4.7-7.el6_5.x86_64

What does convert look like when an input document is not a PDF?

awilliam@linux-86wr:~> cat test.pdf | convert -format pdf -[0] \
    -thumbnail 175x -bordercolor white png:file.png
convert: no decode delegate for this image format `/tmp/magick-3499W14ZgJKucF6t' @ error/svg.c/ReadSVGImage/2954.
convert: no images defined `png:file.png' @ error/convert.c/ConvertImageCommand/3187.
awilliam@linux-86wr:~> echo $?
1
awilliam@linux-86wr:~> ls -l file.png
ls: cannot access file.png: No such file or directory

__Coils Log___

2015-06-05T14:55:39:context:DEBUG: duration of document::get-handle was 0.081
2015-06-05T14:55:39:context:DEBUG: converter completed with exit code 1 for OGo#314232599 [Document]
2015-06-05T14:55:39:context:INFO: recording 165b of stderr content from convert for OGo#314232599 [Document] to audit log
2015-06-05T14:55:39:context:INFO: stderr content queued for commit

What does convert look like when it fails to process a PDF?

???

What does convert look like when it works?

awilliam@linux-86wr:~> cat Downloads/03-december-2014ridershipproductivityreport.pdf \
  | convert -format pdf -[0] -thumbnail 175x -bordercolor white png:file.png
awilliam@linux-86wr:~> echo $?
0
awilliam@linux-86wr:~> ls -l file.png
-rw-r--r-- 1 awilliam users 27715 May  6 08:41 file.png