"The document 'xxx' could not be opened" in listener mode

[PierreSchwang]

Possibly relates to #237 #483 #402 - Root cause found in gotenberg/gotenberg#516 (issue is in unoconv)

Goal

Converting plain PDF-files to PDF/A-1a files

Commands

unoconv --no-launch --format pdf --port 45379 -vvv --export SelectPdfVersion=1 --output out.pdf xxx.pdf

Problem Description

Using the listener-mode the PDF conversion will work at first, but fails after the libreoffice listener hasn't received any jobs in a bit (e.g. 20 minutes). In that case, the following output will happen (exit code 5):

Verbosity set to level 3
Using office base path: /usr/lib/libreoffice
Using office binary path: /usr/lib/libreoffice/program
DEBUG: Connection type: socket,host=127.0.0.1,port=45379,tcpNoDelay=1;urp;StarOffice.ComponentContext
Input file: xxxx.pdf
unoconv: UnoException during import phase:
The document 'file:///home/gotenberg/xxxx.pdf' could not be opened.

Sadly I haven't found any logs regarding LibreOffice anywhere.
When killing the libreoffice process, which will force a recreation of libreoffice by unoconv, that'll be fixed. That's just no option for a production usage.

Expectation

The libreoffice listener should accept commands even after having no jobs for a few hours or more. The instance itself seems to be healthy, no error is thrown in https://github.com/unoconv/unoconv/blob/master/unoconv#L1015 which makes the debugging not really possible.

Are there any alternatives?

Sadly, https://github.com/unoconv/unoserver/ is no alternative in this case as unoserver does not support the PDF/A conversion (yet?)