add backup of datastore.php when adding new link

[landure]

For an unknown reason, my datastore.php file was emptied after successfully adding a new link.

To prevent this, please add an automatic backup of the datastore previous version, with automatic restoration in case of corrupted datastore.

[nodiscc]

Hi @landure, we need to know what led to this situation in the first place. There used to be a data corruption bug when the disk was full and an attempt to write the datastore was made, but it was fixed a long while ago: #1810

Which shaarli version are you running? Which installation method? Was the disk full at some point (the disk space check should have caught that)? Any error or unusual messages in server logs?

An automatic backup copy of the datastore of the datastore file could make sense, but this kind of corruption should not happen in the first place.

[landure]

Hi, i don't know the reason. I was with v0.14.0 hosted on Docker. I don't think my disk was full, but I can't say it wasn't the case. I've no idea what occurred, but having a move command before writing the new file version would prevent data loss issues.

[landure]

Ok, i think i've identified the reason for the empty datastore. My shaarli container was limited to 256m available memory, witch cause php-fpm process to be killed due to OOM in the container. This is probably what caused the datastore.php empty contents.

The issue stays that in case of catastrophic failure during writing, shaarli looses all data.

[nodiscc]

We could probably make the operation more atomic by first writing to datastore.tmp.php then moving this file to datastore.php

[landure]

I've just had the issue again, It's triggered by editing the last added link. My datastore file has contents. It's linked to this comment.

datastore.php.gz

I've found no outstanding error in docker container logs.

An unexpected error happened, and the error template could not be displayed.

unserialize(): Argument #1 ($data) must be of type string, bool given
/var/www/shaarli/application/bookmark/BookmarkIO.php92
#0 /var/www/shaarli/application/bookmark/BookmarkIO.php(92): unserialize()

To reproduce:

• add https://github.com/antonbabenko/pre-commit-terraform to shaarli
• the link is added successfully.
• visit the shaarli site, the link is displayed on first page.
• click the button to edit the link. It displays the error, not the edition form. Following this, the datastore is corrupted.