Corrupted preview *-max.png blocks generation of other previews

[streckus]

Steps to reproduce

1. Upload around 100 pictures in a folder
2. Visit folder in files or gallery app
3. If resources are limited preview generation for some files might crash, resulting in a corrupted *-max.png file.

Expected behaviour

When visiting the folder again and that broken preview is detected (e.g. Gallery app throws "Exception: Preview generation has failed"), the broken file should be regenerated to not block generation of other previews.

Actual behaviour

The software seems to assume the only cause for the broken preview can be a broken file in the first place, so the broken preview file blocks further preview generation. Manually removing the corrupted preview file and running occ files:scan-app-data to update the cache enables new preview generation at next folder visit.

Server configuration

Operating system: Arch Linux ARM (on Raspberry Pi 3)

Web server: Apache 2.4.29

Database: MariaDB 10.1.30

PHP version: 7.0.26

Nextcloud version: 12.0.4

Updated from an older Nextcloud/ownCloud or fresh install: fresh install

Where did you install Nextcloud from: Arch Repositories

Signing status:

Signing status

No errors have been found.

List of activated apps:

App list

Enabled:
  - activity: 2.5.2
  - comments: 1.2.0
  - dav: 1.3.0
  - federatedfilesharing: 1.2.0
  - federation: 1.2.0
  - files: 1.7.2
  - files_pdfviewer: 1.1.1
  - files_sharing: 1.4.0
  - files_texteditor: 2.4.1
  - files_trashbin: 1.2.0
  - files_versions: 1.5.0
  - files_videoplayer: 1.1.0
  - firstrunwizard: 2.1
  - gallery: 17.0.0
  - logreader: 2.0.0
  - lookup_server_connector: 1.0.0
  - music: 0.5.5
  - nextcloud_announcements: 1.1
  - notifications: 2.0.0
  - oauth2: 1.0.5
  - password_policy: 1.2.2
  - provisioning_api: 1.2.0
  - serverinfo: 1.2.0
  - sharebymail: 1.2.0
  - survey_client: 1.0.0
  - systemtags: 1.2.0
  - theming: 1.3.0
  - twofactor_backupcodes: 1.1.1
  - updatenotification: 1.2.0
  - workflowengine: 1.2.0
Disabled:
  - admin_audit
  - encryption
  - files_external
  - user_external
  - user_ldap

Nextcloud configuration:

Config report

{
    "system": {
        "instanceid": "ocmuug5kqo74",
        "apps_paths": [
            {
                "path": "\/usr\/share\/webapps\/nextcloud\/apps",
                "url": "\/apps",
                "writable": false
            },
            {
                "path": "\/mnt\/nextcloud_data\/nextcloud\/apps2",
                "url": "\/apps2",
                "writable": true
            }
        ],
        "datadirectory": "\/mnt\/nextcloud_data\/nextcloud\/data",
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "streckemich.ddns.net"
        ],
        "overwrite.cli.url": "https:\/\/streckemich.ddns.net",
        "dbtype": "mysql",
        "version": "12.0.4.3",
        "dbname": "nextcloud",
        "dbhost": "localhost",
        "dbport": "",
        "dbtableprefix": "oc_",
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "installed": true,
        "memcache.local": "\\OC\\Memcache\\APCu",
        "mail_smtpmode": "sendmail",
        "mail_smtpauthtype": "LOGIN",
        "mail_smtpauth": 1,
        "mail_smtphost": "securesmtp.t-online.de",
        "mail_smtpport": "465",
        "mail_smtpname": "***REMOVED SENSITIVE VALUE***",
        "mail_smtppassword": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpsecure": "ssl",
        "mail_from_address": "nextcloud",
        "mail_domain": "streckemich.ddns.net",
        "enable_previews": true,
        "enabledPreviewProviders": [
            "OC\\Preview\\PNG",
            "OC\\Preview\\JPEG",
            "OC\\Preview\\GIF",
            "OC\\Preview\\BMP",
            "OC\\Preview\\XBitmap",
            "OC\\Preview\\MP3",
            "OC\\Preview\\TXT",
            "OC\\Preview\\MarkDown",
            "OC\\Preview\\Movie",
            "OC\\Preview\\PDF"
        ],
        "maintenance": false,
        "log_level": 0
    },
    "apps": {
        "activity": {
            "enabled": "yes",
            "installed_version": "2.5.2",
            "types": "filesystem"
        },
        "backgroundjob": {
            "lastjob": "823"
        },
        "bruteforcesettings": {
            "enabled": "no",
            "installed_version": "1.0.3",
            "types": ""
        },
        "comments": {
            "enabled": "yes",
            "installed_version": "1.2.0",
            "types": "logging"
        },
        "core": {
            "installed.bundles": "[\"CoreBundle\"]",
            "installedat": "1514663107.139",
            "lastcron": "1515452039",
            "lastupdateResult": "[]",
            "lastupdatedat": "1515451325",
            "oc.integritycheck.checker": "[]",
            "public_files": "files_sharing\/public.php",
            "public_webdav": "dav\/appinfo\/v1\/publicwebdav.php",
            "scss.variables": "1f5da376b00eb86a92030ba656c8f86c",
            "vendor": "nextcloud"
        },
        "dav": {
            "enabled": "yes",
            "installed_version": "1.3.0",
            "types": "filesystem"
        },
        "federatedfilesharing": {
            "enabled": "yes",
            "installed_version": "1.2.0",
            "types": ""
        },
        "federation": {
            "enabled": "yes",
            "installed_version": "1.2.0",
            "types": "authentication"
        },
        "files": {
            "cronjob_scan_files": "500",
            "enabled": "yes",
            "installed_version": "1.7.2",
            "types": "filesystem"
        },
        "files_pdfviewer": {
            "enabled": "yes",
            "installed_version": "1.1.1",
            "ocsid": "166049",
            "types": ""
        },
        "files_sharing": {
            "enabled": "yes",
            "installed_version": "1.4.0",
            "types": "filesystem"
        },
        "files_texteditor": {
            "enabled": "yes",
            "installed_version": "2.4.1",
            "ocsid": "166051",
            "types": ""
        },
        "files_trashbin": {
            "enabled": "yes",
            "installed_version": "1.2.0",
            "types": "filesystem"
        },
        "files_versions": {
            "enabled": "yes",
            "installed_version": "1.5.0",
            "types": "filesystem"
        },
        "files_videoplayer": {
            "enabled": "yes",
            "installed_version": "1.1.0",
            "types": ""
        },
        "firstrunwizard": {
            "enabled": "yes",
            "installed_version": "2.1",
            "types": "logging"
        },
        "folderplayer": {
            "enabled": "no",
            "installed_version": "10.0.0",
            "types": ""
        },
        "gallery": {
            "enabled": "yes",
            "installed_version": "17.0.0",
            "types": ""
        },
        "logreader": {
            "enabled": "yes",
            "installed_version": "2.0.0",
            "ocsid": "170871",
            "types": ""
        },
        "lookup_server_connector": {
            "enabled": "yes",
            "installed_version": "1.0.0",
            "types": "authentication"
        },
        "music": {
            "enabled": "yes",
            "installed_version": "0.5.5",
            "types": "filesystem"
        },
        "nextcloud_announcements": {
            "enabled": "yes",
            "installed_version": "1.1",
            "pub_date": "Sat, 10 Dec 2016 00:00:00 +0100",
            "types": "logging"
        },
        "notifications": {
            "enabled": "yes",
            "installed_version": "2.0.0",
            "types": "logging"
        },
        "oauth2": {
            "enabled": "yes",
            "installed_version": "1.0.5",
            "types": "authentication"
        },
        "password_policy": {
            "enabled": "yes",
            "installed_version": "1.2.2",
            "types": ""
        },
        "previewgenerator": {
            "enabled": "no",
            "heightSizes": "256",
            "installed_version": "1.0.9",
            "squareSizes": "32",
            "types": "filesystem",
            "widthSizes": "256"
        },
        "provisioning_api": {
            "enabled": "yes",
            "installed_version": "1.2.0",
            "types": "prevent_group_restriction"
        },
        "radio": {
            "enabled": "no",
            "installed_version": "0.6.0",
            "types": ""
        },
        "serverinfo": {
            "enabled": "yes",
            "installed_version": "1.2.0",
            "types": ""
        },
        "sharebymail": {
            "enabled": "yes",
            "installed_version": "1.2.0",
            "types": "filesystem"
        },
        "survey_client": {
            "enabled": "yes",
            "installed_version": "1.0.0",
            "types": ""
        },
        "systemtags": {
            "enabled": "yes",
            "installed_version": "1.2.0",
            "types": "logging"
        },
        "theming": {
            "cachebuster": "2",
            "enabled": "yes",
            "installed_version": "1.3.0",
            "types": "logging"
        },
        "twofactor_backupcodes": {
            "enabled": "yes",
            "installed_version": "1.1.1",
            "types": ""
        },
        "updatenotification": {
            "enabled": "yes",
            "installed_version": "1.2.0",
            "types": "",
            "update_check_errors": "0"
        },
        "workflowengine": {
            "enabled": "yes",
            "installed_version": "1.2.0",
            "types": "filesystem"
        }
    }
}

Are you using external storage, if yes which one: no

Are you using encryption: no

Are you using an external user-backend, if yes which one: no

Client configuration

Browser: Opera (Also tested on Firefox)

Operating system: Arch Linux, Windows 10, Linux Mint 17.3

Logs

Nextcloud log (data/nextcloud.log)

Nextcloud log

{"reqId":"AxdzGrAhccjYzDD3OWH2","level":3,"time":"2018-01-08T20:41:18+00:00","remoteAddr":"192.168.2.114","user":"NextAdmin","app":"gallery","method":"GET","url":"\/index.php\/apps\/gallery\/thumbnails?ids=16859%3B16858%3B16860%3B16861%3B16864%3B16863&scale=1&square=0&requesttoken=CKVhdQsuNWUWsbnz9xfVO8THE3LxiAqz2uka3Bd%2BI3Y%3D%3AacJUBTlDclBH%2FPiip2W2DoyWJEbF%2BEaD7p8vjEJGYRk%3D","message":"Exception: Preview generation has failed","userAgent":"Mozilla\/5.0 (X11; Linux x86_64) AppleWebKit\/537.36 (KHTML, like Gecko) Chrome\/63.0.3239.108 Safari\/537.36 OPR\/50.0.2762.45","version":"12.0.4.3"}
{"reqId":"kvT8wGniKAZx1EE62Mw8","level":3,"time":"2018-01-08T20:41:19+00:00","remoteAddr":"192.168.2.114","user":"NextAdmin","app":"gallery","method":"GET","url":"\/index.php\/apps\/gallery\/thumbnails?ids=16866%3B16867%3B16870%3B16872%3B16874%3B16875&scale=1&square=0&requesttoken=CKVhdQsuNWUWsbnz9xfVO8THE3LxiAqz2uka3Bd%2BI3Y%3D%3AacJUBTlDclBH%2FPiip2W2DoyWJEbF%2BEaD7p8vjEJGYRk%3D","message":"Exception: Preview generation has failed","userAgent":"Mozilla\/5.0 (X11; Linux x86_64) AppleWebKit\/537.36 (KHTML, like Gecko) Chrome\/63.0.3239.108 Safari\/537.36 OPR\/50.0.2762.45","version":"12.0.4.3"}
{"reqId":"ettJH94uoCs3ffS2rRjh","level":3,"time":"2018-01-08T20:42:03+00:00","remoteAddr":"192.168.2.114","user":"NextAdmin","app":"gallery","method":"GET","url":"\/index.php\/apps\/gallery\/thumbnails?ids=16859%3B16858%3B16860%3B16861%3B16864%3B16863&scale=1&square=0&requesttoken=DBC0o0npm8JVwTl4mwq%2Fg0Fd76TAhqBveBQpVDDDAg8%3D%3AbXeB03uE3PcEjHgpy3jctgkM2JD09uxfTGIcBGX7QGA%3D","message":"Exception: Preview generation has failed","userAgent":"Mozilla\/5.0 (X11; Linux x86_64) AppleWebKit\/537.36 (KHTML, like Gecko) Chrome\/63.0.3239.108 Safari\/537.36 OPR\/50.0.2762.45","version":"12.0.4.3"}
{"reqId":"o8SDlmDBrAcUxrw2r2tC","level":3,"time":"2018-01-08T20:42:03+00:00","remoteAddr":"192.168.2.114","user":"NextAdmin","app":"gallery","method":"GET","url":"\/index.php\/apps\/gallery\/thumbnails?ids=16866%3B16867%3B16870%3B16872%3B16874%3B16875&scale=1&square=0&requesttoken=DBC0o0npm8JVwTl4mwq%2Fg0Fd76TAhqBveBQpVDDDAg8%3D%3AbXeB03uE3PcEjHgpy3jctgkM2JD09uxfTGIcBGX7QGA%3D","message":"Exception: Preview generation has failed","userAgent":"Mozilla\/5.0 (X11; Linux x86_64) AppleWebKit\/537.36 (KHTML, like Gecko) Chrome\/63.0.3239.108 Safari\/537.36 OPR\/50.0.2762.45","version":"12.0.4.3"}
{"reqId":"UY6IzkWYSC7BaRmDYzMZ","level":3,"time":"2018-01-08T20:43:38+00:00","remoteAddr":"192.168.2.114","user":"NextAdmin","app":"gallery","method":"GET","url":"\/index.php\/apps\/gallery\/thumbnails?ids=16859%3B16858%3B16860%3B16861%3B16864%3B16863&scale=1&square=0&requesttoken=gp9ott4iV%2B9As0c93ot9At0srOKMBylQpxlt0DOg4fo%3D%3A1vkN5LpzH71wyzZVvKAbb%2FZ%2Bh6DlVXAS401YklLV0rU%3D","message":"Exception: Preview generation has failed","userAgent":"Mozilla\/5.0 (X11; Linux x86_64) AppleWebKit\/537.36 (KHTML, like Gecko) Chrome\/63.0.3239.108 Safari\/537.36 OPR\/50.0.2762.45","version":"12.0.4.3"}
{"reqId":"v7kSysF0ObdMgBTSrJ65","level":3,"time":"2018-01-08T20:43:38+00:00","remoteAddr":"192.168.2.114","user":"NextAdmin","app":"gallery","method":"GET","url":"\/index.php\/apps\/gallery\/thumbnails?ids=16866%3B16867%3B16870%3B16872%3B16874%3B16875&scale=1&square=0&requesttoken=gp9ott4iV%2B9As0c93ot9At0srOKMBylQpxlt0DOg4fo%3D%3A1vkN5LpzH71wyzZVvKAbb%2FZ%2Bh6DlVXAS401YklLV0rU%3D","message":"Exception: Preview generation has failed","userAgent":"Mozilla\/5.0 (X11; Linux x86_64) AppleWebKit\/537.36 (KHTML, like Gecko) Chrome\/63.0.3239.108 Safari\/537.36 OPR\/50.0.2762.45","version":"12.0.4.3"}
{"reqId":"MbX1LSJRhOHYN3Nqned9","level":3,"time":"2018-01-08T20:47:08+00:00","remoteAddr":"192.168.2.114","user":"NextAdmin","app":"gallery","method":"GET","url":"\/index.php\/apps\/gallery\/thumbnails?ids=16859%3B16858%3B16860%3B16861%3B16864%3B16863&scale=1&square=0&requesttoken=xtjCcdmxL6cqRjV1w32KULF5P4IQYP245nNyohSZJHk%3D%3Akr6nI73gZ%2FUaPkQdoVbsPZorFMB5MqT6oidH4HXsFzY%3D","message":"Exception: Preview generation has failed","userAgent":"Mozilla\/5.0 (X11; Linux x86_64) AppleWebKit\/537.36 (KHTML, like Gecko) Chrome\/63.0.3239.108 Safari\/537.36 OPR\/50.0.2762.45","version":"12.0.4.3"}
{"reqId":"JfxT1eWBIhcSgzmq7BQg","level":3,"time":"2018-01-08T20:47:08+00:00","remoteAddr":"192.168.2.114","user":"NextAdmin","app":"gallery","method":"GET","url":"\/index.php\/apps\/gallery\/thumbnails?ids=16866%3B16867%3B16870%3B16872%3B16874%3B16875&scale=1&square=0&requesttoken=xtjCcdmxL6cqRjV1w32KULF5P4IQYP245nNyohSZJHk%3D%3Akr6nI73gZ%2FUaPkQdoVbsPZorFMB5MqT6oidH4HXsFzY%3D","message":"Exception: Preview generation has failed","userAgent":"Mozilla\/5.0 (X11; Linux x86_64) AppleWebKit\/537.36 (KHTML, like Gecko) Chrome\/63.0.3239.108 Safari\/537.36 OPR\/50.0.2762.45","version":"12.0.4.3"}
{"reqId":"UxhIIwxDN4Vsb6UWV9KI","level":3,"time":"2018-01-08T21:21:12+00:00","remoteAddr":"192.168.2.114","user":"NextAdmin","app":"gallery","method":"GET","url":"\/index.php\/apps\/gallery\/thumbnails?ids=16859%3B16858%3B16860%3B16861%3B16864%3B16863&scale=1&square=0&requesttoken=8t1lSzLcR9ZVSDfRuZA6uVwB4Sk%2F56CbqQv4u%2BKB3ms%3D%3AprsAGVaND4RlMEa527tc1HdTymtWtfnZ7V%2FN%2BYP07SQ%3D","message":"Exception: Preview generation has failed","userAgent":"Mozilla\/5.0 (X11; Linux x86_64) AppleWebKit\/537.36 (KHTML, like Gecko) Chrome\/63.0.3239.108 Safari\/537.36 OPR\/50.0.2762.45","version":"12.0.4.3"}
{"reqId":"8PKZ97iqdYFnqHbhtFGK","level":3,"time":"2018-01-08T21:21:13+00:00","remoteAddr":"192.168.2.114","user":"NextAdmin","app":"gallery","method":"GET","url":"\/index.php\/apps\/gallery\/thumbnails?ids=16866%3B16867%3B16870%3B16872%3B16874%3B16875&scale=1&square=0&requesttoken=8t1lSzLcR9ZVSDfRuZA6uVwB4Sk%2F56CbqQv4u%2BKB3ms%3D%3AprsAGVaND4RlMEa527tc1HdTymtWtfnZ7V%2FN%2BYP07SQ%3D","message":"Exception: Preview generation has failed","userAgent":"Mozilla\/5.0 (X11; Linux x86_64) AppleWebKit\/537.36 (KHTML, like Gecko) Chrome\/63.0.3239.108 Safari\/537.36 OPR\/50.0.2762.45","version":"12.0.4.3"}

[MorrisJobke]

cc @rullzer

[rullzer]

mmmm yes that makes sense. Because all the previews are generated from the max preview...

@streckus is the size of your max always zero?

[streckus]

@rullzer Yes, the file size of the max is zero for the failed files I had so far.

I already read about all previews being generated from the max (which I think in general is a reasonable thing to do).
This bug also affects the preview generator app in the store (also tries to use the max, if it exists and crashes if the max is corrupt).

I think one can prevent this bug from happening by using the preview generator app from the beginning (creates previews in single thread so is less likely to crash, while the on-demand preview generation rapidly runs into the limit of threads possible on the Raspberry Pi and uses almost all of its RAM).

I will try the following workaround for fixing my existing Photo folders:

1. Delete all previews from filesystem
2. Update filecache for previews using occ files:scan-app-data
3. Run occ preview:generate-all after setting the sizes to the ones the Gallery needs (32 square and 256 height for desktop and 128 square and 1024 height for mobile, width set to 0 for not generating any previews according to this rule).

[rullzer]

Yes the preview generation app uses the same stuff from the server as the other preview routes use.

I'll see if we can catch this bad behaviour by checking the size of the max, and maybe even checking if the file is a valid image (if we try to resize).

I guess the easiest solution would be:

1. Check if the maxpreview has a size in https://github.com/nextcloud/server/blob/master/lib/private/Preview/Generator.php#L112
2. Convert https://github.com/nextcloud/server/blob/master/lib/private/Preview/Generator.php#L332

• Throw Not found exception instead of invalid argument (better to fail with a 404 I guess)
• Delete the max preview if it is invalid

This will cause that preview request to fail with a 404. But at least it will be fully generated next time it is requested. It should not happen that often anyways ;)

I'll take care of this once we are done with 13.

[streckus]

Sounds like a good plan :)

[ArnisR]

Sometimes other preview sizes are corrupted too. All of them had 0 size. So I just run cronjob every 30 min. which deletes preview files with 0 size. On next access they are regenerated fine.

find "/path_to_NC_appdata/preview" -size 0 -delete

[rullzer]

@ArnisR mmm can you check if they also have a size of zero in the filecache?

[ArnisR]

@rullzer Ok, I'll try. I deactivated cronjob and will take a look after when/if corrupted previews appears.