HTTP 412 Errors when editing Officewiki
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	akosiaris
	Mar 9 2023, 2:46 PM

Description

Time of effort editing Sandbox in officewiki, ~2023-03-09T14:44

See:

Requests are to /w/api.php, response is HTTP 200 with this payload (prettified)

{
  "errors": [
    {
      "code": "visualeditor-docserver-http",
      "html": "<p>Error contacting the Parsoid/RESTBase server (HTTP 412): (no message)\n</p><!--__DTHASLEDECONTENT__--><!--__DTEMPTYTALKPAGE__-->",
      "module": "visualeditoredit"
    }
  ],
  "docref": "See https://office.wikimedia.org/w/api.php for API usage. Subscribe to the mediawiki-api-announce mailing list at &lt;https://lists.wikimedia.org/postorius/lists/mediawiki-api-announce.lists.wikimedia.org/&gt; for notice of API deprecations and breaking changes.",
  "servedby": "mw2358"
}

Details

Subject	Repo	Branch	Lines +/-
Re-apply "Restore proper ETag handling""	mediawiki/services/parsoid	REL1_40	+2 -11
Bump parsoid to 0.18.0-a2	mediawiki/vendor	master	+50 K -222 K
Re-apply "Restore proper ETag handling""	mediawiki/services/parsoid	master	+2 -11
ParsoidHandlerTest: check no etag is emitted perdefault	mediawiki/core	master	+5 -0
TransformHandler: Load stashed page bundle based on ETag.	mediawiki/core	master	+60 -14
Revert "TransformHandler: Load stashed page bundle based on ETag."	mediawiki/core	wmf/1.40.0-wmf.26	+6 -132
Revert "TransformHandler: Load stashed page bundle based on ETag."	mediawiki/core	master	+6 -132

Customize query in gerrit

Event Timeline

akosiaris created this task.Mar 9 2023, 2:46 PM

Restricted Application added a subscriber: Aklapper. · View Herald TranscriptMar 9 2023, 2:46 PM

akosiaris triaged this task as High priority.Mar 9 2023, 2:46 PM

ihurbain subscribed.Mar 9 2023, 2:49 PM

Officewiki does not use RESTBase.

akosiaris updated the task description. (Show Details)Mar 9 2023, 2:55 PM

Change 896028 had a related patch set uploaded (by Subramanya Sastry; author: Subramanya Sastry):

[mediawiki/core@master] Revert "TransformHandler: Load stashed page bundle based on ETag."

https://gerrit.wikimedia.org/r/896028

gerritbot added a project: Patch-For-Review.Mar 9 2023, 3:23 PM

Zabe subscribed.Mar 9 2023, 3:28 PM

cscott moved this task from Needs Triage to Bugs & Crashers on the Parsoid board.Mar 9 2023, 3:37 PM

FWIW, when I tried to edit an existing page on officewiki, it worked fine. When I tried to edit the same page again, it failed with a 412.

daniel claimed this task.Mar 9 2023, 3:50 PM

Change 896028 merged by jenkins-bot:

[mediawiki/core@master] Revert "TransformHandler: Load stashed page bundle based on ETag."

https://gerrit.wikimedia.org/r/896028

Maintenance_bot removed a project: Patch-For-Review.Mar 9 2023, 4:31 PM

Change 896030 had a related patch set uploaded (by Subramanya Sastry; author: Subramanya Sastry):

[mediawiki/core@wmf/1.40.0-wmf.26] Revert "TransformHandler: Load stashed page bundle based on ETag."

https://gerrit.wikimedia.org/r/896030

gerritbot added a project: Patch-For-Review.Mar 9 2023, 4:48 PM

Change 896030 merged by jenkins-bot:

[mediawiki/core@wmf/1.40.0-wmf.26] Revert "TransformHandler: Load stashed page bundle based on ETag."

https://gerrit.wikimedia.org/r/896030

Maintenance_bot removed a project: Patch-For-Review.Mar 9 2023, 5:30 PM

Mentioned in SAL (#wikimedia-operations) [2023-03-09T17:38:05Z] <zabe@deploy2002> Started scap: Backport for [[gerrit:896030|Revert "TransformHandler: Load stashed page bundle based on ETag." (T331629)]]

Mentioned in SAL (#wikimedia-operations) [2023-03-09T17:39:46Z] <zabe@deploy2002> zabe and ssastry: Backport for [[gerrit:896030|Revert "TransformHandler: Load stashed page bundle based on ETag." (T331629)]] synced to the testservers: mwdebug2002.codfw.wmnet, mwdebug1002.eqiad.wmnet, mwdebug1001.eqiad.wmnet, mwdebug2001.codfw.wmnet

Mentioned in SAL (#wikimedia-operations) [2023-03-09T17:50:02Z] <zabe@deploy2002> Finished scap: Backport for [[gerrit:896030|Revert "TransformHandler: Load stashed page bundle based on ETag." (T331629)]] (duration: 11m 57s)

ReleaseTaggerBot added a project: MW-1.40-notes (1.40.0-wmf.27; 2023-03-13).Mar 9 2023, 10:01 PM

ReleaseTaggerBot edited projects, added MW-1.40-notes (1.40.0-wmf.26; 2023-03-06); removed MW-1.40-notes (1.40.0-wmf.27; 2023-03-13).Mar 9 2023, 11:00 PM

Analysis:

on officewiki, VE is configured to use REST endpoints exposed by the Parsoid extension directly. It doesn't use the new "direct" mode yet (which would use internal PHP calls), nor does it use RESTbase (like most wikis at the moment).
In this mode, VE' getPageHTml() will hit the page/html endpoint exposed by the Parsoid extension. It will send the stash parameter, but the endpoint does not support this parameter. So content does not get stashed. It does however return an ETag that identifies the rendered HTML.
When saving content, VE will use that etag in transformHTML() to set the If-Match header, and send it to the transform/html/to/wikitext endpoint defiend by the Parsoid extension.
Per Ida81a314f015e205f2081c68a82d486145097c92, Parsoid's transform/ endpoint will try to load a rendering based on the etag content if an If-Match is present. This fails, since no content was stashed, and triggers a 412 response.

Open question:

when trying to load the content identified by the If-Match header, the HtmlOutputRendererHelper should fall back to checking the parser cache if no match is found in the stash. It's not clear why no matching output is found in the parser cache. The parser cache doesn't get written because TemporaryParsoidHandlerParserCacheWriteRatio is set. This is currently 50% and was set to 20% before, which explains why editing would sometimes work.

Possible fixes:

Make parsoid's page/html endpoint support the stash flag
Make parsoid's page/html endpoint return no etag (and hope RESTbase doesn't need it)
Make parsoid's transform/ endpoint ignore the etag
Switch officewiki to the new direct mode.

Config used to reproduce the issue locally:

wfLoadExtension( 'VisualEditor' );
$wgVisualEditorDefaultParsoidClient = 'vrs';
$wgTemporaryParsoidHandlerParserCacheWriteRatio = 0;

$wgVirtualRestConfig['modules']['parsoid'] = [
	'url' => "$wgServer/w/rest.php/",
	'prefix' => $wgDBname, // The wiki prefix to use; deprecated
	'domain' => $wgServer
];