1309235 - about:support is blank, with console error about osfile/lz failure

Status: RESOLVED WONTFIX

(Toolkit Graveyard :: OS.File, defect)

Description

[Benjamin Smedberg]

My about:support won't load, windows 10. It's mostly-blank. In the past that has been caused by JS errors in/under Troubleshoot.jsm

A promise chain failed to handle a rejection. Did you forget to '.catch', or did you forget to 'return'?
See https://developer.mozilla.org/Mozilla/JavaScript_code_modules/Promise.jsm/Promise

Date: Tue Oct 11 2016 16:35:55 GMT+0300 (FLE Standard Time)
Full Message: Error: uncaught exception: Invalid header (no magic number
Full Stack: postMessage@resource://gre/modules/PromiseWorker.jsm:325:17
TaskImpl_run@resource://gre/modules/Task.jsm:323:42
Handler.prototype.process@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:940:21
this.PromiseWalker.walkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:816:7
Promise*this.PromiseWalker.scheduleWalkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:747:11
this.PromiseWalker.schedulePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:779:7
this.PromiseWalker.completePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:714:7
get _worker/worker.onerror@resource://gre/modules/PromiseWorker.jsm:198:7
EventHandlerNonNull*get _worker@resource://gre/modules/PromiseWorker.jsm:194:5
postMessage@resource://gre/modules/PromiseWorker.jsm:291:9
TaskImpl_run@resource://gre/modules/Task.jsm:322:42
Handler.prototype.process@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:937:23
this.PromiseWalker.walkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:816:7
Promise*this.PromiseWalker.scheduleWalkerLoop@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:747:11
this.PromiseWalker.schedulePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:779:7
this.PromiseWalker.completePromise@resource://gre/modules/Promise.jsm -> resource://gre/modules/Promise-backend.js:714:7
onError@resource://gre/modules/osfile/osfile_native.jsm:66:7

That points at http://searchfox.org/mozilla-central/rev/e8dd21b1673c07307068303ab3e99360c78f4d12/toolkit/components/osfile/modules/osfile_native.jsm#66
The actual error is coming from here though: http://searchfox.org/mozilla-central/rev/e8dd21b1673c07307068303ab3e99360c78f4d12/toolkit/components/lz4/lz4.js#115

Yoric, if I were to try and catch this in a JS debugger, would it help to break at lz4.js to see which file it's trying to access? And similarly, can I figure out where in Troubleshoot.jsm this ends up breaking stuff?

Comment 1

[David Teller [:Yoric] - still alive but not very active]

Apparently, this error was raised in a ChromeWorker. I don't know if the JS debugger can handle those.

The error message seems relatively understandable: "Error: uncaught exception: Invalid header (no magic number)". At this stage, my guess is that the file is empty and that the calling code doesn't handle the error gracefully.

There is no straightforward way to find the exact file (which we should fix). The simplest way for debugging would probably be to catch an error in AbstractFile.read in the Lz4 branch and enrich the error message with the path: http://searchfox.org/mozilla-central/source/toolkit/components/osfile/modules/osfile_shared_front.jsm#329

A better way would be to tweak lz4.js so that it accepts as argument the file name and use it when building the error message.

Comment 2

[David Teller [:Yoric] - still alive but not very active]

Filed the underlying OS.File bug as mentored bug 1309249.

Comment 3

[:Gijs (out until Jan 5th; he/him)]

Is this a regression? As in, if this is broken in a clean profile, is it broken in a clean profile on release?

Comment 4

[Benjamin Smedberg]

This does not affect a clean profile, so I don't know whether this is a code regression or not.

Comment 5

[Beth Rennie [:beth] (she/her)]

OS.File is pending removal