Viewer builds incorporating CEF 139 results in transient errors at page load

[callumlinden]

Environment

Internal test build of Viewer from this PR

Might be Windows only - the macOS build is too slow to test right now

Description

After CEF 139 was incorporated into a test Viewer, it was noticed that various pages (most often the Viewer login page) result in a short transient error being displayed, before the content resolves as expected.

• Other people apart from myself have seen it so it's not my network
• It appears to have started after CEF version 134
• When the error occurs, CefBrowserHandler::onLoadError() is triggered
  • Note, historically this was often triggered with a value of ERR_ABORT (-3) which according to the official instructions, can be safely ignored. The errors we see in this issue are different - often -15.
• It was been seen outside of the Viewer in the Dullahan test app
• It has been seen for other non-Linden URLs but it happens less frequently
• Tried adding a handler for CefRequesatContext::onRequestContextInitialized() and proceeding with the application after that completes but that didn't appear to help

What is left to try?

• Not much sadly but this on my list:
• Write something to only update the memory buffer when an HTTP status code of 200 (maybe) is received. Since the error does resolve in a short period, this would just appear as a slight delay loading a page and the error would never be displayed.
• Write a small, terminal based CEF app that illustrates the issue. Text only. No Viewer. No textures. Shouldn't take more than a day. It might tell me something and if not, more likely to get help from other CEF people than asking them to build the Viewer.
• "Hope it goes away in a later version of CEF" - pretty thin!

Reproduction steps

Simply start the Viewer - about 20% of the time, you see the transient error before the login page resolves.

Example:

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[vldevel]

Might be Windows only

Nope, it also happens under Linux (both x86_64 and aarch64 too).

Since I'm using every new stable CEF release for the Cool VL Viewer under Linux (I build x86_64 CEF myself, and use Spotify's builds for aarch64 viewer builds), I can confirm that this bug has been occurring for a while (indeed sometime around CEF 135 releases) under Linux, and indeed seems to only affect SL login page (or at least, I did not see occurring with any other website).