Improve error message when a request is blocked (and maybe also if it fails in other ways)

[flying-sheep]

by naming a notebook “heatmap.ipynb”, I triggered an EasyList rule (/heatmap.*?) in uBlock, so a request to the following URL was apparently blocked: /api/contents/heatmap.ipynb?type=notebook

The end result was a nonsensical Error loading Notebook: error, which didn’t improve even after some fixes to error messages in master.

I’m filing this issue without all the misleading information in the original one: #1623

[flying-sheep]

To reproduce, install uBlock Origin and add a custom filter for /blockednotebook.*?, then try to open a notebook named blockednotebook.ipynb

[minrk]

Terrific, thanks for tracking down the cause, @flying-sheep!

[jbednar]

We just ran into this same issue by having a notebook named heatmap.ipynb, which still gives a very obscure error message:

Until I found this issue, I had no idea this was due to uBlock and not Jupyter, so it would be great if somehow Jupyter could give a more informative error message. There must be lots of other filenames that uBlock might object to based on some previous bad actor...

[flying-sheep]

FYI: #2443 has been fixed, but the unhelpful error can still happen for other blocked names, so I recommend to leave this open.

[jasongrout]

I don't know that we can do anything about ublock blocking web resources - that's totally outside our control and in the user's hands. We do already suggest in the documentation:

Try disabling any browser extensions and/or any Jupyter extensions you have installed.

Can you think of a way to surface that more visibly, or maybe expand on that in the documentation better?

[jbednar]

Sure, just make a more helpful error message than "Error loading notebook / Error". Even just making the message have some unique number or phrase would help, so that it becomes google-able, but ideally, if it's truly an error that Jupyter can say nothing about, then pointing to the documentation would be great. And if this is typically an error that happens with ad blockers, pointing to that specific section of the docs would be super helpful!

[flying-sheep]

Yeah, exactly that’s what I proposed in the title and original support. My proposal is

1. modify the Error message for API requests fail to include HTTP method, path and status
   (This will make both console and error popup more helpful)
2. in case a request to fetch notebook contents fail, add a line about possible ad blockers interfering

API request to /api/contents/heatmap.ipynb?type=notebook failed with HTTP status 404: not found

This failure indicates that an ad blocker might block your notebook’s name.

[jbednar]

Maybe:

API request to /api/contents/heatmap.ipynb?type=notebook failed with HTTP status 404: not found
Perhaps an ad blocker or other browser or Jupyter extension is preventing this notebook from being served?