When subclassing a JS error, most browsers include the constructor
stacktrace :/
This is an issue, because:
- The stacktrace is deeper than it should be
- The stacktrace reaches into a polyfill for which there is not source
map, which causes Sentry to infer the issue grouping from the JS file
name. And the fingerprinted name changes on each release. So for each
release, the stacktrace is different ; and Sentry can't group issues
properly.
We have quite a lot of `Error reading file` errors when uploading files.
These errors are generated by ActiveStorage `file_checksum.js` component
but it eats the actual reason of errors.
(See https://github.com/rails/rails/blob/5-2-stable/activestorage/app/javascript/activestorage/file_checksum.js#L38)
We can't really override the class to generate better errors, as they
are deeply nested in ActiveStorage class hierarchy, and not exported to
external code.
Instead, we hook into the FileReader event handler, to insert a logger
when this error occur. The original event handler will also still be
called as usual.
This is intended to be temporary. The debug code will be removed once
we get a better idea of what is going on.
A DirectUpload may fail for several reasons, and return many types of
errors (string, xhr response, Error objects, etc).
For convenience, wrap all these errors in a FileUploadError object.
- It makes easier for clients of the Uploader class to handle errors;
- It allows to propagate the error code and failure responsability.
DirectUpload returns errors as strings, including an HTTP status and a
file name (and without a stack trace).
But Sentry groups issues according to the stack trace, and maybe the
error message in last resort.
So we have an issue: as all DirectUpload errors logged by Sentry are
generated on the same line, with random-looking messages, Sentry groups
them either too or too little aggressively.
Instead of creating all the errors on the same line:
- add some `if`s statements to create them on different lines (and so
with different stack traces),
- strip the file name from the error message.
This allows Sentry to group the errors properly, with meaningful error
messages.
When the authenticity token is invalid, the creation of the blob before
the direct upload returns a 422.
In that case, the token will never become valid again, and it is useless
to try again. Don’t show the "Retry" button in this case.
NB: of course the real fix is to understand why the authenticity token
is so often invalid – but this will be for later.
Pooling for attachment status is a background operation. Errors should
not be reported to the user, who didn't even ask for this operation to
take place.
This is why we ignore all errors, whether Javascript exceptions or
network errors.
