adding support for specifying headers in ctx.onerror

[dead-horse]

koajs/ratelimit#13

[jonathanong]

what can't be done with middleware? streaming errors? if anything, i'd prefer the .onerror handler to be configurable.

[cesarandreu]

+1 to having .onerror configurable

[tejasmanohar]

another +1 for making .onerror configurable

[tejasmanohar]

@jonathanong what would this look like? would we just extend the onErrors API to allow passing in headers (keys) that should stay in the response this.res._headers? is the end goal for the user to be able to specify what headers should stay, what the values of the headers that stay are, and/or just if headers should be unset or not?

[jonathanong]

i'm not sure. i'm not sure what the problem reported is

[pensierinmusica]

At the bare minimum I think the user should be allowed to keep the headers that have been set up to when the error has been thrown if it's a user-level error, as I mentioned here: #537 (comment).

Then, whether this should be a default behavior, or set as an option it's debatable. Imho should be default but other people might think differently.

[felixfbecker]

Related #571

[jonathanong]

i think i like #571 solution better. if you agree @dead-horse , wanna close this?

otherwise, onerror could be configurable too. technically it should already be configurable - we just need to make it more user-friendly and document it.

[dead-horse]

SGTM