Error Handling Middleware

[danieladams456]

Is this a feature request?

Yes

http-proxy events forces you to handle writing the response within the handler onError(err, req, res) instead of allowing you to pass it to an Express error handling middleware.

Motivation: I have a standard Express middleware that handles error response formatting for the rest of the app (authentication errors, etc). My app is simple and that logic is just a few lines of code, but it would be nice especially for more complex apps not to have to duplicate that logic. I am also using NewRelic APM and it can more easily deduce errors when they flow through an Express error handling middleware. Again, nothing a few lines of manual code couldn't fix, but the ability to delegate to an error handling middleware would be ideal.

I'm not sure if there is a clean way of handling this without monkey-patching or something since http-proxy wasn't designed to be tied to Express.

Steps to reproduce

1. There is no next argument for a next(err) call in the http-proxy onError event function signature.

Expected behavior

Feature request to investigate whether there is a clean solution to extend that function call signature with another argument that would let the remainder of the request flow through Express' standard error handling middleware.

Actual behavior

http-proxy-middleware must fully write the response, including HTTP headers, etc.

Setup

• http-proxy-middleware: 0.19.0
• http-proxy-middleware configuration: see below
• server: express 4.16.4

const app = express();
app.use(healthMiddleware);
app.use(authMiddleware);
app.use(proxy({target: PROXY_TARGET, onError}));
app.use(errorMiddleware);

[chimurai]

Sounds interesting @danieladams456.

I'll have to investigate this.
Do you have a proposal for a generic solution?

[danieladams456]

I'm not sure how the stack/scoping works out, but theoretically could next be bound to the 4th/last argument in the onError function using lodash bind? (credit) I see lodash is already a dependency.

[jardakotesovec]

Having next available in onError sounds good to me. I am also struggling with similar use case, where the failures inside the proxy were not caught with my error handler.

[OliverJAsh]

Potentially related: webpack/webpack-dev-server#2380

[hpl002]

Any update on this?

I too have other downstream middleware that is not triggered because the response is ended in the proxy instead of being passed along.