Use of `res.end` is preventing other middleware from completing in Node

I’m running into an issue where I use express-openid-connect and both that package and ApolloServer conflict:

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
    at new NodeError (node:internal/errors:329:5)
    at ServerResponse.setHeader (node:_http_outgoing:573:11)
    at ServerResponse.header (/Users/davedash/Projects/backend/node_modules/express/lib/response.js:771:10)
    at ServerResponse.append (/Users/davedash/Projects/backend/node_modules/express/lib/response.js:732:15)
    at ServerResponse.res.cookie (/Users/davedash/Projects/backend/node_modules/express/lib/response.js:857:8)
    at setCookie (/Users/davedash/Projects/backend/node_modules/express-openid-connect/lib/appSession.js:135:13)
    at CookieStore.set (/Users/davedash/Projects/backend/node_modules/express-openid-connect/lib/appSession.js:150:7)
    at ServerResponse.resEnd [as end] (/Users/davedash/Projects/backend/node_modules/express-openid-connect/lib/appSession.js:295:21)
    at /Users/davedash/Projects/backend/node_modules/apollo-server-express/dist/ApolloServer.js:135:25
    at Layer.handle [as handle_request] (/Users/davedash/Projects/backend/node_modules/express/lib/router/layer.js:95:5)

Not 100% sure what’s happening, but it seems like some cookies are trying to be set by express-openid-connect and maybe that middleware is running at the same time as the playground code. So when we get to here:

https://github.com/apollographql/apollo-server/blob/a3282a2d7df0c20d9e10b058defae835120fa5b1/packages/apollo-server-express/src/ApolloServer.ts#L202

We end the response and express gives us the above error.

I was able to temporarily fix this by changing that line to res.send(playground) and removing the res.write and res.end calls.

Unfortunately, since I don’t know what’s really happening, I don’t feel confident publishing that as a pull request - and I’m wondering if there’s a better way to handle this.

[davedash]

@glasser you rock.

I’m posting this - just on the off chance someone runs into the same issues as I.

1. I created the code sandbox per your suggestion. The minimal implementation I thought should fail, did not.
2. So I pulled that all into my own repo and of course it failed for me.
3. So I dug into the details, and it seemed some packages were slightly different.
4. Upgraded a few packages via yarn
5. It works locally.

Thanks for the suggestion, it really helped me narrow it down quickly.

[glasser]

It sounds like perhaps the way you’ve integrated express-openid-connect and apollo-server-express conflict with each other? Perhaps you need to make sure that the other package runs before Apollo Server or only when Apollo Server handlers aren’t running? I won’t be able to help debug without actually being able to reproduce the issue on my own machine. I’ll be happy to reopen this issue if you provide a full reproduction that doesn’t require me to be creative at all to try it out: a series of instructions (probably including git clone or using something on codesandbox.io) that shows the issue to me.