Fix mount for Node.js >= 15.1.0

[kyptin]

I tried the basic example in the README. It failed with a 500 Internal Server Error and the following JSON body:

{
    "message": "Cannot read properties of undefined (reading 'x-forwarded-proto')",
    "name": "TypeError"
}

The output from the server process includes a stack trace. Sanitized a bit, it is:

TypeError: Cannot read properties of undefined (reading 'x-forwarded-proto')
    at protocol (.../node_modules/paperplane/lib/parseUrl.js:18:14)
    at .../node_modules/ramda/src/converge.js:47:17
    at _map (.../node_modules/ramda/src/internal/_map.js:6:19)
    at .../node_modules/ramda/src/converge.js:46:33
    at f1 (.../node_modules/ramda/src/internal/_curry1.js:18:17)
    at .../node_modules/ramda/src/uncurryN.js:34:21
    at .../node_modules/ramda/src/internal/_curryN.js:37:27
    at .../node_modules/ramda/src/internal/_arity.js:10:19
    at .../node_modules/ramda/src/internal/_pipe.js:3:14
    at .../node_modules/ramda/src/internal/_arity.js:10:19

Yet the docker-based demo app works. That uses Node.js v12.22.12. When I tried that Node version on the basic example, it also worked.

So, I used nvm to do a binary search on versions. I identified that Node.js v15.1.0 is the first failing version, and every version I tried that was newer (up to v21.2.0) also failed.

Scouring the Node.js change log revealed that the http module of v15.1.0 started calculating req.headers lazily. There's a full discussion in nodejs/node#35281 [1]. Note the referenced issue that identifies the bug [2].

[1] nodejs/node#35281
[2] nodejs/node#36550

The workaround identified in this comment [3] is not to use the spread operator or Object.assign on the request object. "These objects are essentially uncloneable."

[3] nodejs/node#36550 (comment)

This is surprisingly tricky to do right. Various Ramda functions like merge (and I think converge) do this implicitly, as does funky's assocWith. So to work around this limitation, while preserving all behavior, I had to resort to (gasp) mutating procedures instead of pure functions. Not ideal, I know. I'm open to better ideas.

So, maybe this isn't the best solution, but it least it gets the example working again on modern Node versions. If it never gets merged, at least it will be findable via the repo on GitHub.

For reference, to test this, I used a fresh NPM project with only the paperplane dependency:

mkdir paperplane
cd paperplane
npm init -y
npm i -S paperplane

In which I added an index.js file with these contents:

const { compose } = require('ramda')
const http = require('http')
const { json, logger, methods, mount, routes } = require('paperplane')

const cookies = req => ({ cookies: req.cookies || 'none?' })
const hello   = req => ({ message: `Hello ${req.params.name}!` })

const app = routes({
  '/'           : methods({ GET: _ => ({ body: 'Hello anon.' }) }),
  '/cookies'    : methods({ GET: compose(json, cookies) }),
  '/hello/:name': methods({ GET: compose(json, hello) })
})

http.createServer(mount({ app })).listen(3000, logger)

And finally (with fd and entr and httpie installed), I started a file-watching auto-test process:

fd -e js | entr -rcc bash -c "node index.js & http -v get http://localhost:3000/cookies Cookie:foo=bar"

[kyptin]

It seems this patch breaks serve. I don't know why.