Colliding routes causes params to be undefined in route handler

[ajaco]

Hi!

I was working on a project and I found some odd behaviour while using Fastify. I managed to reproduce it in find-my-way, so here goes.

Given the following routes, each with their own handler:

• GET /foo/:id (handler 1)
• GET /foo/:color/:id (handler 2)
• GET /foo/red (handler3)

If you then do a GET /foo/red/123, the correct handler (handler 2) will be invoked.
The id-param will correctly be '123', but the color param is undefined.

If you do a GET /foo/blue/123, both params are correct (blue, 123).

Handler 3 is still correctly invoked for GET /foo/red. So the routing is correct, but the params are wrong.

If you unregister GET /foo/red the /foo/:color/:id route will then work again with red.

I created a fork of the repo with a unit test to illustrate the problem: ajaco@8b48949

That test will fail with the following output:

So I'm not sure if this is a bug or intended, but I found it very odd. Hopefully this issue will either highlight a bug, or make me understand this behaviour.

[Eomm]

It seems related to fastify/fastify#2261

[mcollina]

The solution is to:

GET /foo/:id (handler 1)
GET /foo/:color/:id (handler 2) <-- same handler
GET /foo/red (handler3)
GET /foo/red/:id (handler 2) <-- same handler

[ajaco]

The solution is to:

GET /foo/:id (handler 1)
GET /foo/:color/:id (handler 2) <-- same handler
GET /foo/red (handler3)
GET /foo/red/:id (handler 2) <-- same handler

This does not solve the problem.

If you request GET /foo/red/123, req.params will look like this: {id: '123'}.

So while you, in this specific case, can infer that color missing from the req.params means that its value is actually red, that is not sustainable. What happens if you register the following routes:

GET /foo/:id (handler 1)
GET /foo/:color/:id (handler 2) <-- same handler
GET /foo/red (handler3)
GET /foo/red/:id (handler 2) <-- same handler
GET /foo/blue (handler 4) 
GET /foo/blue/:id (handler 2) <-- same handler

If someone requests /foo/red/123 now, how do you know its red? It could be blue as well now.

[mcollina]

If you are using fastify, you can find the options you have passed in when creating the routes as req.context.config.

[mcollina]

You can also set a default for the color param with configuring a schema for the params: https://www.fastify.io/docs/latest/Validation-and-Serialization/#validation.

[ivan-tymoshenko]

This issue was fixed. I added a test here #262. We can close this.