Lesson 24 · Return 404 for unknown paths

Return 404 for unknown paths

When no route matches, the server must say so with a 404 rather than crashing on a missing handler. Today you add that fallback to the router.

The goal

Dispatch to a 404 Not Found response when no registered route matches the request.

Start here - the target

TO DO

Scenario: No route matches

Givena router with only GET "/" registered

Whena request for GET "/missing" is dispatched

Thenthe response status is 404 and the body is "Not Found"

Background

Looking a route up in a map has two outcomes, and until now you only handled one. When the key is absent, indexing a Go map returns a nil handler that panics when called — so the router must check whether the route exists and, when it does not, produce a 404 Not Found itself.

This is the first status code the server chooses on its own rather than always returning 200. The reason phrase comes free from the table you seeded in lesson 18. A missing route is now a clean, well-formed response instead of a dropped connection.

Make it work

h, ok := m.routes[key(r.Method, r.Path)]
if !ok {
    return Response{Status: 404, Body: []byte("Not Found")}
}
return h(r)

CheckpointDONE

Unknown paths return a clean 404. Commit.