Express-Style Handlers in Go: Fiber's Adapter That Nobody Expected
If you have ever tried to migrate a project from Express.js to Go, you know the friction. It is not the language syntax or the type system. It is that every HTTP handler follows a completely different convention. Express gives you (req, res, next). Go's standard library gives you (w, r). Fiber gives you (c) error. The logic is the same, but the shape is different, and reshaping hundreds of handlers is tedious, error-prone work.
Fiber v3 decided to stop pretending this is not a problem. Its handler adapter accepts seventeen different function signatures — from Fiber-native to Express-style callbacks to raw net/http and fasthttp handlers. You can mix them in the same application without manual wrapping.
This sounds like magic. It is actually a carefully designed type switch in adapter.go that performs this adaptation at runtime when routes are registered, instead of forcing you to do it by hand.