Predicate

What I do

• Create predicate code that is efficient and readable

When to use me

Use this when you are writing code in sub-folders of ./predicates/. Some predicates are also located in the ./routing/ folder for historical reasons.

Quick start

A predicate consists of 2 types spec and predicate that implement 2 different interfaces:

// PredicateSpec instances are used to create custom predicates
// (of type Predicate) with concrete arguments during the
// construction of the routing tree.
type PredicateSpec interface {

	// Name of the predicate as used in the route definitions.
	Name() string

	// Creates a predicate instance with concrete arguments.
	Create([]any) (Predicate, error)
}

// Predicate instances are used as custom user defined route
// matching predicates.
type Predicate interface {

	// Returns true if the request matches the predicate.
	Match(*http.Request) bool
}

The Create([]any) (Predicate, error) function is run at routing tree creation time, so only once in a while. Everything we can pre-compute to run a faster Match(*http.Request) bool execution the better. Here we process input from developers or operators that might do mistakes. We want to show errors clearly.

The Predicate interface function Match(*http.Request) bool is running in the hotpath of the request processing. Here we need to be very efficient and want to reduce latency, increase throughput, minimize allocations and we run heavily concurrent. Every request will be proceesed by a lot of Predicates and so each Match needs to be as fast as possible.