Function exercise4

codelab/solution/codelab.go:156–197

exercise4 demonstrates how to extend CEL with custom functions. Declare a `contains` member function on map types that returns a boolean indicating whether the map contains the key-value pair.

()

// Declare a `contains` member function on map types that returns a boolean
// indicating whether the map contains the key-value pair.
func exercise4() {
	fmt.Println("=== Exercise 4: Customization ===\n")
	// Determine whether an optional claim is set to the proper value. The custom
	// map.contains(key, value) function is used as an alternative to:
	//   key in map && map[key] == value

	// Useful components of the type-signature for 'contains'.
	typeParamA := cel.TypeParamType("A")
	typeParamB := cel.TypeParamType("B")
	mapAB := cel.MapType(typeParamA, typeParamB)

	// Env declaration.
	env, _ := cel.NewEnv(
		cel.Types(&rpcpb.AttributeContext_Request{}),
		// Declare the request.
		cel.Variable("request",
			cel.ObjectType("google.rpc.context.AttributeContext.Request"),
		),
		// Declare the custom contains function and its implementation.
		cel.Function("contains",
			cel.MemberOverload("map_contains_key_value",
				[]*cel.Type{mapAB, typeParamA, typeParamB},
				cel.BoolType,
				cel.FunctionBinding(mapContainsKeyValue)),
		),
	)
	ast := compile(env,
		`request.auth.claims.contains('group', 'admin')`,
		cel.BoolType)

	// Construct the program plan.
	// Output: false
	program, err := env.Program(ast)
	if err != nil {
		glog.Exit(err)
	}

	eval(program, request(auth("user:me@acme.co", emptyClaims), time.Now()))
	claims := map[string]string{"group": "admin"}
	eval(program, request(auth("user:me@acme.co", claims), time.Now()))
	fmt.Println()
}

// exercise5 covers how to build complex objects as CEL literals.
//