selector.go

// MIT License
//
// Copyright (c) 2020 Lack
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

// Package selector is a way to pick a list of service nodes
package selector

import (
	"errors"

	"github.com/vine-io/vine/core/registry"
)

// Selector builds on the registry as a mechanism to pick nodes
// and mark their status. This allows host pools and other things
// to be built using various algorithms.
type Selector interface {
	Init(opts ...Option) error
	Options() Options
	// Select returns a function which should return the next node
	Select(service string, opts ...SelectOption) (Next, error)
	// Mark sets the success/error against a node
	Mark(service string, node *registry.Node, err error)
	// Reset returns state back to zero for a service
	Reset(service string)
	// Close renders the selector unusable
	Close() error
	// Name of the selector
	String() string
}

// Next is a function that returns the next node
// based on the selector's strategy
type Next func() (*registry.Node, error)

// Filter is used to filter a service during the selection process
type Filter func([]*registry.Service) []*registry.Service

// Strategy is a selection strategy e.g random, round robin
type Strategy func([]*registry.Service) Next

var (
	DefaultSelector = NewSelector()

	ErrNotFound      = errors.New("not found")
	ErrNoneAvailable = errors.New("none available")
)