micro/selector/selector.go

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/*
The Selector package provides a way to algorithmically filter and return
nodes required by the client or any other system. Selector's implemented
by Micro build on the registry but it's of optional use. One could
provide a static Selector that has a fixed pool.
func (r *randomSelector) Select(service string, opts ...SelectOption) (Next, error) {
var sopts SelectOptions
for _, opt := range opts {
opt(&sopts)
}
// get the service
services, err := r.so.Registry.GetService(service)
if err != nil {
return nil, err
}
// apply the filters
for _, filter := range sopts.Filters {
services = filter(services)
}
// if there's nothing left, return
if len(services) == 0 {
return nil, ErrNotFound
}
var nodes []*registry.Node
for _, service := range services {
for _, node := range service.Nodes {
nodes = append(nodes, node)
}
}
if len(nodes) == 0 {
return nil, ErrNotFound
}
return func() (*registry.Node, error) {
i := rand.Int()
j := i % len(services)
if len(services[j].Nodes) == 0 {
return nil, ErrNotFound
}
k := i % len(services[j].Nodes)
return services[j].Nodes[k], nil
}, nil
}
*/
package selector
import (
"errors"
"github.com/micro/go-micro/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 {
// 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
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// Name of the selector
String() string
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}
// Next is a function that returns the next node
// based on the selector's algorithm
type Next func() (*registry.Node, error)
// SelectFilter is used to filter a service during the selection process
type SelectFilter func([]*registry.Service) []*registry.Service
var (
DefaultSelector = newRandomSelector()
ErrNotFound = errors.New("not found")
ErrNoneAvailable = errors.New("none available")
)
func NewSelector(opts ...Option) Selector {
return newRandomSelector(opts...)
}