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registry.go
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registry.go
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// Licensed to Elasticsearch B.V. under one or more contributor
// license agreements. See the NOTICE file distributed with
// this work for additional information regarding copyright
// ownership. Elasticsearch B.V. licenses this file to you under
// the Apache License, Version 2.0 (the "License"); you may
// not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied. See the License for the
// specific language governing permissions and limitations
// under the License.
package registry
import (
"fmt"
"reflect"
"github.com/elastic/go-ucfg"
"github.com/andrewkroh/go-sawmill/pkg/processor"
)
var (
errorInterface = reflect.TypeOf((*error)(nil)).Elem()
processorInterface = reflect.TypeOf((*processor.Processor)(nil)).Elem()
)
var constructors = NewRegistry()
func MustRegister(name string, constructorFunc interface{}) {
if err := constructors.Register(name, constructorFunc); err != nil {
panic(err)
}
}
func NewProcessor(name string, config map[string]interface{}) (processor.Processor, error) {
return constructors.NewProcessor(name, config)
}
type processorConstructor struct {
// newConfig returns a pointer to a zero value config.
newConfig func() reflect.Value
newProc func(config reflect.Value) (processor.Processor, error)
}
type Registry struct {
procs map[string]processorConstructor
}
func NewRegistry() *Registry {
return &Registry{procs: map[string]processorConstructor{}}
}
func (r *Registry) Register(name string, constructorFunc interface{}) error {
if _, found := r.procs[name]; found {
return fmt.Errorf("%q processor is already registered", name)
}
pc, err := validateConfig(constructorFunc)
if err != nil {
return err
}
r.procs[name] = *pc
return nil
}
func (r *Registry) NewProcessor(name string, config map[string]interface{}) (processor.Processor, error) {
pc, found := r.procs[name]
if !found {
return nil, fmt.Errorf("processor type %q not found", name)
}
procConfigValue := pc.newConfig()
uConf, err := ucfg.NewFrom(config)
if err != nil {
return nil, err
}
if err := uConf.Unpack(procConfigValue.Interface()); err != nil {
return nil, err
}
return pc.newProc(procConfigValue)
}
func (r *Registry) clear() {
r.procs = map[string]processorConstructor{}
}
func validateConfig(i interface{}) (*processorConstructor, error) {
v := reflect.ValueOf(i)
t := v.Type()
if t.Kind() != reflect.Func {
return nil, fmt.Errorf("value must be a function, but got %v", t.Kind())
}
// Check config.
if t.NumIn() != 1 {
return nil, fmt.Errorf("function must accept one arg")
}
configType := t.In(0)
if configType.Kind() != reflect.Struct {
return nil, fmt.Errorf("function must be config struct")
}
if t.NumOut() != 2 {
return nil, fmt.Errorf("function must return 2 values")
}
processorType := t.Out(0)
if processorType.Kind() != reflect.Ptr {
return nil, fmt.Errorf("function should return a pointer to a processor struct")
}
if !processorType.Implements(processorInterface) {
return nil, fmt.Errorf("processor must implement processor.Processor")
}
errorType := t.Out(1)
if !errorType.Implements(errorInterface) {
return nil, fmt.Errorf("function should return an error")
}
pc := &processorConstructor{
newConfig: func() reflect.Value {
return reflect.New(configType)
},
newProc: func(config reflect.Value) (processor.Processor, error) {
if config.Type().Kind() == reflect.Ptr {
config = config.Elem()
}
out := v.Call([]reflect.Value{config})
if !out[1].IsNil() {
return nil, out[1].Interface().(error)
}
return out[0].Interface().(processor.Processor), nil
},
}
v.Call([]reflect.Value{reflect.New(configType).Elem()})
// TODO: Validate that each processor implements a 'Conifg() struct' method.
return pc, nil
}