Queue: Add generic graceful queues with settings

modules/queue/queue.go

@@ -0,0 +1,128 @@
+// Copyright 2019 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package queue
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"reflect"
+)
+
+// ErrInvalidConfiguration is called when there is invalid configuration for a queue
+type ErrInvalidConfiguration struct {
+	cfg interface{}
+	err error
+}
+
+func (err ErrInvalidConfiguration) Error() string {
+	if err.err != nil {
+		return fmt.Sprintf("Invalid Configuration Argument: %v: Error: %v", err.cfg, err.err)
+	}
+	return fmt.Sprintf("Invalid Configuration Argument: %v", err.cfg)
+}
+
+// IsErrInvalidConfiguration checks if an error is an ErrInvalidConfiguration
+func IsErrInvalidConfiguration(err error) bool {
+	_, ok := err.(ErrInvalidConfiguration)
+	return ok
+}
+
+// Type is a type of Queue
+type Type string
+
+// Data defines an type of queuable data
+type Data interface{}
+
+// HandlerFunc is a function that takes a variable amount of data and processes it
+type HandlerFunc func(...Data)
+
+// NewQueueFunc is a function that creates a queue
+type NewQueueFunc func(handler HandlerFunc, config interface{}, exemplar interface{}) (Queue, error)
+
+// Shutdownable represents a queue that can be shutdown
+type Shutdownable interface {
+	Shutdown()
+	Terminate()
+}
+
+// Queue defines an interface to save an issue indexer queue
+type Queue interface {
+	Run(atShutdown, atTerminate func(context.Context, func()))
+	Push(Data) error
+}
+
+// DummyQueueType is the type for the dummy queue
+const DummyQueueType Type = "dummy"
+
+// NewDummyQueue creates a new DummyQueue
+func NewDummyQueue(handler HandlerFunc, opts, exemplar interface{}) (Queue, error) {
+	return &DummyQueue{}, nil
+}
+
+// DummyQueue represents an empty queue
+type DummyQueue struct {
+}
+
+// Run starts to run the queue
+func (b *DummyQueue) Run(_, _ func(context.Context, func())) {}
+
+// Push pushes data to the queue
+func (b *DummyQueue) Push(Data) error {
+	return nil
+}
+
+func toConfig(exemplar, cfg interface{}) (interface{}, error) {
+	if reflect.TypeOf(cfg).AssignableTo(reflect.TypeOf(exemplar)) {
+		return cfg, nil
+	}
+
+	configBytes, ok := cfg.([]byte)
+	if !ok {
+		configStr, ok := cfg.(string)
+		if !ok {
+			return nil, ErrInvalidConfiguration{cfg: cfg}
+		}
+		configBytes = []byte(configStr)
+	}
+	newVal := reflect.New(reflect.TypeOf(exemplar))
+	if err := json.Unmarshal(configBytes, newVal.Interface()); err != nil {
+		return nil, ErrInvalidConfiguration{cfg: cfg, err: err}
+	}
+	return newVal.Elem().Interface(), nil
+}
+
+var queuesMap = map[Type]NewQueueFunc{DummyQueueType: NewDummyQueue}
+
+// RegisteredTypes provides the list of requested types of queues
+func RegisteredTypes() []Type {
+	types := make([]Type, len(queuesMap))
+	i := 0
+	for key := range queuesMap {
+		types[i] = key
+		i++
+	}
+	return types
+}
+
+// RegisteredTypesAsString provides the list of requested types of queues
+func RegisteredTypesAsString() []string {
+	types := make([]string, len(queuesMap))
+	i := 0
+	for key := range queuesMap {
+		types[i] = string(key)
+		i++
+	}
+	return types
+}
+
+// CreateQueue takes a queue Type and HandlerFunc some options and possibly an exemplar and returns a Queue or an error
+func CreateQueue(queueType Type, handlerFunc HandlerFunc, opts, exemplar interface{}) (Queue, error) {
+	newFn, ok := queuesMap[queueType]
+	if !ok {
+		return nil, fmt.Errorf("Unsupported queue type: %v", queueType)
+	}
+	return newFn(handlerFunc, opts, exemplar)
+}