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middleware.go
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middleware.go
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// Copyright (c) 2017 - The Event Horizon authors.
//
// Licensed 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 async
import (
"context"
"fmt"
eh "github.com/looplab/eventhorizon"
)
// NewMiddleware returns a new async handling middleware that returns any errors
// on a error channel.
func NewMiddleware() (eh.EventHandlerMiddleware, chan Error) {
errCh := make(chan Error, 20)
return eh.EventHandlerMiddleware(func(h eh.EventHandler) eh.EventHandler {
return &eventHandler{h, errCh}
}), errCh
}
type eventHandler struct {
eh.EventHandler
errCh chan Error
}
// HandleEvent implements the HandleEvent method of the EventHandler.
func (h *eventHandler) HandleEvent(ctx context.Context, event eh.Event) error {
go func() {
if err := h.EventHandler.HandleEvent(ctx, event); err != nil {
// Always try to deliver errors.
h.errCh <- Error{err, ctx, event}
}
}()
return nil
}
// Error is an async error containing the error and the event.
type Error struct {
// Err is the error that happened when handling the event.
Err error
// Ctx is the context used when the error happened.
Ctx context.Context
// Event is the event handeled when the error happened.
Event eh.Event
}
// Error implements the Error method of the error interface.
func (e Error) Error() string {
return fmt.Sprintf("%s: %s", e.Event.String(), e.Err.Error())
}