output_wrapper.go

/*
Copyright (c) 2014 Ashley Jeffs

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 buffer

import (
	"sync"
	"sync/atomic"
	"time"

	"github.com/jeffail/benthos/lib/buffer/impl"
	"github.com/jeffail/benthos/lib/types"
	"github.com/jeffail/util/metrics"
)

//------------------------------------------------------------------------------

// OutputWrapper - Wraps a buffer with a Producer/Consumer interface.
type OutputWrapper struct {
	stats metrics.Type

	buffer impl.Buffer

	running int32

	messagesIn   <-chan types.Message
	messagesOut  chan types.Message
	responsesIn  <-chan types.Response
	responsesOut chan types.Response
	errorsChan   chan []error

	closedWG sync.WaitGroup

	closeChan  chan struct{}
	closedChan chan struct{}
}

// NewOutputWrapper - Create a new Producer/Consumer around a buffer.
func NewOutputWrapper(buffer impl.Buffer, stats metrics.Type) Type {
	m := OutputWrapper{
		stats:        stats,
		buffer:       buffer,
		running:      1,
		messagesOut:  make(chan types.Message),
		responsesOut: make(chan types.Response),
		errorsChan:   make(chan []error),
		closeChan:    make(chan struct{}),
		closedChan:   make(chan struct{}),
	}

	return &m
}

//------------------------------------------------------------------------------

// inputLoop - Internal loop brokers incoming messages to the buffer.
func (m *OutputWrapper) inputLoop() {
	defer func() {
		close(m.responsesOut)
		m.buffer.CloseOnceEmpty()
		m.closedWG.Done()
	}()

	for atomic.LoadInt32(&m.running) == 1 {
		var msg types.Message
		var open bool
		select {
		case msg, open = <-m.messagesIn:
			if !open {
				return
			}
		case <-m.closeChan:
			return
		}
		backlog, err := m.buffer.PushMessage(msg)
		if err == nil {
			m.stats.Gauge("buffer.backlog", int64(backlog))
		}
		select {
		case m.responsesOut <- types.NewSimpleResponse(err):
		case <-m.closeChan:
			return
		}
	}
}

// outputLoop - Internal loop brokers buffer messages to output pipe.
func (m *OutputWrapper) outputLoop() {
	defer func() {
		m.buffer.Close()
		close(m.messagesOut)
		close(m.errorsChan)
		m.closedWG.Done()
	}()

	errs := []error{}
	errMap := map[error]struct{}{}

	var msg types.Message
	for atomic.LoadInt32(&m.running) == 1 {
		if msg.Parts == nil {
			var err error
			if msg, err = m.buffer.NextMessage(); err != nil {
				if err != types.ErrTypeClosed {
					// Unconventional errors here should always indicate some sort of corruption.
					// Hopefully the corruption was message specific and not the whole buffer, so we
					// can try shifting and reading again.
					m.buffer.ShiftMessage()
					if _, exists := errMap[err]; !exists {
						errMap[err] = struct{}{}
						errs = append(errs, err)
					}
				} else {
					// If our buffer is closed then we exit.
					return
				}
			}
		}

		if msg.Parts != nil {
			select {
			case m.messagesOut <- msg:
			case <-m.closeChan:
				return
			}
			res, open := <-m.responsesIn
			if !open {
				return
			}
			if res.Error() == nil {
				msg = types.Message{}
				backlog, _ := m.buffer.ShiftMessage()
				m.stats.Gauge("buffer.backlog", int64(backlog))
			} else {
				if _, exists := errMap[res.Error()]; !exists {
					errMap[res.Error()] = struct{}{}
					errs = append(errs, res.Error())
				}
			}
		}

		// If we have errors built up.
		if len(errs) > 0 {
			select {
			case m.errorsChan <- errs:
				errMap = map[error]struct{}{}
				errs = []error{}
			default:
				// Reader not ready, do not block here.
			}
		}
	}
}

// StartReceiving - Assigns a messages channel for the output to read.
func (m *OutputWrapper) StartReceiving(msgs <-chan types.Message) error {
	if m.messagesIn != nil {
		return types.ErrAlreadyStarted
	}
	m.messagesIn = msgs

	if m.responsesIn != nil {
		m.closedWG.Add(2)
		go m.inputLoop()
		go m.outputLoop()
		go func() {
			m.closedWG.Wait()
			close(m.closedChan)
		}()
	}
	return nil
}

// MessageChan - Returns the channel used for consuming messages from this input.
func (m *OutputWrapper) MessageChan() <-chan types.Message {
	return m.messagesOut
}

// StartListening - Sets the channel for reading responses.
func (m *OutputWrapper) StartListening(responses <-chan types.Response) error {
	if m.responsesIn != nil {
		return types.ErrAlreadyStarted
	}
	m.responsesIn = responses

	if m.messagesIn != nil {
		m.closedWG.Add(2)
		go m.inputLoop()
		go m.outputLoop()
		go func() {
			m.closedWG.Wait()
			close(m.closedChan)
		}()
	}
	return nil
}

// ResponseChan - Returns the response channel.
func (m *OutputWrapper) ResponseChan() <-chan types.Response {
	return m.responsesOut
}

// ErrorsChan - Returns the errors channel.
func (m *OutputWrapper) ErrorsChan() <-chan []error {
	return m.errorsChan
}

// CloseAsync - Shuts down the OutputWrapper and stops processing messages.
func (m *OutputWrapper) CloseAsync() {
	if atomic.CompareAndSwapInt32(&m.running, 1, 0) {
		close(m.closeChan)
	}
}

// WaitForClose - Blocks until the OutputWrapper output has closed down.
func (m *OutputWrapper) WaitForClose(timeout time.Duration) error {
	select {
	case <-m.closedChan:
	case <-time.After(timeout):
		return types.ErrTimeout
	}
	return nil
}

//------------------------------------------------------------------------------