combine.go

// Copyright (c) 2017 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 processor

import (
	"github.com/Jeffail/benthos/lib/log"
	"github.com/Jeffail/benthos/lib/message"
	"github.com/Jeffail/benthos/lib/metrics"
	"github.com/Jeffail/benthos/lib/response"
	"github.com/Jeffail/benthos/lib/types"
)

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

func init() {
	Constructors[TypeCombine] = TypeSpec{
		constructor: NewCombine,
		description: `
Reads a number of discrete messages, buffering (but not acknowledging) the
message parts until the size of the batch reaches or exceeds the target size.

Once the size is reached or exceeded the parts are combined into a single batch
of messages and sent through the pipeline. After reaching a destination the
acknowledgment is sent out for all messages inside the batch at the same time,
preserving at-least-once delivery guarantees.

When a batch is sent to an output the behaviour will differ depending on the
protocol. If the output type supports multipart messages then the batch is sent
as a single message with multiple parts. If the output only supports single part
messages then the parts will be sent as a batch of single part messages. If the
output supports neither multipart or batches of messages then Benthos falls back
to sending them individually.

If a Benthos stream contains multiple brokered inputs or outputs then the batch
operator should *always* be applied directly after an input in order to avoid
unexpected behaviour and message ordering.`,
	}
}

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

// CombineConfig contains configuration fields for the Combine processor.
type CombineConfig struct {
	Parts int `json:"parts" yaml:"parts"`
}

// NewCombineConfig returns a CombineConfig with default values.
func NewCombineConfig() CombineConfig {
	return CombineConfig{
		Parts: 2,
	}
}

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

// Combine is a processor that combines messages into a batch until a target
// number of message parts is reached, at which point the batch is sent out.
// When a message is combined without yet producing a batch a NoAck response is
// returned, which is interpretted as source types as an instruction to send
// another message through but hold off on acknowledging this one.
//
// Eventually, when the batch reaches its target size, the batch is sent through
// the pipeline as a single message and an acknowledgement for that message
// determines whether the whole batch of messages are acknowledged.
type Combine struct {
	log   log.Modular
	stats metrics.Type
	n     int
	parts []types.Part

	mCount     metrics.StatCounter
	mWarnParts metrics.StatCounter
	mSent      metrics.StatCounter
	mSentParts metrics.StatCounter
	mDropped   metrics.StatCounter
}

// NewCombine returns a Combine processor.
func NewCombine(
	conf Config, mgr types.Manager, log log.Modular, stats metrics.Type,
) (Type, error) {
	return &Combine{
		log:   log.NewModule(".processor.combine"),
		stats: stats,
		n:     conf.Combine.Parts,

		mCount:     stats.GetCounter("processor.combine.count"),
		mWarnParts: stats.GetCounter("processor.combine.warning.too_many_parts"),
		mSent:      stats.GetCounter("processor.combine.sent"),
		mSentParts: stats.GetCounter("processor.combine.parts.sent"),
		mDropped:   stats.GetCounter("processor.combine.dropped"),
	}, nil
}

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

// ProcessMessage applies the processor to a message, either creating >0
// resulting messages or a response to be sent back to the message source.
func (c *Combine) ProcessMessage(msg types.Message) ([]types.Message, types.Response) {
	c.mCount.Incr(1)

	if msg.Len() > c.n {
		c.mWarnParts.Incr(1)
		c.mSent.Incr(1)
		c.mSentParts.Incr(int64(msg.Len()))
		msgs := [1]types.Message{msg}
		return msgs[:], nil
	}

	// Add new parts to the buffer.
	msg.Iter(func(i int, b types.Part) error {
		c.parts = append(c.parts, b.Copy())
		return nil
	})

	// If we have reached our target count of parts in the buffer.
	if len(c.parts) >= c.n {
		newMsg := message.New(nil)
		newMsg.Append(c.parts...)

		c.parts = nil

		c.mSent.Incr(1)
		c.mSentParts.Incr(int64(newMsg.Len()))
		c.log.Traceln("Batching based on parts")
		msgs := [1]types.Message{newMsg}
		return msgs[:], nil
	}

	c.log.Traceln("Added message to pending batch")
	c.mDropped.Incr(1)
	return nil, response.NewUnack()
}

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