round_robin.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 output

import (
	"errors"

	"github.com/jeffail/benthos/lib/broker"
	"github.com/jeffail/benthos/lib/types"
	"github.com/jeffail/util/log"
	"github.com/jeffail/util/metrics"
)

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

var (
	// ErrRoundRobinNoOutputs - Returned when creating a RoundRobin type with zero outputs.
	ErrRoundRobinNoOutputs = errors.New("attempting to create round_robin output with no outputs")
)

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

func init() {
	constructors["round_robin"] = typeSpec{
		constructor: NewRoundRobin,
		description: `
The 'round_robin' output type allows you to send messages across multiple
outputs, where each message is sent to exactly one output following a strict
order.

If an output applies back pressure this will also block other outputs from
receiving content.`,
	}
}

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

// RoundRobinConfig - Configuration for the RoundRobin output type.
type RoundRobinConfig struct {
	Outputs []interface{} `json:"outputs" yaml:"outputs"`
}

// NewRoundRobinConfig - Creates a new RoundRobinConfig with default values.
func NewRoundRobinConfig() RoundRobinConfig {
	return RoundRobinConfig{
		Outputs: []interface{}{},
	}
}

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

// NewRoundRobin - Create a new RoundRobin output type. Messages will be sent out to an output
// chosen by following their original order. If an output blocks this will block all throughput.
func NewRoundRobin(conf Config, log log.Modular, stats metrics.Type) (Type, error) {
	if len(conf.RoundRobin.Outputs) == 0 {
		return nil, ErrRoundRobinNoOutputs
	}

	outputConfs, err := parseOutputConfsWithDefaults(conf.RoundRobin.Outputs)
	if err != nil {
		return nil, err
	}

	outputs := make([]types.Consumer, len(outputConfs))

	for i, oConf := range outputConfs {
		outputs[i], err = New(oConf, log, stats)
		if err != nil {
			return nil, err
		}
	}

	return broker.NewRoundRobin(outputs, stats)
}

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