fan_out.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/benthos/lib/util/service/log"
	"github.com/Jeffail/benthos/lib/util/service/metrics"
)

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

var (
	// ErrFanOutNoOutputs is returned when creating a FanOut type with zero
	// outputs.
	ErrFanOutNoOutputs = errors.New("attempting to create fan_out output type with no outputs")
)

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

func init() {
	constructors["fan_out"] = typeSpec{
		constructor: NewFanOut,
		description: `
The fan out output type allows you to configure multiple output targets. With
the fan out model all outputs will be sent every message that passes through
benthos.

This process is blocking, meaning if any output applies backpressure then it
will block all outputs from receiving messages. If an output fails to guarantee
receipt of a message it will be tried again until success.

If Benthos is stopped during a fan out send it is possible that when started
again it will send a duplicate message to some outputs.`,
	}
}

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

// FanOutConfig is configuration for the FanOut output type.
type FanOutConfig struct {
	Outputs []interface{} `json:"outputs" yaml:"outputs"`
}

// NewFanOutConfig creates a new FanOutConfig with default values.
func NewFanOutConfig() FanOutConfig {
	return FanOutConfig{
		Outputs: []interface{}{},
	}
}

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

// NewFanOut creates a new FanOut output type. Messages will be sent out to ALL
// outputs, outputs which block will apply backpressure upstream, meaning other
// outputs will also stop receiving messages.
func NewFanOut(conf Config, mgr types.Manager, log log.Modular, stats metrics.Type) (Type, error) {
	if len(conf.FanOut.Outputs) == 0 {
		return nil, ErrFanOutNoOutputs
	}

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

	if len(outputConfs) == 0 {
		return nil, ErrFanOutNoOutputs
	} else if len(outputConfs) == 1 {
		return New(outputConfs[0], mgr, log, stats)
	}

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

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

	return broker.NewFanOut(broker.NewFanOutConfig(), outputs, log, stats)
}

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