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preserver.go
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preserver.go
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// Copyright (c) 2018 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 reader
import (
"time"
"github.com/Jeffail/benthos/lib/types"
"github.com/Jeffail/benthos/lib/util/throttle"
)
//------------------------------------------------------------------------------
// Preserver is a wrapper for reader.Type implementations that keeps a buffer of
// sent messages until they are acknowledged. If an error occurs during message
// propagation the contents of the buffer will be resent instead of reading new
// messages until it is depleted. Preserver implements reader.Type.
type Preserver struct {
unAckMessages []types.Message
resendMessages []types.Message
throt *throttle.Type
r Type
}
// NewPreserver returns a new Preserver wrapper around a reader.Type.
func NewPreserver(r Type) *Preserver {
return &Preserver{
r: r,
throt: throttle.New(
throttle.OptThrottlePeriod(time.Second),
),
}
}
//------------------------------------------------------------------------------
// Connect attempts to establish a connection to the source, if unsuccessful
// returns an error. If the attempt is successful (or not necessary) returns
// nil.
func (p *Preserver) Connect() error {
return p.r.Connect()
}
// Acknowledge instructs whether messages read since the last Acknowledge call
// were successfully propagated. If the error is nil this will be forwarded to
// the underlying wrapped reader. If a non-nil error is returned the buffer of
// messages will be resent.
func (p *Preserver) Acknowledge(err error) error {
if err == nil {
p.throt.Reset()
p.unAckMessages = nil
if len(p.resendMessages) == 0 {
// Only propagate ack if we are done resending buffered messages.
return p.r.Acknowledge(err)
}
return nil
}
// Do not propagate errors since we are handling them here by resending.
p.resendMessages = append(p.resendMessages, p.unAckMessages...)
p.unAckMessages = nil
p.throt.Retry()
return nil
}
// Read attempts to read a new message from the source.
func (p *Preserver) Read() (types.Message, error) {
// If we have messages queued to be resent we prioritise them over reading
// new messages.
if lMsgs := len(p.resendMessages); lMsgs > 0 {
msg := p.resendMessages[0]
if lMsgs > 1 {
p.resendMessages = p.resendMessages[1:]
} else {
p.resendMessages = nil
}
p.unAckMessages = append(p.unAckMessages, msg)
return msg, nil
}
msg, err := p.r.Read()
if err == nil {
p.unAckMessages = append(p.unAckMessages, msg)
}
return msg, err
}
// CloseAsync triggers the asynchronous closing of the reader.
func (p *Preserver) CloseAsync() {
p.r.CloseAsync()
}
// WaitForClose blocks until either the reader is finished closing or a timeout
// occurs.
func (p *Preserver) WaitForClose(tout time.Duration) error {
return p.r.WaitForClose(tout)
}
//------------------------------------------------------------------------------