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downlink_token.go
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/
downlink_token.go
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// Copyright © 2019 The Things Network Foundation, The Things Industries B.V.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package io
import (
"sync/atomic"
"time"
)
const downlinkTokenItems = 1 << 4
type downlinkToken struct {
key uint16
correlationIDs []string
time time.Time
}
// DownlinkTokens stores a set of downlink tokens and can be used to track roundtrip time.
// The number of downlink tokens stored is fixed to 16. New issued tokens with `Next` overwrite the oldest token.
type DownlinkTokens struct {
last uint32
items [downlinkTokenItems]downlinkToken
}
// Next returns a new downlink token.
func (t *DownlinkTokens) Next(correlationIDs []string, time time.Time) uint16 {
key := uint16(atomic.AddUint32(&t.last, 1))
pos := key % downlinkTokenItems
t.items[pos] = downlinkToken{
key: key,
correlationIDs: correlationIDs,
time: time,
}
return key
}
// Get returns the correlation IDs and time difference between the time given to `Next` and the given time by the token.
// If the token could not be found, this method returns false for `ok`.
func (t DownlinkTokens) Get(token uint16, time time.Time) (correlationIDs []string, delta time.Duration, ok bool) {
pos := token % downlinkTokenItems
item := t.items[pos]
if item.key != token {
return nil, 0, false
}
return item.correlationIDs, time.Sub(item.time), true
}