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// Copyright (C) 2019-2023 Algorand, Inc.
// This file is part of go-algorand
//
// go-algorand is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as
// published by the Free Software Foundation, either version 3 of the
// License, or (at your option) any later version.
//
// go-algorand is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with go-algorand. If not, see <https://www.gnu.org/licenses/>.
package dnssec
import (
"math/rand"
"net"
"sort"
)
type srvRecArray []*net.SRV
func (a srvRecArray) Len() int {
return len(a)
}
func (a srvRecArray) Less(i, j int) bool {
return a[i].Priority < a[j].Priority || a[i].Priority == a[j].Priority && a[i].Weight < a[j].Weight
}
func (a srvRecArray) Swap(i, j int) {
a[i], a[j] = a[j], a[i]
}
// randomize SRV records by weight within the same priority with indices [start, end)
// https://tools.ietf.org/html/rfc2782
func (a srvRecArray) randomize(start, end int) {
// Compute the sum of the weights of those RRs
sum := 0
for i := start; i < end; i++ {
sum += int(a[i].Weight)
}
for sum > 0 && end-start > 0 {
// Then choose a uniform random number between 0 and the sum computed (inclusive)
num := rand.Intn(sum + 1)
// And select the RR whose running sum value is the first in the selected order
// which is greater than or equal to the random number selected.
rSum := 0
for i := start; i < end; i++ {
rSum += int(a[i].Weight)
if rSum >= num {
// Remove this SRV RR from the set of the unordered SRV RRs
a[start], a[i] = a[i], a[start]
break
}
}
// And apply the described algorithm to the unordered SRV RRs to select the next target host.
sum -= int(a[start].Weight)
start++
}
}
func (a srvRecArray) sortAndRand() {
sort.Sort(a)
i := 0
for j := 1; j < len(a); j++ {
if a[i].Priority != a[j].Priority {
a.randomize(i, j)
i = j
}
}
a.randomize(i, len(a))
}
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