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subnet.go
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subnet.go
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/*
* Copyright 2018-2023, CS Systemes d'Information, http://csgroup.eu
*
* 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 net
import (
"net"
"github.com/CS-SI/SafeScale/v22/lib/utils/fail"
)
// FirstIncludedSubnet takes a parent CIDR range and gives the first subnet within it
// with the given number of additional prefix bits 'maskAddition'.
//
// For example, 192.168.0.0/16, extended by 8 bits becomes 192.168.0.0/24.
func FirstIncludedSubnet(base net.IPNet, maskAddition uint8) (net.IPNet, fail.Error) {
return NthIncludedSubnet(base, maskAddition, 0)
}
// NthIncludedSubnet takes a parent CIDR range and gives the 'nth' subnet within it with the
// given numver of additional prefix bits 'maskAddition'
//
// For example, 192.168.0.0/16, extended by 8 bits gives as 4th subnet 192.168.4.0/24.
func NthIncludedSubnet(base net.IPNet, maskAddition uint8, nth uint) (net.IPNet, fail.Error) {
ip := base.IP
mask := base.Mask
parentLen, addrLen := mask.Size()
newPrefixLen := parentLen + int(maskAddition)
if newPrefixLen > addrLen {
return net.IPNet{}, fail.OverflowError(nil, uint(addrLen), "insufficient address space to extend prefix of %d by %d", parentLen, maskAddition)
}
var maxNetNum uint64 = 1<<maskAddition - 1
if uint64(1) > maxNetNum {
return net.IPNet{}, fail.OverflowError(nil, uint(maxNetNum), "prefix extension of %d does not accommodate a subnet", maskAddition)
}
ipAsNumber := IPv4ToUInt32(ip)
bitShift := uint32(32 - newPrefixLen)
ipAsNumber |= uint32(nth) << bitShift
return net.IPNet{
IP: UInt32ToIPv4(ipAsNumber),
Mask: net.CIDRMask(newPrefixLen, addrLen),
}, nil
}