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subnet_allocator.go
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subnet_allocator.go
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package netutils
import (
"fmt"
"net"
)
type SubnetAllocator struct {
network *net.IPNet
hostBits uint32
leftShift uint32
leftMask uint32
rightShift uint32
rightMask uint32
next uint32
allocMap map[string]bool
}
func NewSubnetAllocator(network string, hostBits uint32, inUse []string) (*SubnetAllocator, error) {
_, netIP, err := net.ParseCIDR(network)
if err != nil {
return nil, fmt.Errorf("Failed to parse network address: %q", network)
}
netMaskSize, _ := netIP.Mask.Size()
if hostBits > (32 - uint32(netMaskSize)) {
return nil, fmt.Errorf("Subnet capacity cannot be larger than number of networks available.")
}
subnetBits := 32 - uint32(netMaskSize) - hostBits
// In the simple case, the subnet part of the 32-bit IP address is just the subnet
// number shifted hostBits to the left. However, if hostBits isn't a multiple of
// 8, then it can be difficult to distinguish the subnet part and the host part
// visually. (Eg, given network="10.1.0.0/16" and hostBits=6, then "10.1.0.50" and
// "10.1.0.70" are on different networks.)
//
// To try to avoid this confusion, if the subnet extends into the next higher
// octet, we rotate the bits of the subnet number so that we use the subnets with
// all 0s in the shared octet first. So again given network="10.1.0.0/16",
// hostBits=6, we first allocate 10.1.0.0/26, 10.1.1.0/26, etc, through
// 10.1.255.0/26 (just like we would with /24s in the hostBits=8 case), and only
// if we use up all of those subnets do we start allocating 10.1.0.64/26,
// 10.1.1.64/26, etc.
var leftShift, rightShift uint32
var leftMask, rightMask uint32
if hostBits%8 != 0 && ((hostBits-1)/8 != (hostBits+subnetBits-1)/8) {
leftShift = 8 - (hostBits % 8)
leftMask = uint32(1)<<(32-uint32(netMaskSize)) - 1
rightShift = subnetBits - leftShift
rightMask = (uint32(1)<<leftShift - 1) << hostBits
} else {
leftShift = 0
leftMask = 0xFFFFFFFF
rightShift = 0
rightMask = 0
}
amap := make(map[string]bool)
for _, netStr := range inUse {
_, nIp, err := net.ParseCIDR(netStr)
if err != nil {
fmt.Println("Failed to parse network address: ", netStr)
continue
}
if !netIP.Contains(nIp.IP) {
fmt.Println("Provided subnet doesn't belong to network: ", nIp)
continue
}
amap[nIp.String()] = true
}
return &SubnetAllocator{
network: netIP,
hostBits: hostBits,
leftShift: leftShift,
leftMask: leftMask,
rightShift: rightShift,
rightMask: rightMask,
next: 0,
allocMap: amap,
}, nil
}
func (sna *SubnetAllocator) GetNetwork() (*net.IPNet, error) {
var (
numSubnets uint32
numSubnetBits uint32
)
baseipu := IPToUint32(sna.network.IP)
netMaskSize, _ := sna.network.Mask.Size()
numSubnetBits = 32 - uint32(netMaskSize) - sna.hostBits
numSubnets = 1 << numSubnetBits
var i uint32
for i = 0; i < numSubnets; i++ {
n := (i + sna.next) % numSubnets
shifted := n << sna.hostBits
ipu := baseipu | ((shifted << sna.leftShift) & sna.leftMask) | ((shifted >> sna.rightShift) & sna.rightMask)
genIp := Uint32ToIP(ipu)
genSubnet := &net.IPNet{IP: genIp, Mask: net.CIDRMask(int(numSubnetBits)+netMaskSize, 32)}
if !sna.allocMap[genSubnet.String()] {
sna.allocMap[genSubnet.String()] = true
sna.next = n + 1
return genSubnet, nil
}
}
sna.next = 0
return nil, fmt.Errorf("No subnets available.")
}
func (sna *SubnetAllocator) ReleaseNetwork(ipnet *net.IPNet) error {
if !sna.network.Contains(ipnet.IP) {
return fmt.Errorf("Provided subnet %v doesn't belong to the network %v.", ipnet, sna.network)
}
ipnetStr := ipnet.String()
if !sna.allocMap[ipnetStr] {
return fmt.Errorf("Provided subnet %v is already available.", ipnet)
}
sna.allocMap[ipnetStr] = false
return nil
}