1 files changed, 78 insertions, 0 deletions
diff --git a/libpod/network/subnet.go b/libpod/network/subnet.go
new file mode 100644
index 000000000..90f0cdfce
--- /dev/null
+++ b/libpod/network/subnet.go
@@ -0,0 +1,78 @@
+package network
+
+/*
+	The code in this was kindly contributed by Dan Williams(dcbw@redhat.com).  Many thanks
+	for his contributions.
+*/
+
+import (
+	"fmt"
+	"net"
+)
+
+func incByte(subnet *net.IPNet, idx int, shift uint) error {
+	if idx < 0 {
+		return fmt.Errorf("no more subnets left")
+	}
+	if subnet.IP[idx] == 255 {
+		subnet.IP[idx] = 0
+		return incByte(subnet, idx-1, 0)
+	}
+	subnet.IP[idx] += 1 << shift
+	return nil
+}
+
+// NextSubnet returns subnet incremented by 1
+func NextSubnet(subnet *net.IPNet) (*net.IPNet, error) {
+	newSubnet := &net.IPNet{
+		IP:   subnet.IP,
+		Mask: subnet.Mask,
+	}
+	ones, bits := newSubnet.Mask.Size()
+	if ones == 0 {
+		return nil, fmt.Errorf("%s has only one subnet", subnet.String())
+	}
+	zeroes := uint(bits - ones)
+	shift := zeroes % 8
+	idx := ones/8 - 1
+	if idx < 0 {
+		idx = 0
+	}
+	if err := incByte(newSubnet, idx, shift); err != nil {
+		return nil, err
+	}
+	return newSubnet, nil
+}
+
+// LastIPInSubnet gets the last IP in a subnet
+func LastIPInSubnet(addr *net.IPNet) (net.IP, error) { //nolint:interfacer
+	// re-parse to ensure clean network address
+	_, cidr, err := net.ParseCIDR(addr.String())
+	if err != nil {
+		return nil, err
+	}
+
+	ones, bits := cidr.Mask.Size()
+	if ones == bits {
+		return FirstIPInSubnet(cidr)
+	}
+	hostStart := ones / 8
+	// Handle the first host byte
+	cidr.IP[hostStart] |= 0xff & cidr.Mask[hostStart]
+	// Fill the rest with ones
+	for i := hostStart; i < len(cidr.IP); i++ {
+		cidr.IP[i] = 0xff
+	}
+	return cidr.IP, nil
+}
+
+// FirstIPInSubnet gets the first IP in a subnet
+func FirstIPInSubnet(addr *net.IPNet) (net.IP, error) { //nolint:interfacer
+	// re-parse to ensure clean network address
+	_, cidr, err := net.ParseCIDR(addr.String())
+	if err != nil {
+		return nil, err
+	}
+	cidr.IP[len(cidr.IP)-1]++
+	return cidr.IP, nil
+}