// Copyright (c) 2016-2021 Tigera, Inc. All rights reserved.
//
// 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 ipam

import (
	"context"
	"errors"
	"fmt"
	"math/bits"
	"runtime"
	"strings"
	"time"

	log "github.com/sirupsen/logrus"
	"golang.org/x/sync/semaphore"

	v3 "github.com/projectcalico/api/pkg/apis/projectcalico/v3"

	libapiv3 "github.com/projectcalico/calico/libcalico-go/lib/apis/v3"
	bapi "github.com/projectcalico/calico/libcalico-go/lib/backend/api"
	"github.com/projectcalico/calico/libcalico-go/lib/backend/model"
	cerrors "github.com/projectcalico/calico/libcalico-go/lib/errors"
	"github.com/projectcalico/calico/libcalico-go/lib/names"
	"github.com/projectcalico/calico/libcalico-go/lib/net"
	"github.com/projectcalico/calico/libcalico-go/lib/options"
	"github.com/projectcalico/calico/libcalico-go/lib/set"
)

const (
	// Number of retries when we have an error writing data
	// to etcd.
	datastoreRetries  = 100
	ipamKeyErrRetries = 3

	// Common attributes which may be set on allocations by clients.  Moved to the model package so they can be used
	// by the AllocationBlock code too.
	AttributePod             = model.IPAMBlockAttributePod
	AttributeNamespace       = model.IPAMBlockAttributeNamespace
	AttributeNode            = model.IPAMBlockAttributeNode
	AttributeTimestamp       = model.IPAMBlockAttributeTimestamp
	AttributeType            = model.IPAMBlockAttributeType
	AttributeTypeIPIP        = model.IPAMBlockAttributeTypeIPIP
	AttributeTypeVXLAN       = model.IPAMBlockAttributeTypeVXLAN
	AttributeTypeVXLANV6     = model.IPAMBlockAttributeTypeVXLANV6
	AttributeTypeWireguard   = model.IPAMBlockAttributeTypeWireguard
	AttributeTypeWireguardV6 = model.IPAMBlockAttributeTypeWireguardV6
)

var (
	ErrBlockLimit      = errors.New("cannot allocate new block due to per host block limit")
	ErrNoQualifiedPool = errors.New("cannot find a qualified ippool")
	ErrStrictAffinity  = errors.New("global strict affinity should not be false for Windows node")
)

// IPReservationInterface is the subset of clientv3.IPReservationInterface that we need.
type IPReservationInterface interface {
	List(ctx context.Context, opts options.ListOptions) (*v3.IPReservationList, error)
}

// NewIPAMClient returns a new ipamClient, which implements Interface.
// Consumers of the Calico API should not create this directly, but should
// access IPAM through the main client IPAM accessor (e.g. clientv3.IPAM())
func NewIPAMClient(client bapi.Client, pools PoolAccessorInterface, reservations IPReservationInterface) Interface {
	return &ipamClient{
		client:       client,
		pools:        pools,
		reservations: reservations,
		blockReaderWriter: blockReaderWriter{
			client: client,
			pools:  pools,
		},
	}
}

// ipamClient implements Interface
type ipamClient struct {
	client            bapi.Client
	pools             PoolAccessorInterface
	blockReaderWriter blockReaderWriter
	reservations      IPReservationInterface
}

// AutoAssign automatically assigns one or more IP addresses as specified by the
// provided AutoAssignArgs.  AutoAssign returns the list of the assigned IPv4 addresses,
// and the list of the assigned IPv6 addresses.
//
// In case of error, returns the IPs allocated so far along with the error.
func (c ipamClient) AutoAssign(ctx context.Context, args AutoAssignArgs) (*IPAMAssignments, *IPAMAssignments, error) {
	// Determine the hostname to use - prefer the provided hostname if
	// non-nil, otherwise use the hostname reported by os.
	hostname, err := decideHostname(args.Hostname)
	if err != nil {
		return nil, nil, err
	}
	log.Infof("Auto-assign %d ipv4, %d ipv6 addrs for host '%s'", args.Num4, args.Num6, hostname)

	var v4ia, v6ia *IPAMAssignments

	if args.Num4 != 0 {
		// Assign IPv4 addresses.
		log.Debugf("Assigning IPv4 addresses")
		for _, pool := range args.IPv4Pools {
			if pool.IP.To4() == nil {
				return nil, nil, fmt.Errorf("provided IPv4 IPPools list contains one or more IPv6 IPPools")
			}
		}
		v4ia, err = c.autoAssign(ctx, args.Num4, args.HandleID, args.Attrs, args.IPv4Pools, 4, hostname, args.MaxBlocksPerHost, args.HostReservedAttrIPv4s, args.IntendedUse)
		if err != nil {
			log.Errorf("Error assigning IPV4 addresses: %v", err)
			return v4ia, nil, err
		}
	}

	if args.Num6 != 0 {
		// If no err assigning V4, try to assign any V6.
		log.Debugf("Assigning IPv6 addresses")
		for _, pool := range args.IPv6Pools {
			if pool.IP.To4() != nil {
				return nil, nil, fmt.Errorf("provided IPv6 IPPools list contains one or more IPv4 IPPools")
			}
		}
		v6ia, err = c.autoAssign(ctx, args.Num6, args.HandleID, args.Attrs, args.IPv6Pools, 6, hostname, args.MaxBlocksPerHost, args.HostReservedAttrIPv6s, args.IntendedUse)
		if err != nil {
			log.Errorf("Error assigning IPV6 addresses: %v", err)
			return v4ia, v6ia, err
		}
	}

	return v4ia, v6ia, nil
}

// getBlockFromAffinity returns the block referenced by the given affinity, attempting to create it if
// it does not exist. getBlockFromAffinity will delete the provided affinity if it does not match the actual
// affinity of the block.
func (c ipamClient) getBlockFromAffinity(ctx context.Context, aff *model.KVPair, rsvdAttr *HostReservedAttr) (*model.KVPair, error) {
	// Parse out affinity data.
	cidr := aff.Key.(model.BlockAffinityKey).CIDR
	host := aff.Key.(model.BlockAffinityKey).Host
	state := aff.Value.(*model.BlockAffinity).State
	logCtx := log.WithFields(log.Fields{"host": host, "cidr": cidr})

	// Get the block referenced by this affinity.
	logCtx.Info("Attempting to load block")
	b, err := c.blockReaderWriter.queryBlock(ctx, cidr, "")
	if err != nil {
		if _, ok := err.(cerrors.ErrorResourceDoesNotExist); ok {
			// The block referenced by the affinity doesn't exist. Try to create it.
			logCtx.Info("The referenced block doesn't exist, trying to create it")
			aff.Value.(*model.BlockAffinity).State = model.StatePending
			aff, err = c.blockReaderWriter.updateAffinity(ctx, aff)
			if err != nil {
				logCtx.WithError(err).Warn("Error updating block affinity")
				return nil, err
			}
			logCtx.Info("Wrote affinity as pending")

			cfg, err := c.GetIPAMConfig(ctx)
			if err != nil {
				logCtx.WithError(err).Errorf("Error getting IPAM Config")
				return nil, err
			}

			// Claim the block, which will also confirm the affinity.
			logCtx.Info("Attempting to claim the block")
			b, err := c.blockReaderWriter.claimAffineBlock(ctx, aff, *cfg, rsvdAttr)
			if err != nil {
				logCtx.WithError(err).Warn("Error claiming block")
				return nil, err
			}
			return b, nil
		}
		logCtx.WithError(err).Error("Error getting block")
		return nil, err
	}

	// If the block doesn't match the affinity, it means we've got a stale affinity hanging around.
	// We should remove it.
	blockAffinity := b.Value.(*model.AllocationBlock).Affinity
	if blockAffinity == nil || *blockAffinity != fmt.Sprintf("host:%s", host) {
		logCtx.WithField("blockAffinity", blockAffinity).Warn("Block does not match the provided affinity, deleting stale affinity")
		err := c.blockReaderWriter.deleteAffinity(ctx, aff)
		if err != nil {
			logCtx.WithError(err).Warn("Error deleting stale affinity")
			return nil, err
		}
		return nil, errStaleAffinity(fmt.Sprintf("Affinity is stale: %+v", aff))
	}

	// If the block does match the affinity but the affinity has not been confirmed,
	// try to confirm it. Treat empty string as confirmed for compatibility with older data.
	if state != model.StateConfirmed && state != "" {
		// Write the affinity as pending.
		logCtx.Info("Affinity has not been confirmed - attempt to confirm it")
		aff.Value.(*model.BlockAffinity).State = model.StatePending
		aff, err = c.blockReaderWriter.updateAffinity(ctx, aff)
		if err != nil {
			logCtx.WithError(err).Warn("Error marking affinity as pending as part of confirmation process")
			return nil, err
		}

		// CAS the block to get a new revision and invalidate any other instances
		// that might be trying to operate on the block.
		logCtx.Info("Writing block to get a new revision")
		b, err = c.blockReaderWriter.updateBlock(ctx, b)
		if err != nil {
			logCtx.WithError(err).Debug("Error writing block")
			return nil, err
		}

		// Confirm the affinity.
		logCtx.Info("Attempting to confirm affinity")
		aff.Value.(*model.BlockAffinity).State = model.StateConfirmed
		aff, err = c.blockReaderWriter.updateAffinity(ctx, aff)
		if err != nil {
			logCtx.WithError(err).Debug("Error confirming affinity")
			return nil, err
		}
		logCtx.Info("Affinity confirmed successfully")
	}
	logCtx.Info("Affinity is confirmed and block has been loaded")
	return b, nil
}

// function to check if context has associated OS parameter
// fallback to GOOS in other case
func detectOS(ctx context.Context) string {
	if osOverride := ctx.Value("windowsHost"); osOverride != nil {
		return osOverride.(string)
	}
	return runtime.GOOS
}

// determinePools compares a list of requested pools with the enabled pools and returns the intersect.
// If any requested pool does not exist, or is not enabled, an error is returned.
// If no pools are requested, all enabled pools are returned.
// Also applies selector logic on node labels to determine if the pool is a match.
// Returns the set of matching pools as well as the full set of ip pools.
func (c ipamClient) determinePools(ctx context.Context, requestedPoolNets []net.IPNet, version int, node libapiv3.Node, maxPrefixLen int) (matchingPools, enabledPools []v3.IPPool, err error) {
	// Get all the enabled IP pools from the datastore.
	enabledPools, err = c.pools.GetEnabledPools(version)
	if err != nil {
		log.WithError(err).Errorf("Error getting IP pools")
		return
	}
	log.Debugf("enabled pools: %v", enabledPools)
	log.Debugf("requested pools: %v", requestedPoolNets)

	// Build a map so we can lookup existing pools.
	pm := map[string]v3.IPPool{}

	var cidr *net.IPNet
	for _, p := range enabledPools {
		if p.Spec.BlockSize > maxPrefixLen {
			log.Warningf("skipping pool %v due to blockSize %d bigger than %d", p, p.Spec.BlockSize, maxPrefixLen)
			continue
		}
		_, cidr, err = net.ParseCIDR(p.Spec.CIDR)
		if err != nil {
			log.WithError(err).Errorf("Pool %s has invalid CIDR %s", p.Name, p.Spec.CIDR)
			return
		}
		pm[cidr.String()] = p
	}

	if len(pm) == 0 {
		// None of the enabled pools are qualified.
		err = ErrNoQualifiedPool
		return
	}

	// Build a list of requested IP pool objects based on the provided CIDRs, validating
	// that each one actually exists and is enabled for IPAM.
	requestedPools := []v3.IPPool{}
	for _, rp := range requestedPoolNets {
		cidr := rp.Network()
		if pool, ok := pm[cidr.String()]; !ok {
			// The requested pool doesn't exist.
			err = fmt.Errorf("the given pool (%s) does not exist, or is not enabled", cidr.String())
			return
		} else {
			requestedPools = append(requestedPools, pool)
		}
	}

	// If requested IP pools are provided, use those unconditionally. We will ignore
	// IP pool selectors in this case. We need this for backwards compatibility, since IP pool
	// node selectors have not always existed.
	if len(requestedPools) > 0 {
		log.Debugf("Using the requested IP pools")
		matchingPools = requestedPools
		return
	}

	// At this point, we've determined the set of enabled IP pools which are valid for use.
	// We only want to use IP pools which actually match this node, so do a filter based on
	// selector.
	for _, pool := range enabledPools {
		var matches bool
		matches, err = SelectsNode(pool, node)
		if err != nil {
			log.WithError(err).WithField("pool", pool).Error("failed to determine if node matches pool")
			return
		}
		if !matches {
			// Do not consider pool enabled if the nodeSelector doesn't match the node's labels.
			log.Debugf("IP pool does not match this node: %s", pool.Name)
			continue
		}
		log.Debugf("IP pool matches this node: %s", pool.Name)
		matchingPools = append(matchingPools, pool)
	}

	return
}

// prepareAffinityBlocksForHost returns a list of blocks affine to a node based on requested IP pools.
// It also releases any emptied blocks still affine to this host but no longer part of an IP Pool which
// selects this node. It returns matching pools, list of host-affine blocks and any error encountered.
func (c ipamClient) prepareAffinityBlocksForHost(ctx context.Context, requestedPools []net.IPNet, version int, host string, rsvdAttr *HostReservedAttr, use v3.IPPoolAllowedUse) ([]v3.IPPool, []net.IPNet, error) {
	// Retrieve node for given hostname to use for ip pool node selection
	node, err := c.client.Get(ctx, model.ResourceKey{Kind: libapiv3.KindNode, Name: host}, "")
	if err != nil {
		log.WithError(err).WithField("node", host).Error("failed to get node for host")
		return nil, nil, err
	}

	// Make sure the returned value is OK.
	v3n, ok := node.Value.(*libapiv3.Node)
	if !ok {
		return nil, nil, fmt.Errorf("Datastore returned malformed node object")
	}

	maxPrefixLen, err := getMaxPrefixLen(version, rsvdAttr)
	if err != nil {
		return nil, nil, err
	}

	// Determine the correct set of IP pools to use for this request.
	poolsSelectingNode, allPools, err := c.determinePools(ctx, requestedPools, version, *v3n, maxPrefixLen)
	if err != nil {
		return nil, nil, err
	}
	if len(poolsSelectingNode) == 0 {
		return nil, nil, fmt.Errorf("no configured Calico pools for node %s", host)
	}

	// Figure out what subset of the selecting pools we're allowed to use for the request according to the
	// pool's allowed use.
	poolsAllowedByUse := filterPoolsByUse(poolsSelectingNode, use)
	log.Debugf("Pools filtered by allowed use: %v", poolsAllowedByUse)

	// If there are no allowed pools, we cannot assign addresses.
	if len(poolsAllowedByUse) == 0 {
		return nil, nil, fmt.Errorf("%w, no pools match the required use (%v)", ErrNoQualifiedPool, use)
	}

	logCtx := log.WithFields(log.Fields{"host": host})

	// Look for any existing affine blocks.
	logCtx.Info("Looking up existing affinities for host")
	allAffBlocks, err := c.blockReaderWriter.getAffineBlocks(ctx, host, version)
	if err != nil {
		return nil, nil, err
	}

	// Split the blocks into ones that we're allowed to use and ones that we're not allowed to use for this
	// allocation.
	allowedAffBlocks, nonAllowedAffBlocks, err := filterBlocksByPools(allAffBlocks, poolsAllowedByUse)
	if err != nil {
		return nil, nil, err
	}
	// Further, split the non-allowed blocks into ones that are from pools that select this node and pools that
	// don't select this node.  We'll try to release the latter below.
	_, affBlocksToRelease, err := filterBlocksByPools(nonAllowedAffBlocks, poolsSelectingNode)
	if err != nil {
		return nil, nil, err
	}

	// Release any emptied blocks still affine to this host but no longer part of an IP Pool which selects this node.
	for _, block := range affBlocksToRelease {
		// Determine the pool for each block.
		pool, err := c.blockReaderWriter.getPoolForIP(net.IP{IP: block.IP}, allPools)
		if err != nil {
			log.WithError(err).Warnf("Failed to get pool for IP")
			continue
		}
		if pool == nil {
			logCtx.WithFields(log.Fields{"block": block}).Warn("No pool found for block, skipping")
			continue
		}

		// Determine if the pool selects the current node, refusing to release this particular block affinity if so.
		blockSelectsNode, err := SelectsNode(*pool, *v3n)
		if err != nil {
			logCtx.WithError(err).WithField("pool", pool).Error("Failed to determine if node matches pool, skipping")
			continue
		}
		if blockSelectsNode {
			logCtx.WithFields(log.Fields{"pool": pool, "block": block}).Debug("Block's pool still selects node, refusing to remove affinity")
			continue
		}

		// Release the block affinity, requiring it to be empty.
		for i := 0; i < datastoreRetries; i++ {
			if err = c.blockReaderWriter.releaseBlockAffinity(ctx, host, block, true); err != nil {
				if _, ok := err.(errBlockClaimConflict); ok {
					// Not claimed by this host - ignore.
				} else if _, ok := err.(errBlockNotEmpty); ok {
					// Block isn't empty - ignore.
				} else if _, ok := err.(cerrors.ErrorResourceDoesNotExist); ok {
					// Block does not exist - ignore.
				} else {
					logCtx.WithError(err).WithField("block", block).Warn("Error occurred releasing block, trying again")
					continue
				}
			}
			logCtx.WithField("block", block).Info("Released affine block that no longer selects this host")
			break
		}
	}

	return poolsAllowedByUse, allowedAffBlocks, nil
}

// filterPoolsByUse returns a slice containing the subset of the input pools that are allowed for the given use.
// Handles defaulting of the allowed uses if not specified on the pool.
func filterPoolsByUse(pools []v3.IPPool, use v3.IPPoolAllowedUse) []v3.IPPool {
	var filteredPools []v3.IPPool
	for _, p := range pools {
		for _, allowed := range p.Spec.AllowedUses {
			if allowed == use {
				filteredPools = append(filteredPools, p)
				break
			}
		}
	}
	return filteredPools
}

// blockAssignState manages the state in relation to the request of finding or claiming a block for a host.
type blockAssignState struct {
	client                ipamClient
	version               int
	host                  string
	pools                 []v3.IPPool
	remainingAffineBlocks []net.IPNet
	hostReservedAttr      *HostReservedAttr
	allowNewClaim         bool
	reservations          addrFilter

	// For UT purpose, how many times datastore retry has been triggered.
	datastoreRetryCount int
}

// Given a list of host-affine blocks, findOrClaimBlock returns one block with minimum free ips.
// It tries to use one of the current host-affine blocks first and if not found, it will claim a new block
// and assign affinity.
// It returns a block, a boolean if block is newly claimed and any error encountered.
func (s *blockAssignState) findOrClaimBlock(ctx context.Context, minFreeIps int) (*model.KVPair, bool, error) {
	logCtx := log.WithFields(log.Fields{"host": s.host})

	// First, we try to find a block from one of the existing host-affine blocks.
	for len(s.remainingAffineBlocks) > 0 {
		// Pop first cidr.
		cidr := s.remainingAffineBlocks[0]
		s.remainingAffineBlocks = s.remainingAffineBlocks[1:]

		if s.reservations.MatchesWholeCIDR(&cidr) {
			log.WithField("cidr", cidr).Debug("Ignoring block, it is entirely reserved.")
			continue
		}

		// Checking this block - if we hit a CAS error, we'll try this block again.
		// For any other error, we'll break out and try the next affine block.
		for i := 0; i < datastoreRetries; i++ {
			// Get the affinity.
			logCtx.Infof("Trying affinity for %s", cidr)
			aff, err := s.client.blockReaderWriter.queryAffinity(ctx, s.host, cidr, "")
			if err != nil {
				logCtx.WithError(err).Warnf("Error getting affinity")
				break
			}

			// Get the block which is referenced by the affinity, creating it if necessary.
			b, err := s.client.getBlockFromAffinity(ctx, aff, s.hostReservedAttr)
			if err != nil {
				// Couldn't get a block for this affinity.
				if _, ok := err.(cerrors.ErrorResourceUpdateConflict); ok {
					logCtx.WithError(err).Debug("CAS error getting affine block - retry")
					continue
				}
				logCtx.WithError(err).Warn("Couldn't get block for affinity, try next one")
				break
			}

			// Pull out the block.
			block := allocationBlock{b.Value.(*model.AllocationBlock)}
			numFreeAddresses := block.NumFreeAddresses(s.reservations)
			if numFreeAddresses >= minFreeIps {
				logCtx.Debugf("Block '%s' has %d free ips which is more than %d ips required.", cidr.String(), numFreeAddresses, minFreeIps)
				return b, false, nil
			} else {
				logCtx.Debugf("Block '%s' has %d free ips which is less than %d ips required.", cidr.String(), numFreeAddresses, minFreeIps)
				break
			}
		}
	}

	logCtx.Infof("Ran out of existing affine blocks for host")

	if !s.allowNewClaim {
		return nil, false, ErrBlockLimit
	}

	// Find unclaimed block if AutoAllocateBlocks is true.
	config, err := s.client.GetIPAMConfig(ctx)
	if err != nil {
		return nil, false, err
	}
	logCtx.Debugf("Allocate new blocks? Config: %+v", config)
	if config.AutoAllocateBlocks {
		for i := 0; i < datastoreRetries; i++ {
			// First, try to find a usable block. findUsableBlock will usually return a new block, or in rare scenarios an already
			// allocated affine block. This may happen due to a race condition where another process on the host allocates a new block
			// after we decide that a new block is required to satisfy this request, but before we actually allocate a new block.
			logCtx.Info("Tried all affine blocks. Looking for an affine block with space, or a new unclaimed block")
			subnet, err := s.client.blockReaderWriter.findUsableBlock(ctx, s.host, s.version, s.pools, s.reservations, *config)
			if err != nil {
				if _, ok := err.(noFreeBlocksError); ok {
					// No free blocks.  Break.
					logCtx.Info("No free blocks available for allocation")
				} else {
					log.WithError(err).Error("Failed to find an unclaimed block")
				}
				return nil, false, err
			}
			logCtx := log.WithFields(log.Fields{"host": s.host, "subnet": subnet})
			logCtx.Info("Found unclaimed block")

			for j := 0; j < datastoreRetries; j++ {
				// We found an unclaimed block - claim affinity for it.
				pa, err := s.client.blockReaderWriter.getPendingAffinity(ctx, s.host, *subnet)
				if err != nil {
					if _, ok := err.(cerrors.ErrorResourceUpdateConflict); ok {
						logCtx.WithError(err).Debug("CAS error claiming pending affinity, retry")
						continue
					}
					logCtx.WithError(err).Errorf("Error claiming pending affinity")
					return nil, false, err
				}

				// We have an affinity - try to get the block.
				b, err := s.client.getBlockFromAffinity(ctx, pa, s.hostReservedAttr)
				if err != nil {
					if _, ok := err.(cerrors.ErrorResourceUpdateConflict); ok {
						logCtx.WithError(err).Debug("CAS error getting block, retry")
						continue
					} else if _, ok := err.(errBlockClaimConflict); ok {
						logCtx.WithError(err).Debug("Block taken by someone else, find a new one")
						break
					} else if _, ok := err.(errStaleAffinity); ok {
						logCtx.WithError(err).Debug("Affinity is stale, find a new one")
						break
					}
					logCtx.WithError(err).Errorf("Error getting block for affinity")
					return nil, false, err
				}

				// Claim successful.
				block := allocationBlock{b.Value.(*model.AllocationBlock)}
				numFree := block.NumFreeAddresses(s.reservations)
				if numFree >= minFreeIps {
					logCtx.Infof("Block '%s' has %d free ips which is more than %d ips required.",
						b.Key.(model.BlockKey).CIDR, numFree, minFreeIps)
					return b, true, nil
				} else {
					errString := fmt.Sprintf("Block '%s' has %d free ips which is less than %d ips required.",
						b.Key.(model.BlockKey).CIDR, numFree, minFreeIps)
					logCtx.Errorf(errString)
					return nil, false, errors.New(errString)
				}
			}
			s.datastoreRetryCount++
		}
		return nil, false, errors.New("Max retries hit - excessive concurrent IPAM requests")
	}

	return nil, false, errors.New("failed to find or claim a block")
}

type IPAMAssignments struct {
	IPs              []net.IPNet       // assigned IP addresses
	IPVersion        int               // IP version (4 or 6)
	NumRequested     int               // number of requested IP addresses (not all may be assigned)
	HostReservedAttr *HostReservedAttr // reserved addresses at start and/or end of blocks
	Msgs             []string          // warning/error messages to be rendered in case there are any issues with the assignment
}

func (i *IPAMAssignments) AddMsg(msg string) {
	for _, m := range i.Msgs {
		if msg == m {
			// Don't add duplicate msgs
			return
		}
	}
	i.Msgs = append(i.Msgs, msg)
}

func (i *IPAMAssignments) PartialFulfillmentError() error {
	if len(i.IPs) < i.NumRequested {
		var b strings.Builder

		fmt.Fprintf(&b, "Assigned %d out of %d requested IPv%d addresses", len(i.IPs), i.NumRequested, i.IPVersion)

		for _, m := range i.Msgs {
			fmt.Fprintf(&b, "; %v", m)
		}

		if i.HostReservedAttr != nil {
			fmt.Fprintf(&b, "; HostReservedAttr: %v", i.HostReservedAttr.Handle)
		}

		return errors.New(b.String())
	}
	return nil
}

var ErrUseRequired = errors.New("must specify the intended use when assigning an IP")

func (c ipamClient) autoAssign(ctx context.Context, num int, handleID *string, attrs map[string]string, requestedPools []net.IPNet, version int, host string, maxNumBlocks int, rsvdAttr *HostReservedAttr, use v3.IPPoolAllowedUse) (*IPAMAssignments, error) {
	// Default parameters.
	if use == "" {
		log.Error("Attempting to auto-assign an IP without specifying intended use.")
		return nil, ErrUseRequired
	}

	// Load the set of reserved IPs/CIDRs.
	reservations, err := c.getReservedIPs(ctx)
	if err != nil {
		return nil, fmt.Errorf("failed to look up reserved IPs: %w", err)
	}

	// Get the existing host-affine blocks.
	logCtx := log.WithFields(log.Fields{"host": host})
	if handleID != nil {
		logCtx = logCtx.WithField("handle", *handleID)
	}
	logCtx.Info("Looking up existing affinities for host")
	pools, affBlocks, err := c.prepareAffinityBlocksForHost(ctx, requestedPools, version, host, rsvdAttr, use)
	if err != nil {
		return nil, err
	}

	logCtx.Debugf("Found %d affine IPv%d blocks for host: %v", len(affBlocks), version, affBlocks)

	// Record how many blocks we own so we can check against the limit later.
	numBlocksOwned := len(affBlocks)

	config, err := c.GetIPAMConfig(ctx)
	if err != nil {
		return nil, err
	}

	// Merge in any global config, if it exists. We use the more restrictive value between
	// the global max block limit, and the limit provided on this particular request.
	if config.MaxBlocksPerHost > 0 && maxNumBlocks > 0 && maxNumBlocks > config.MaxBlocksPerHost {
		// The global config is more restrictive, so use it instead.
		logCtx.Debugf("Global per-node block limit (%d) is more restrictive than per-request limit (%d), use it.", config.MaxBlocksPerHost, maxNumBlocks)
		maxNumBlocks = config.MaxBlocksPerHost
	} else if maxNumBlocks == 0 {
		// No per-request value, so use the global one.
		logCtx.Debug("No per-request block limit, using global value.")
		maxNumBlocks = config.MaxBlocksPerHost
	}

	if maxNumBlocks == 0 {
		// maxNumblocks is not defined. Default to a reasonable limit to act as a safeguard
		// against runaway block allocation. This limit can be overridden via config.
		logCtx.Debug("No max block config, defaulting to reasonable limit")
		maxNumBlocks = 20
	}
	logCtx.Debugf("Host must not use more than %d blocks", maxNumBlocks)

	ia := &IPAMAssignments{
		IPVersion:        version,
		NumRequested:     num,
		HostReservedAttr: rsvdAttr,
	}

	s := &blockAssignState{
		client:                c,
		version:               version,
		host:                  host,
		pools:                 pools,
		remainingAffineBlocks: affBlocks,
		hostReservedAttr:      rsvdAttr,
		allowNewClaim:         true,
		reservations:          reservations,
	}

	// Allocate the IPs.
	for len(ia.IPs) < num {
		var b *model.KVPair

		rem := num - len(ia.IPs)
		if maxNumBlocks > 0 && numBlocksOwned >= maxNumBlocks {
			s.allowNewClaim = false
		}

		b, newlyClaimed, err := s.findOrClaimBlock(ctx, 1)
		if err != nil {
			if _, ok := err.(noFreeBlocksError); ok {
				if config.StrictAffinity {
					ia.AddMsg("No more free affine blocks and strict affinity enabled")
				}

				// Skip to check non-affine blocks
				break
			}
			if errors.Is(err, ErrBlockLimit) {
				log.Warnf("Unable to allocate a new IPAM block; host already has %v blocks but "+
					"blocks per host limit is %v", numBlocksOwned, maxNumBlocks)
				ia.AddMsg(fmt.Sprintf("Need to allocate an IPAM block but could not - limit of %d blocks reached for this node", maxNumBlocks))
				return ia, ErrBlockLimit
			}
			return ia, err
		}

		if newlyClaimed {
			numBlocksOwned++
		}

		// We have got a block b.
		for i := 0; i < datastoreRetries; i++ {
			newIPs, err := c.assignFromExistingBlock(ctx, b, rem, handleID, attrs, host, config.StrictAffinity, reservations)
			if err != nil {
				if _, ok := err.(cerrors.ErrorResourceUpdateConflict); ok {
					log.WithError(err).Debug("CAS Error assigning from new block - retry")

					// At this point, block b's Unallocated field has been reduced already.
					// We should get the original block from datastore again.
					blockCIDR := b.Key.(model.BlockKey).CIDR
					b, err = c.blockReaderWriter.queryBlock(ctx, blockCIDR, "")
					if err != nil {
						logCtx.WithError(err).Warn("Failed to get block again after update conflict")
						break
					}

					// Block b is in sync with datastore. Retry assigning IP.
					continue
				}
				logCtx.WithError(err).Warningf("Failed to assign IPs in newly allocated block")
				ia.AddMsg("Failed to assign IPs in newly allocated block")
				break
			}
			logCtx.Debugf("Assigned IPs from new block: %s", newIPs)
			ia.IPs = append(ia.IPs, newIPs...)
			rem = num - len(ia.IPs)
			break
		}
	}

	// If there are still addresses to allocate, we've now tried all blocks
	// with some affinity to us, and tried (and failed) to allocate new
	// ones.  If we do not require strict host affinity, our last option is
	// a random hunt through any blocks we haven't yet tried.
	//
	// Note that this processing simply takes all of the IP pools and breaks
	// them up into block-sized CIDRs, then shuffles and searches through each
	// CIDR.  This algorithm does not work if we disallow auto-allocation of
	// blocks because the allocated blocks may be sparsely populated in the
	// pools resulting in a very slow search for free addresses.
	//
	// If we need to support non-strict affinity and no auto-allocation of
	// blocks, then we should query the actual allocation blocks and assign
	// from those.
	rem := num - len(ia.IPs)
	if config.StrictAffinity != true && rem != 0 {
		logCtx.Infof("Attempting to assign %d more addresses from non-affine blocks", rem)

		// Iterate over pools and assign addresses until we either run out of pools,
		// or the request has been satisfied.
		logCtx.Info("Looking for blocks with free IP addresses")
		exhaustedPools := []string{}
		for _, p := range pools {
			logCtx.Debugf("Assigning from non-affine blocks in pool %s", p.Spec.CIDR)
			newBlockCIDR := randomBlockGenerator(p, host)
			for rem > 0 {
				// Grab a new random block.
				blockCIDR := newBlockCIDR()
				if blockCIDR == nil {
					exhaustedPools = append(exhaustedPools, p.Spec.CIDR)
					logCtx.Warningf("All addresses exhausted in pool %s", p.Spec.CIDR)
					break
				}

				if reservations.MatchesWholeCIDR(blockCIDR) {
					log.WithField("cidr", blockCIDR).Debug("Skipping over reserved block")
					continue
				}

				for i := 0; i < datastoreRetries; i++ {
					b, err := c.blockReaderWriter.queryBlock(ctx, *blockCIDR, "")
					if err != nil {
						logCtx.WithError(err).Warn("Failed to get non-affine block")
						break
					}

					// Attempt to assign from the block.
					logCtx.Infof("Attempting to assign IPs from non-affine block %s", blockCIDR.String())
					newIPs, err := c.assignFromExistingBlock(ctx, b, rem, handleID, attrs, host, false, reservations)
					if err != nil {
						if _, ok := err.(cerrors.ErrorResourceUpdateConflict); ok {
							logCtx.WithError(err).Debug("CAS error assigning from non-affine block - retry")
							continue
						}
						logCtx.WithError(err).Warningf("Failed to assign IPs from non-affine block in pool %s", p.Spec.CIDR)
						break
					}
					if len(newIPs) == 0 {
						break
					}
					logCtx.Infof("Successfully assigned IPs from non-affine block %s", blockCIDR.String())
					ia.IPs = append(ia.IPs, newIPs...)
					rem = num - len(ia.IPs)
					break
				}
			}
		}
		if len(exhaustedPools) > 0 {
			ia.AddMsg(fmt.Sprintf("No IPs available in pools: %v", exhaustedPools))
		}
	}

	logCtx.Infof("Auto-assigned %d out of %d IPv%ds: %v", len(ia.IPs), num, version, ia.IPs)
	return ia, nil
}

// AssignIP assigns the provided IP address to the provided host.  The IP address
// must fall within a configured pool.  AssignIP will claim block affinity as needed
// in order to satisfy the assignment.  An error will be returned if the IP address
// is already assigned, or if StrictAffinity is enabled and the address is within
// a block that does not have affinity for the given host.
func (c ipamClient) AssignIP(ctx context.Context, args AssignIPArgs) error {
	hostname, err := decideHostname(args.Hostname)
	if err != nil {
		return err
	}
	log.Infof("Assigning IP %s to host: %s", args.IP, hostname)

	pool, err := c.blockReaderWriter.getPoolForIP(args.IP, nil)
	if err != nil {
		return err
	}
	if pool == nil {
		return errors.New("The provided IP address is not in a configured pool\n")
	}

	cfg, err := c.GetIPAMConfig(ctx)
	if err != nil {
		log.Errorf("Error getting IPAM Config: %v", err)
		return err
	}

	blockCIDR := getBlockCIDRForAddress(args.IP, pool)
	log.Debugf("IP %s is in block '%s'", args.IP.String(), blockCIDR.String())
	for i := 0; i < datastoreRetries; i++ {
		obj, err := c.blockReaderWriter.queryBlock(ctx, blockCIDR, "")
		if err != nil {
			if _, ok := err.(cerrors.ErrorResourceDoesNotExist); !ok {
				log.WithError(err).Error("Error getting block")
				return err
			}

			log.Debugf("Block for IP %s does not yet exist, creating", args.IP)
			cfg, err = c.GetIPAMConfig(ctx)
			if err != nil {
				log.Errorf("Error getting IPAM Config: %v", err)
				return err
			}

			pa, err := c.blockReaderWriter.getPendingAffinity(ctx, hostname, blockCIDR)
			if err != nil {
				if _, ok := err.(cerrors.ErrorResourceUpdateConflict); ok {
					log.WithError(err).Debug("CAS error claiming affinity for block - retry")
					continue
				}
				return err
			}

			obj, err = c.blockReaderWriter.claimAffineBlock(ctx, pa, *cfg, args.HostReservedAttr)
			if err != nil {
				if _, ok := err.(*errBlockClaimConflict); ok {
					log.Warningf("Someone else claimed block %s before us", blockCIDR.String())
					continue
				} else if _, ok := err.(cerrors.ErrorResourceUpdateConflict); ok {
					log.WithError(err).Debug("CAS error claiming affine block - retry")
					continue
				}
				log.WithError(err).Error("Error claiming block")
				return err
			}
			log.Infof("Claimed new block: %s", blockCIDR)
		}

		block := allocationBlock{obj.Value.(*model.AllocationBlock)}
		err = block.assign(cfg.StrictAffinity, args.IP, args.HandleID, args.Attrs, hostname)
		if err != nil {
			log.Errorf("Failed to assign address %v: %v", args.IP, err)
			return err
		}

		// Increment handle.
		if args.HandleID != nil {
			c.incrementHandle(ctx, *args.HandleID, blockCIDR, 1)
		}

		// Update the block using the original KVPair to do a CAS.  No need to
		// update the Value since we have been manipulating the Value pointed to
		// in the KVPair.
		_, err = c.blockReaderWriter.updateBlock(ctx, obj)
		if err != nil {
			if _, ok := err.(cerrors.ErrorResourceUpdateConflict); ok {
				log.WithError(err).Debug("CAS error assigning IP - retry")
				continue
			}

			log.WithError(err).Warningf("Update failed on block %s", block.CIDR.String())
			if args.HandleID != nil {
				if err := c.decrementHandle(ctx, *args.HandleID, blockCIDR, 1, nil); err != nil {
					log.WithError(err).Warn("Failed to decrement handle")
				}
			}
			return err
		}
		return nil
	}
	return errors.New("Max retries hit - excessive concurrent IPAM requests")
}

// ReleaseIPs releases any of the given IP addresses that are currently assigned,
// so that they are available to be used in another assignment.
func (c ipamClient) ReleaseIPs(ctx context.Context, ips ...ReleaseOptions) ([]net.IP, error) {
	for i := 0; i < len(ips); i++ {
		// Validate the input.
		if ips[i].Address == "" {
			return nil, fmt.Errorf("No IP address specified in options: %+v", ips[i])
		}

		// Sanitize any handles.
		ips[i].Handle = sanitizeHandle(ips[i].Handle)
	}

	log.Debugf("Releasing IP addresses: %v", ips)
	unallocated := []net.IP{}

	// Get IP pools up front so we don't need to query for each IP address.
	v4Pools, err := c.pools.GetEnabledPools(4)
	if err != nil {
		return nil, err
	}
	v6Pools, err := c.pools.GetEnabledPools(6)
	if err != nil {
		return nil, err
	}

	// Group IP addresses by block to minimize the number of writes
	// to the datastore required to release the given addresses.
	ipsByBlock := map[string][]ReleaseOptions{}
	for _, opts := range ips {
		var blockCIDR string

		ip, err := opts.AsNetIP()
		if err != nil {
			return nil, err
		}

		// Find the IP pools for this address in the enabled pools if possible.
		var pool *v3.IPPool
		switch ip.Version() {
		case 4:
			pool, err = c.blockReaderWriter.getPoolForIP(*ip, v4Pools)
			if err != nil {
				log.WithError(err).Warnf("Failed to get pool for IP")
				return nil, err
			}
		case 6:
			pool, err = c.blockReaderWriter.getPoolForIP(*ip, v6Pools)
			if err != nil {
				log.WithError(err).Warnf("Failed to get pool for IP")
				return nil, err
			}
		}

		if pool == nil {
			if cidr, err := c.blockReaderWriter.getBlockForIP(ctx, *ip); err != nil {
				return nil, err
			} else {
				if cidr == nil {
					// The IP isn't in any block so it's already unallocated.
					unallocated = append(unallocated, *ip)

					// Move on to the next IP
					continue
				}
				blockCIDR = cidr.String()
			}
		} else {
			blockCIDR = getBlockCIDRForAddress(*ip, pool).String()
		}

		// Check if we've already got an entry for this block.
		if _, exists := ipsByBlock[blockCIDR]; !exists {
			// Entry does not exist, create it.
			ipsByBlock[blockCIDR] = []ReleaseOptions{}
		}

		// Append to the list.
		ipsByBlock[blockCIDR] = append(ipsByBlock[blockCIDR], opts)
	}

	handleMap := map[string]*model.KVPair{}

	// If we're being asked to release several IP addresses, query all handles in order to
	// populate a cache. This reduces the number of queries required per-address.
	//
	// If we only have a handful of addresses to release, then we don't need to pre-fetch. It's
	// efficient enough to read each individually. Performing a List() of all handles (which can potentially
	// be very large) is more work than a few individual Get() requests, but less work than many Get() requests.
	if len(ips) > 2 {
		// List all handles, so we don't need to query them individually, and populate the map.
		allHandles, err := c.blockReaderWriter.listHandles(ctx, "")
		if err != nil {
			return unallocated, err
		}
		for _, h := range allHandles.KVPairs {
			handleMap[sanitizeHandle(h.Key.(model.IPAMHandleKey).HandleID)] = h
		}
	}

	// Release IPs for each block. These don't typically compete for resources, so we can do them in parallel
	// in order to move quickly. We start at most GOMAXPROCS goroutines at a time, each serving a single block.
	type retVal struct {
		Error       error
		Unallocated []net.IP
	}
	resultChan := make(chan retVal, len(ipsByBlock))
	sem := semaphore.NewWeighted(int64(runtime.GOMAXPROCS(-1)))
	for blockCIDR, ips := range ipsByBlock {
		if err := sem.Acquire(ctx, 1); err != nil {
			// Should only happen if the context finishes.
			log.WithError(err).Panic("Failed to acquire semaphore")
		}

		_, cidr, _ := net.ParseCIDR(blockCIDR)
		go func(cidr net.IPNet, ips []ReleaseOptions, hm map[string]*model.KVPair) {
			defer sem.Release(1)
			r := retVal{}
			unalloc, err := c.releaseIPsFromBlock(ctx, hm, ips, cidr)
			if err != nil {
				log.Errorf("Error releasing IPs: %v", err)
				r.Error = err
			}
			r.Unallocated = unalloc
			resultChan <- r
		}(*cidr, ips, handleMap)
	}

	// Read the response from each goroutine.
	err = nil
	for i := 0; i < len(ipsByBlock); i++ {
		r := <-resultChan
		log.Debugf("Received response #%d from release goroutine: %v", i, r)
		if r.Error != nil && err == nil {
			err = r.Error
		}
		unallocated = append(unallocated, r.Unallocated...)
	}
	return unallocated, err
}

func (c ipamClient) releaseIPsFromBlock(ctx context.Context, handleMap map[string]*model.KVPair, ips []ReleaseOptions, blockCIDR net.IPNet) ([]net.IP, error) {
	logCtx := log.WithField("cidr", blockCIDR)
	for i := 0; i < datastoreRetries; i++ {
		logCtx.Debug("Getting block so we can release IPs")

		// Get allocation block for cidr.
		obj, err := c.blockReaderWriter.queryBlock(ctx, blockCIDR, "")
		if err != nil {
			if _, ok := err.(cerrors.ErrorResourceDoesNotExist); ok {
				// The block does not exist - all addresses must be unassigned.
				unassigned := []net.IP{}
				for _, o := range ips {
					parsed := net.ParseIP(o.Address)
					if parsed == nil {
						return nil, fmt.Errorf("failed to parse the given IP: %s", o.Address)
					}
					unassigned = append(unassigned, *parsed)
				}
				return unassigned, nil
			} else {
				// Unexpected error reading block.
				return nil, err
			}
		}

		// Release the IPs.
		b := allocationBlock{obj.Value.(*model.AllocationBlock)}
		unallocated, handles, err2 := b.release(ips)
		if err2 != nil {
			return nil, err2
		}
		if len(ips) == len(unallocated) {
			// All the given IP addresses are already unallocated.
			// Just return.
			logCtx.Debug("No IPs need to be released")
			return unallocated, nil
		}

		// If the block is empty and has no affinity, we can delete it.
		// Otherwise, update the block using CAS.  There is no need to update
		// the Value since we have updated the structure pointed to in the
		// KVPair.
		var updateErr error
		if b.empty() && b.Affinity == nil {
			logCtx.Info("Deleting non-affine block")
			updateErr = c.blockReaderWriter.deleteBlock(ctx, obj)
		} else {
			logCtx.Info("Updating assignments in block")
			_, updateErr = c.blockReaderWriter.updateBlock(ctx, obj)
		}

		if updateErr != nil {
			if _, ok := updateErr.(cerrors.ErrorResourceUpdateConflict); ok {
				// Comparison error - retry.
				logCtx.Warningf("Failed to update block - retry #%d", i)
				continue
			} else {
				// Something else - return the error.
				logCtx.WithError(updateErr).Errorf("Error updating block")
				return nil, updateErr
			}
		}

		// Success - decrement handles.
		logCtx.Debugf("Decrementing handles: %v", handles)
		for handleID, amount := range handles {
			if err := c.decrementHandle(ctx, handleID, blockCIDR, amount, handleMap[handleID]); err != nil {
				logCtx.WithError(err).Warn("Failed to decrement handle")
			}
		}

		// Determine whether or not the block's pool still matches the node.
		if err := c.ensureConsistentAffinity(ctx, obj.Value.(*model.AllocationBlock)); err != nil {
			logCtx.WithError(err).Warn("Error ensuring consistent affinity but IP already released. Returning no error.")
		}
		return unallocated, nil
	}
	return nil, errors.New("Max retries hit - excessive concurrent IPAM requests")
}

func (c ipamClient) assignFromExistingBlock(ctx context.Context, block *model.KVPair, num int, handleID *string, attrs map[string]string, host string, affCheck bool, reservations addrFilter) ([]net.IPNet, error) {
	blockCIDR := block.Key.(model.BlockKey).CIDR
	logCtx := log.WithFields(log.Fields{"host": host, "block": blockCIDR})
	if handleID != nil {
		logCtx = logCtx.WithField("handle", *handleID)
	}
	logCtx.Infof("Attempting to assign %d addresses from block", num)

	// Pull out the block.
	b := allocationBlock{block.Value.(*model.AllocationBlock)}

	ips, err := b.autoAssign(num, handleID, host, attrs, affCheck, reservations)
	if err != nil {
		logCtx.WithError(err).Errorf("Error in auto assign")
		return nil, err
	}
	if len(ips) == 0 {
		logCtx.Infof("Block is full")
		return []net.IPNet{}, nil
	}

	// Increment handle count.
	if handleID != nil {
		logCtx.Debug("Incrementing handle")
		c.incrementHandle(ctx, *handleID, blockCIDR, num)
	}

	// Update the block using CAS by passing back the original
	// KVPair.
	logCtx.Info("Writing block in order to claim IPs")
	block.Value = b.AllocationBlock
	_, err = c.blockReaderWriter.updateBlock(ctx, block)
	if err != nil {
		logCtx.WithError(err).Infof("Failed to update block")
		if handleID != nil {
			logCtx.Debug("Decrementing handle since we failed to allocate IP(s)")
			if err := c.decrementHandle(ctx, *handleID, blockCIDR, num, nil); err != nil {
				logCtx.WithError(err).Warnf("Failed to decrement handle")
			}
		}
		return nil, err
	}
	logCtx.Infof("Successfully claimed IPs: %v", ips)
	return ips, nil
}

// ClaimAffinity makes a best effort to claim affinity to the given host for all blocks
// within the given CIDR.  The given CIDR must fall within a configured
// pool.  Returns a list of blocks that were claimed, as well as a
// list of blocks that were claimed by another host.
// If an empty string is passed as the host, then the hostname is automatically detected.
func (c ipamClient) ClaimAffinity(ctx context.Context, cidr net.IPNet, host string) ([]net.IPNet, []net.IPNet, error) {
	logCtx := log.WithFields(log.Fields{"host": host, "cidr": cidr})

	// Verify the requested CIDR falls within a configured pool.
	pool, err := c.blockReaderWriter.getPoolForIP(net.IP{IP: cidr.IP}, nil)
	if err != nil {
		return nil, nil, err
	}
	if pool == nil {
		estr := fmt.Sprintf("The requested CIDR (%s) is not within any configured pools.", cidr.String())
		return nil, nil, errors.New(estr)
	}

	// Validate that the given CIDR is at least as big as a block.
	if !largerThanOrEqualToBlock(cidr, pool) {
		estr := fmt.Sprintf("The requested CIDR (%s) is smaller than the minimum.", cidr.String())
		return nil, nil, invalidSizeError(estr)
	}

	// Determine the hostname to use.
	hostname, err := decideHostname(host)
	if err != nil {
		return nil, nil, err
	}

	failed := []net.IPNet{}
	claimed := []net.IPNet{}

	// Get IPAM config.
	cfg, err := c.GetIPAMConfig(ctx)
	if err != nil {
		logCtx.Errorf("Failed to get IPAM Config: %v", err)
		return nil, nil, err
	}

	// Claim all blocks within the given cidr.
	blocks := blockGenerator(pool, cidr)
	for blockCIDR := blocks(); blockCIDR != nil; blockCIDR = blocks() {
		for i := 0; i < datastoreRetries; i++ {
			// First, claim a pending affinity.
			pa, err := c.blockReaderWriter.getPendingAffinity(ctx, hostname, *blockCIDR)
			if err != nil {
				if _, ok := err.(cerrors.ErrorResourceUpdateConflict); ok {
					logCtx.WithError(err).Debug("CAS error getting pending affinity - retry")
					continue
				}
				return claimed, failed, err
			}

			// Once we have the affinity, claim the block, which will confirm the affinity.
			_, err = c.blockReaderWriter.claimAffineBlock(ctx, pa, *cfg, nil)
			if err != nil {
				if _, ok := err.(cerrors.ErrorResourceUpdateConflict); ok {
					logCtx.WithError(err).Debug("CAS error claiming affine block - retry")
					continue
				} else if _, ok := err.(errBlockClaimConflict); ok {
					logCtx.Debugf("Block %s is claimed by another host", blockCIDR.String())
					failed = append(failed, *blockCIDR)
				} else {
					logCtx.Errorf("Failed to claim block: %v", err)
					return claimed, failed, err
				}
			} else {
				logCtx.Debugf("Claimed CIDR %s", blockCIDR.String())
				claimed = append(claimed, *blockCIDR)
			}
			break
		}
	}
	return claimed, failed, nil
}

// ReleaseAffinity releases affinity for all blocks within the given CIDR
// on the given host.  If a block does not have affinity for the given host,
// its affinity will not be released and no error will be returned.
// If an empty string is passed as the host, then the hostname is automatically detected.
func (c ipamClient) ReleaseAffinity(ctx context.Context, cidr net.IPNet, host string, mustBeEmpty bool) error {
	// Verify the requested CIDR falls within a configured pool.
	fields := log.Fields{"cidr": cidr.String(), "host": host, "mustBeEmpty": mustBeEmpty}
	log.WithFields(fields).Debugf("Releasing affinity for CIDR")
	pool, err := c.blockReaderWriter.getPoolForIP(net.IP{IP: cidr.IP}, nil)
	if err != nil {
		return err
	}
	if pool == nil {
		estr := fmt.Sprintf("The requested CIDR (%s) is not within any configured pools.", cidr.String())
		return errors.New(estr)
	}

	// Validate that the given CIDR is at least as big as a block.
	if !largerThanOrEqualToBlock(cidr, pool) {
		estr := fmt.Sprintf("The requested CIDR (%s) is smaller than the minimum.", cidr.String())
		return invalidSizeError(estr)
	}

	// Determine the hostname to use.
	hostname, err := decideHostname(host)
	if err != nil {
		return err
	}

	// Release all blocks within the given cidr.
	blocks := blockGenerator(pool, cidr)
	for blockCIDR := blocks(); blockCIDR != nil; blockCIDR = blocks() {
		logCtx := log.WithField("cidr", blockCIDR)
		for i := 0; i < datastoreRetries; i++ {
			err := c.blockReaderWriter.releaseBlockAffinity(ctx, hostname, *blockCIDR, mustBeEmpty)
			if err != nil {
				if _, ok := err.(errBlockClaimConflict); ok {
					// Not claimed by this host - ignore.
				} else if _, ok := err.(cerrors.ErrorResourceDoesNotExist); ok {
					// Block does not exist - ignore.
				} else if _, ok := err.(cerrors.ErrorResourceUpdateConflict); ok {
					logCtx.WithError(err).Debug("CAS error releasing block affinity - retry")
					continue
				} else {
					logCtx.WithError(err).Errorf("Error releasing affinity")
					return err
				}
			}
			break
		}
	}
	return nil
}

// Releases the affinity for the given block.
func (c ipamClient) ReleaseBlockAffinity(ctx context.Context, block *model.AllocationBlock, mustBeEmpty bool) error {
	blockCIDR := block.CIDR.String()
	logCtx := log.WithField("cidr", blockCIDR)

	if block.Affinity == nil {
		logCtx.Info("Block is already released")
		return nil
	}
	hostname := getHostAffinity(block)

	err := c.blockReaderWriter.releaseBlockAffinity(ctx, hostname, block.CIDR, mustBeEmpty)
	if err != nil {
		if _, ok := err.(errBlockClaimConflict); ok {
			// Not claimed by this host - ignore.
		} else if _, ok := err.(cerrors.ErrorResourceDoesNotExist); ok {
			// Block does not exist - ignore.
		} else {
			logCtx.WithError(err).Errorf("Failed to release block affinity")
			return err
		}
	}
	return nil
}

// ReleaseHostAffinities releases affinity for all blocks that are affine
// to the given host.  If an empty string is passed as the host,
// then the hostname is automatically detected.
func (c ipamClient) ReleaseHostAffinities(ctx context.Context, host string, mustBeEmpty bool) error {
	log.Debugf("Releasing affinities for host %s. MustBeEmpty? %v", host, mustBeEmpty)
	hostname, err := decideHostname(host)
	if err != nil {
		return err
	}

	var storedError error
	versions := []int{4, 6}
	for _, version := range versions {
		blockCIDRs, err := c.blockReaderWriter.getAffineBlocks(ctx, hostname, version)
		if err != nil {
			return err
		}

		for _, blockCIDR := range blockCIDRs {
			logCtx := log.WithField("cidr", blockCIDR)
			for i := 0; i < datastoreRetries; i++ {
				err := c.blockReaderWriter.releaseBlockAffinity(ctx, host, blockCIDR, mustBeEmpty)
				if err != nil {
					if _, ok := err.(errBlockClaimConflict); ok {
						// Claimed by a different host. Move to next block.
					} else if _, ok := err.(cerrors.ErrorResourceDoesNotExist); ok {
						// Block does not exist - move to next block.
					} else if _, ok := err.(cerrors.ErrorResourceUpdateConflict); ok {
						logCtx.WithError(err).Debug("CAS error releasing block affinity - retry")
						continue
					} else {
						// Store the error for later so we can return it.
						// We don't want to return just yet so we can do a best-effort
						// attempt at releasing the other CIDRs for this host.
						storedError = err
					}
				}

				// Break out of the inner retry loop.
				break
			}
		}
	}
	return storedError
}

// ReleasePoolAffinities releases affinity for all blocks within
// the specified pool across all hosts.
func (c ipamClient) ReleasePoolAffinities(ctx context.Context, pool net.IPNet) error {
	log.Infof("Releasing block affinities within pool '%s'", pool.String())
	for i := 0; i < ipamKeyErrRetries; i++ {
		retry := false
		pairs, err := c.hostBlockPairs(ctx, pool)
		if err != nil {
			return err
		}

		if len(pairs) == 0 {
			log.Debugf("No blocks have affinity")
			return nil
		}

		for blockString, host := range pairs {
			_, blockCIDR, _ := net.ParseCIDR(blockString)
			logCtx := log.WithField("cidr", blockCIDR)
			for i := 0; i < datastoreRetries; i++ {
				err = c.blockReaderWriter.releaseBlockAffinity(ctx, host, *blockCIDR, false)
				if err != nil {
					if _, ok := err.(errBlockClaimConflict); ok {
						retry = true
					} else if _, ok := err.(cerrors.ErrorResourceDoesNotExist); ok {
						logCtx.Debugf("No such block")
						break
					} else if _, ok := err.(cerrors.ErrorResourceUpdateConflict); ok {
						logCtx.WithError(err).Debug("CAS error releasing block affinity - retry")
						continue
					} else {
						logCtx.WithError(err).Errorf("Error releasing affinity")
						return err
					}
				}
				break
			}
		}

		if !retry {
			return nil
		}
	}
	return errors.New("Max retries hit - excessive concurrent IPAM requests")
}

// RemoveIPAMHost releases affinity for all blocks on the given host,
// and removes all host-specific IPAM data from the datastore.
// RemoveIPAMHost does not release any IP addresses claimed on the given host.
// If an empty string is passed as the host, then the hostname is automatically detected.
func (c ipamClient) RemoveIPAMHost(ctx context.Context, host string) error {
	// Determine the hostname to use.
	hostname, err := decideHostname(host)
	if err != nil {
		return err
	}
	logCtx := log.WithField("host", hostname)
	logCtx.Debug("Removing IPAM data for host")

	for i := 0; i < datastoreRetries; i++ {
		// Release affinities for this host.
		logCtx.Debug("Releasing IPAM affinities for host")
		if err := c.ReleaseHostAffinities(ctx, hostname, false); err != nil {
			logCtx.WithError(err).Errorf("Failed to release IPAM affinities for host")
			return err
		}

		// Get the IPAM host.
		logCtx.Debug("Querying IPAM host tree in data store")
		k := model.IPAMHostKey{Host: hostname}
		kvp, err := c.client.Get(ctx, k, "")
		if err != nil {
			if _, ok := err.(cerrors.ErrorOperationNotSupported); ok {
				// KDD mode doesn't have this object - this is a no-op.
				logCtx.Debugf("No need to remove IPAM host for this datastore")
				return nil
			}
			if _, ok := err.(cerrors.ErrorResourceDoesNotExist); !ok {
				logCtx.WithError(err).Errorf("Failed to get IPAM host")
				return err
			}

			// Resource does not exist, no need to remove it.
			logCtx.Debug("IPAM host data does not exist")
			return nil
		}

		// Remove the host tree from the datastore.
		logCtx.Debug("Deleting IPAM host tree from data store")
		_, err = c.client.Delete(ctx, k, kvp.Revision)
		if err != nil {
			if _, ok := err.(cerrors.ErrorResourceUpdateConflict); ok {
				// We hit a compare-and-delete error - retry.
				continue
			}

			// Return the error unless the resource does not exist.
			if _, ok := err.(cerrors.ErrorResourceDoesNotExist); !ok {
				logCtx.Errorf("Error removing IPAM host: %v", err)
				return err
			}
		}
		logCtx.Debug("Successfully deleted IPAM host data")
		return nil
	}

	return errors.New("Max retries hit")
}

func (c ipamClient) hostBlockPairs(ctx context.Context, pool net.IPNet) (map[string]string, error) {
	pairs := map[string]string{}

	// Get all blocks and their affinities.
	objs, err := c.client.List(ctx, model.BlockAffinityListOptions{}, "")
	if err != nil {
		log.Errorf("Error querying block affinities: %v", err)
		return nil, err
	}

	// Iterate through each block affinity and build up a mapping
	// of blockCidr -> host.
	log.Debugf("Getting block -> host mappings")
	for _, o := range objs.KVPairs {
		k := o.Key.(model.BlockAffinityKey)

		// Only add the pair to the map if the block belongs to the pool.
		if pool.Contains(k.CIDR.IPNet.IP) {
			pairs[k.CIDR.String()] = k.Host
		}
		log.Debugf("Block %s -> %s", k.CIDR.String(), k.Host)
	}

	return pairs, nil
}

// IpsByHandle returns a list of all IP addresses that have been
// assigned using the provided handle.
func (c ipamClient) IPsByHandle(ctx context.Context, handleID string) ([]net.IP, error) {
	obj, err := c.blockReaderWriter.queryHandle(ctx, handleID, "")
	if err != nil {
		return nil, err
	}
	handle := allocationHandle{obj.Value.(*model.IPAMHandle)}

	assignments := []net.IP{}
	for k := range handle.Block {
		_, blockCIDR, _ := net.ParseCIDR(k)
		obj, err := c.blockReaderWriter.queryBlock(ctx, *blockCIDR, "")
		if err != nil {
			log.WithError(err).Warningf("Couldn't read block %s referenced by handle %s", blockCIDR, handleID)
			continue
		}

		// Pull out the allocationBlock and get all the assignments from it.
		b := allocationBlock{obj.Value.(*model.AllocationBlock)}
		assignments = append(assignments, b.ipsByHandle(handleID)...)
	}
	return assignments, nil
}

// ReleaseByHandle releases all IP addresses that have been assigned
// using the provided handle.
func (c ipamClient) ReleaseByHandle(ctx context.Context, handleID string) error {
	handleID = sanitizeHandle(handleID)
	log.Debugf("Releasing all IPs with handle '%s'", handleID)
	obj, err := c.blockReaderWriter.queryHandle(ctx, handleID, "")
	if err != nil {
		return err
	}
	handle := allocationHandle{obj.Value.(*model.IPAMHandle)}

	for blockStr := range handle.Block {
		_, blockCIDR, _ := net.ParseCIDR(blockStr)
		if err := c.releaseByHandle(ctx, *blockCIDR, ReleaseOptions{Handle: handleID}); err != nil {
			return err
		}
	}
	return nil
}

func (c ipamClient) releaseByHandle(ctx context.Context, blockCIDR net.IPNet, opts ReleaseOptions) error {
	logCtx := log.WithFields(log.Fields{"handle": opts.Handle, "cidr": blockCIDR})
	for i := 0; i < datastoreRetries; i++ {
		logCtx.Debug("Querying block so we can release IPs by handle")
		obj, err := c.blockReaderWriter.queryBlock(ctx, blockCIDR, "")
		if err != nil {
			if _, ok := err.(cerrors.ErrorResourceDoesNotExist); ok {
				// Block doesn't exist, so all addresses are already
				// unallocated.  This can happen when a handle is
				// overestimating the number of assigned addresses.
				return nil
			} else {
				return err
			}
		}

		// Release the IP by handle.
		block := allocationBlock{obj.Value.(*model.AllocationBlock)}
		num := block.releaseByHandle(opts)
		if num == 0 {
			// Block has no addresses with this handle, so
			// all addresses are already unallocated.
			logCtx.Debug("Block has no addresses with the given handle")
			return nil
		}
		logCtx.Debugf("Block has %d IPs with the given handle", num)

		if block.empty() && block.Affinity == nil {
			logCtx.Info("Deleting block because it is now empty and has no affinity")
			err = c.blockReaderWriter.deleteBlock(ctx, obj)
			if err != nil {
				if _, ok := err.(cerrors.ErrorResourceUpdateConflict); ok {
					logCtx.Debug("CAD error deleting block - retry")
					continue
				}

				// Return the error unless the resource does not exist.
				if _, ok := err.(cerrors.ErrorResourceDoesNotExist); !ok {
					logCtx.Errorf("Error deleting block: %v", err)
					return err
				}
			}
			logCtx.Info("Successfully deleted empty block")
		} else {
			// Compare and swap the AllocationBlock using the original
			// KVPair read from before.  No need to update the Value since we
			// have been directly manipulating the value referenced by the KVPair.
			logCtx.Debug("Updating block to release IPs")
			_, err = c.blockReaderWriter.updateBlock(ctx, obj)
			if err != nil {
				if _, ok := err.(cerrors.ErrorResourceUpdateConflict); ok {
					// Comparison failed - retry.
					logCtx.Warningf("CAS error for block, retry #%d: %v", i, err)
					continue
				} else {
					// Something else - return the error.
					logCtx.Errorf("Error updating block '%s': %v", block.CIDR.String(), err)
					return err
				}
			}
			logCtx.Debug("Successfully released IPs from block")
		}
		if err = c.decrementHandle(ctx, opts.Handle, blockCIDR, num, nil); err != nil {
			logCtx.WithError(err).Warn("Failed to decrement handle")
		}

		// Determine whether or not the block's pool still matches the node.
		if err = c.ensureConsistentAffinity(ctx, block.AllocationBlock); err != nil {
			logCtx.WithError(err).Warn("Error ensuring consistent affinity but IP already released. Returning no error.")
		}
		return nil
	}
	return errors.New("Hit max retries")
}

func (c ipamClient) incrementHandle(ctx context.Context, handleID string, blockCIDR net.IPNet, num int) error {
	var obj *model.KVPair
	var err error
	for i := 0; i < datastoreRetries; i++ {
		obj, err = c.blockReaderWriter.queryHandle(ctx, handleID, "")
		if err != nil {
			if _, ok := err.(cerrors.ErrorResourceDoesNotExist); ok {
				// Handle doesn't exist - create it.
				log.Infof("Creating new handle: %s", handleID)
				bh := model.IPAMHandle{
					HandleID: handleID,
					Block:    map[string]int{},
				}
				obj = &model.KVPair{
					Key:   model.IPAMHandleKey{HandleID: handleID},
					Value: &bh,
				}
			} else {
				// Unexpected error reading handle.
				return err
			}
		}

		// Get the handle from the KVPair.
		handle := allocationHandle{obj.Value.(*model.IPAMHandle)}

		// Increment the handle for this block.
		handle.incrementBlock(blockCIDR, num)

		// Compare and swap the handle using the KVPair from above.  We've been
		// manipulating the structure in the KVPair, so pass straight back to
		// apply the changes.
		if obj.Revision != "" {
			// This is an existing handle - update it.
			_, err = c.blockReaderWriter.updateHandle(ctx, obj)
			if err != nil {
				log.WithError(err).Warning("Failed to update handle, retry")
				continue
			}
		} else {
			// This is a new handle - create it.
			_, err = c.client.Create(ctx, obj)
			if err != nil {
				log.WithError(err).Warning("Failed to create handle, retry")
				continue
			}
		}
		return nil
	}
	return errors.New("Max retries hit - excessive concurrent IPAM requests")
}

func (c ipamClient) decrementHandle(ctx context.Context, handleID string, blockCIDR net.IPNet, num int, obj *model.KVPair) error {
	for i := 0; i < datastoreRetries; i++ {
		var err error
		// Query the handle if either of these conditions is true:
		// - This is the first iteration, and the caller did not provide the current handle.
		// - This is a retry.
		if (i == 0 && obj == nil) || i != 0 {
			obj, err = c.blockReaderWriter.queryHandle(ctx, handleID, "")
			if err != nil {
				return err
			}
		}
		handle := allocationHandle{obj.Value.(*model.IPAMHandle)}

		_, err = handle.decrementBlock(blockCIDR, num)
		if err != nil {
			return err
		}

		// Update / Delete as appropriate.  Since we have been manipulating the
		// data in the KVPair, just pass this straight back to the client.
		if handle.empty() {
			log.Debugf("Deleting handle: %s", handleID)
			if err = c.blockReaderWriter.deleteHandle(ctx, obj); err != nil {
				if err != nil {
					if _, ok := err.(cerrors.ErrorResourceUpdateConflict); ok {
						// Update conflict - retry.
						continue
					} else if _, ok := err.(cerrors.ErrorResourceDoesNotExist); !ok {
						return err
					}
					// Already deleted.
				}
			}
		} else {
			log.Debugf("Updating handle: %s", handleID)
			if _, err = c.blockReaderWriter.updateHandle(ctx, obj); err != nil {
				if _, ok := err.(cerrors.ErrorResourceUpdateConflict); ok {
					// Update conflict - retry.
					continue
				}
				return err
			}
		}

		log.Debugf("Decremented handle '%s' by %d", handleID, num)
		return nil
	}
	return errors.New("Max retries hit - excessive concurrent IPAM requests")
}

// GetAssignmentAttributes returns the attributes stored with the given IP address
// upon assignment, as well as the handle used for assignment (if any).
func (c ipamClient) GetAssignmentAttributes(ctx context.Context, addr net.IP) (map[string]string, *string, error) {
	pool, err := c.blockReaderWriter.getPoolForIP(addr, nil)
	if err != nil {
		return nil, nil, err
	}
	if pool == nil {
		log.Errorf("Error reading pool for %s", addr.String())
		return nil, nil, cerrors.ErrorResourceDoesNotExist{Identifier: addr.String(), Err: errors.New("No valid IPPool")}
	}
	blockCIDR := getBlockCIDRForAddress(addr, pool)
	obj, err := c.blockReaderWriter.queryBlock(ctx, blockCIDR, "")
	if err != nil {
		log.Errorf("Error reading block %s: %v", blockCIDR, err)
		return nil, nil, err
	}
	block := allocationBlock{obj.Value.(*model.AllocationBlock)}
	attrs, err := block.attributesForIP(addr)
	if err != nil {
		return nil, nil, err
	}
	handle, err := block.handleForIP(addr)
	if err != nil {
		return nil, nil, err
	}
	return attrs, handle, nil
}

// GetIPAMConfig returns the global IPAM configuration.  If no IPAM configuration
// has been set, returns a default configuration with StrictAffinity disabled
// and AutoAllocateBlocks enabled.
func (c ipamClient) GetIPAMConfig(ctx context.Context) (*IPAMConfig, error) {
	var obj *model.KVPair
	var err error
	var retries int

	maxRetry := 5

	// Try to get the IPAM Config. If it doesn't exist, we'll attempt to create it.
	for retries = 1; retries < maxRetry; retries++ {
		if ctx.Err() != nil {
			return nil, ctx.Err()
		}

		obj, err = c.client.Get(ctx, model.IPAMConfigKey{}, "")
		if err != nil {
			if _, ok := err.(cerrors.ErrorResourceDoesNotExist); !ok {
				// Unexpected error querying the IPAM config.
				log.WithError(err).Errorf("Error getting IPAM config")
				return nil, err
			}

			// Create the default config because it doesn't already exist.
			kvp := &model.KVPair{
				Key: model.IPAMConfigKey{},
				Value: &model.IPAMConfig{
					StrictAffinity:     false,
					AutoAllocateBlocks: true,
					MaxBlocksPerHost:   0,
				},
			}

			obj, err = c.client.Create(ctx, kvp)
			if err != nil {
				if _, ok := err.(cerrors.ErrorResourceAlreadyExists); ok {
					log.Info("Failed to create global IPAM config; another node got there first.")
					time.Sleep(1 * time.Second)
					continue
				}
				log.WithError(err).Errorf("Error creating IPAM config")
				return nil, err
			}
		}
		break
	}

	if retries >= maxRetry {
		return nil, fmt.Errorf("failed to get ipam config after %d retries", retries)
	}

	config := c.convertBackendToIPAMConfig(obj.Value.(*model.IPAMConfig))

	if detectOS(ctx) == "windows" {
		// When a Windows node owns a block, it creates a local /26 subnet object and as far as we know, it can't
		// do a longest-prefix-match between the subnet CIDR and a remote /32.  This means that we can't allow
		// remote hosts to borrow IPs from a Windows-owned block; and Windows hosts can't borrow IPs either.
		// Return error if strict affinity is not true.
		if !config.StrictAffinity {
			err = ErrStrictAffinity
			log.WithError(err).Error("Error validating ipam config")
			return nil, err
		}
	}
	return config, nil
}

// SetIPAMConfig sets global IPAM configuration.  This can only
// be done when there are no allocated blocks and IP addresses.
func (c ipamClient) SetIPAMConfig(ctx context.Context, cfg IPAMConfig) error {
	current, err := c.GetIPAMConfig(ctx)
	if err != nil {
		return err
	}

	if *current == cfg {
		return nil
	}

	if !cfg.StrictAffinity && !cfg.AutoAllocateBlocks {
		return errors.New("Cannot disable 'StrictAffinity' and 'AutoAllocateBlocks' at the same time")
	}

	if cfg.MaxBlocksPerHost > 0 && !cfg.StrictAffinity {
		// MaxBlocksPerHost always takes effect before StrictAffinity,
		// so require the user to be explicit in order to prevent confusing behavior, and to
		// ensure that our code behaves consistently even in places where MaxBlocksPerHost isn't checked.
		return errors.New("MaxBlocksPerHost requires StrictAffinity to be enabled")
	}

	// Get revision if resource already exists
	old, err := c.client.Get(ctx, model.IPAMConfigKey{}, "")
	if err != nil {
		if _, ok := err.(cerrors.ErrorResourceDoesNotExist); !ok {
			log.Errorf("Error querying IPAMConfig %v", err)
			return err
		}
	}

	// Write to datastore.
	obj := model.KVPair{
		Key:   model.IPAMConfigKey{},
		Value: c.convertIPAMConfigToBackend(&cfg),
	}
	if old != nil {
		obj.Revision = old.Revision
	}
	_, err = c.client.Apply(ctx, &obj)
	if err != nil {
		log.Errorf("Error applying IPAMConfig: %v", err)
		return err
	}

	return nil
}

func (c ipamClient) convertIPAMConfigToBackend(cfg *IPAMConfig) *model.IPAMConfig {
	return &model.IPAMConfig{
		StrictAffinity:     cfg.StrictAffinity,
		AutoAllocateBlocks: cfg.AutoAllocateBlocks,
		MaxBlocksPerHost:   cfg.MaxBlocksPerHost,
	}
}

func (c ipamClient) convertBackendToIPAMConfig(cfg *model.IPAMConfig) *IPAMConfig {
	return &IPAMConfig{
		StrictAffinity:     cfg.StrictAffinity,
		AutoAllocateBlocks: cfg.AutoAllocateBlocks,
		MaxBlocksPerHost:   cfg.MaxBlocksPerHost,
	}
}

// ensureConsistentAffinity retrieves the pool and node for the given block and determines
// if the pool still selects node. If it no longer matches, it will release the block
// affinity for that node.
// Returns a bool indicating if the block affinity was released.
func (c ipamClient) ensureConsistentAffinity(ctx context.Context, b *model.AllocationBlock) error {
	// Retrieve node for this allocation. We do this so we can clean up affinity for blocks
	// which should no longer be affine to this host.
	host := getHostAffinity(b)
	logCtx := log.WithFields(log.Fields{"cidr": b.CIDR, "host": host})

	// If no hostname is found on the block affinity,
	// there is no need to do an ip pool node selection check.
	if host == "" {
		logCtx.Debug("Block already has no affinity")
		return nil
	}

	// If the IP pool which owns this block no longer selects this node,
	// we should release the block's affinity to this node so it can be
	// used elsewhere.
	logCtx.Debugf("Looking up node labels for host affinity")
	node, err := c.client.Get(ctx, model.ResourceKey{Kind: libapiv3.KindNode, Name: host}, "")
	if err != nil {
		if _, ok := err.(cerrors.ErrorResourceDoesNotExist); !ok {
			logCtx.WithError(err).WithField("node", host).Error("Failed to get node for host")
			return err
		}
		logCtx.Info("Node doesn't exist, no need to release affinity")
		return nil
	}

	// Make sure the returned value is a valid node.
	v3n, ok := node.Value.(*libapiv3.Node)
	if !ok {
		return fmt.Errorf("Datastore returned malformed node object")
	}

	// Fetch the pool for the given CIDR and check if it selects the node.
	pool, err := c.blockReaderWriter.getPoolForIP(net.IP{IP: b.CIDR.IPNet.IP}, nil)
	if err != nil {
		return err
	}

	if pool == nil {
		logCtx.Debug("No pools own this block")
		return nil
	} else if sel, err := SelectsNode(*pool, *v3n); err != nil {
		logCtx.WithField("selector", pool.Spec.NodeSelector).WithError(err).Error("Failed to determine node selection")
		return err
	} else if sel {
		logCtx.Debug("Pool selects node, no change")
		return nil
	}
	logCtx.WithField("selector", pool.Spec.NodeSelector).Debug("Pool no longer selects node, releasing block affinity")

	// Pool does not match this node's label, release this block's affinity.
	if err = c.blockReaderWriter.releaseBlockAffinity(ctx, host, b.CIDR, true); err != nil {
		if _, ok := err.(errBlockClaimConflict); ok {
			// Not claimed by this host - ignore.
		} else if _, ok := err.(errBlockNotEmpty); ok {
			// Block isn't empty - ignore.
		} else if _, ok := err.(cerrors.ErrorResourceDoesNotExist); ok {
			// Block does not exist - ignore.
		} else {
			return err
		}
	}

	return nil
}

func decideHostname(host string) (string, error) {
	// Determine the hostname to use - prefer the provided hostname if
	// non-nil, otherwise use the hostname reported by os.
	var hostname string
	var err error
	if host != "" {
		hostname = host
	} else {
		hostname, err = names.Hostname()
		if err != nil {
			return "", fmt.Errorf("Failed to acquire hostname: %+v", err)
		}
	}
	log.Debugf("Using hostname=%s", hostname)
	return hostname, nil
}

// GetUtilization returns IP utilization info for the specified pools, or for all pools.
func (c ipamClient) GetUtilization(ctx context.Context, args GetUtilizationArgs) ([]*PoolUtilization, error) {
	var usage []*PoolUtilization

	// Read all pools.
	allPools, err := c.pools.GetAllPools()
	if err != nil {
		log.WithError(err).Errorf("Error getting IP pools")
		return nil, err
	}

	// Identify the ones we want and create a PoolUtilization for each of those.
	wantAllPools := len(args.Pools) == 0
	wantedPools := set.FromArray(args.Pools)
	for _, pool := range allPools {
		if wantAllPools ||
			wantedPools.Contains(pool.Name) ||
			wantedPools.Contains(pool.Spec.CIDR) {
			usage = append(usage, &PoolUtilization{
				Name: pool.Name,
				CIDR: net.MustParseNetwork(pool.Spec.CIDR).IPNet,
			})
		}
	}

	// If we've been asked for all pools, also report utilization for any allocation
	// blocks for which there is no longer an IP pool.  Note: following code depends
	// on this being at the end of the list; otherwise it will suck in allocation
	// blocks that should be reported under other pools.
	if wantAllPools {
		usage = append(usage, &PoolUtilization{
			Name: "orphaned allocation blocks",
			CIDR: net.MustParseNetwork("0.0.0.0/0").IPNet,
		})
	}

	// Read all allocation blocks.
	blocks, err := c.client.List(ctx, model.BlockListOptions{}, "")
	if err != nil {
		return nil, err
	}
	for _, kvp := range blocks.KVPairs {
		b := kvp.Value.(*model.AllocationBlock)
		log.Debugf("Got block: %v", b)

		// Find which pool this block belongs to.
		for _, poolUse := range usage {
			if b.CIDR.IsNetOverlap(poolUse.CIDR) {
				log.Debugf("Block CIDR %v belongs to pool %v", b.CIDR, poolUse.Name)
				poolUse.Blocks = append(poolUse.Blocks, BlockUtilization{
					CIDR:      b.CIDR.IPNet,
					Capacity:  b.NumAddresses(),
					Available: len(b.Unallocated),
				})
				break
			}
		}
	}
	return usage, nil
}

// EnsureBlock returns single IPv4/IPv6 IPAM block for a host as specified by the provided BlockArgs.
// If there is no block allocated already for this host, allocate one and return its CIDR.
// Otherwise, return the CIDR of the IPAM block allocated for this host.
func (c ipamClient) EnsureBlock(ctx context.Context, args BlockArgs) (*net.IPNet, *net.IPNet, error) {
	// Determine the hostname to use - prefer the provided hostname if
	// non-nil, otherwise use the hostname reported by os.
	hostname, err := decideHostname(args.Hostname)
	if err != nil {
		return nil, nil, err
	}
	log.Infof("Ensure block for host %s, ipv4 attr %v ipv6 attr %v", hostname, args.HostReservedAttrIPv4s, args.HostReservedAttrIPv6s)

	var v4Net, v6Net *net.IPNet

	if args.HostReservedAttrIPv4s != nil {
		for _, pool := range args.IPv4Pools {
			if pool.IP.To4() == nil {
				return nil, nil, fmt.Errorf("provided IPv4 IPPools list contains one or more IPv6 IPPools")
			}
		}
		v4Net, err = c.ensureBlock(ctx, args.HostReservedAttrIPv4s, args.IPv4Pools, 4, hostname)
		if err != nil {
			log.Errorf("Error ensure IPv4 block: %v", err)
			return nil, nil, err
		}
	}

	if args.HostReservedAttrIPv6s != nil {
		for _, pool := range args.IPv6Pools {
			if pool.IP.To4() != nil {
				return nil, nil, fmt.Errorf("provided IPv6 IPPools list contains one or more IPv4 IPPools")
			}
		}
		v6Net, err = c.ensureBlock(ctx, args.HostReservedAttrIPv6s, args.IPv4Pools, 6, hostname)
		if err != nil {
			log.Errorf("Error ensure IPv6 block: %v", err)
			return nil, nil, err
		}
	}

	return v4Net, v6Net, nil
}

// getMaxPrefixLen returns maximum block size with given host reserved address range.
func getMaxPrefixLen(version int, attrs *HostReservedAttr) (int, error) {
	if attrs == nil {
		if version == 4 {
			return 32, nil
		} else {
			return 128, nil
		}
	}

	// Calculate how may addresses we should reserve in the block.
	numOfReserved := (uint)(attrs.StartOfBlock + attrs.EndOfBlock)

	// For example, with windows OS, IPs x.0, x.1, x.2 and x.<bcast> are
	// reserved. so, minimum 4 IPs are needed for network
	// creation. As a result, don't allow a block size
	// 30, 31, 32 (for IPv4) and 126, 127, 128 (for IPv6).
	var maxPrefixLen int
	if numOfReserved > 0 {
		if version == 4 {
			maxPrefixLen = 32 - bits.Len(numOfReserved)
		} else {
			maxPrefixLen = 128 - bits.Len(numOfReserved)
		}
	}

	if maxPrefixLen <= 0 {
		return 0, fmt.Errorf("HostReservedAttr has wrong parameters")
	}

	return maxPrefixLen, nil
}

func (c ipamClient) ensureBlock(ctx context.Context, rsvdAttr *HostReservedAttr, requestedPools []net.IPNet, version int, host string) (*net.IPNet, error) {
	// This function is similar to autoAssign except it does not allocate ips.

	logCtx := log.WithFields(log.Fields{"host": host})

	logCtx.Info("Looking up existing affinities for host")
	pools, affBlocks, err := c.prepareAffinityBlocksForHost(ctx, requestedPools, version, host, rsvdAttr, v3.IPPoolAllowedUseWorkload)
	if err != nil {
		return nil, err
	}

	logCtx.Debugf("Found %d affine IPv%d blocks for host: %v", len(affBlocks), version, affBlocks)

	// Load the set of reserved IPs/CIDRs.
	reservations, err := c.getReservedIPs(ctx)
	if err != nil {
		return nil, fmt.Errorf("failed to look up reserved IPs: %w", err)
	}

	s := &blockAssignState{
		client:                c,
		version:               version,
		host:                  host,
		pools:                 pools,
		remainingAffineBlocks: affBlocks,
		hostReservedAttr:      rsvdAttr,
		allowNewClaim:         true,
		reservations:          reservations,
	}

	// Ensure a block
	b, _, err := s.findOrClaimBlock(ctx, 0)
	if err != nil {
		log.WithError(err).Error("Failed to ensure a block")
		return nil, err
	}

	blockCIDR := b.Key.(model.BlockKey).CIDR
	logCtx.Infof("Host's block '%s' ", blockCIDR.String())
	return &blockCIDR, nil
}

func (c ipamClient) getReservedIPs(ctx context.Context) (addrFilter, error) {
	reservations, err := c.reservations.List(ctx, options.ListOptions{})
	if err != nil {
		return nil, err
	}
	if len(reservations.Items) == 0 {
		return nilAddrFilter{}, nil
	}
	var cidrs cidrSliceFilter
	for _, r := range reservations.Items {
		for _, cidrStr := range r.Spec.ReservedCIDRs {
			cidrStr = strings.TrimSpace(cidrStr)
			if len(cidrStr) == 0 {
				// Defensive, validation should prevent.
				continue
			}
			_, cidr, err := net.ParseCIDROrIP(cidrStr)
			if err != nil {
				// Defensive, validation should prevent.
				log.WithError(err).WithField("cidr", cidr).Error("Ignoring malformed CIDR in IPReservation.")
			}
			cidrs = append(cidrs, *cidr)
		}
	}
	return cidrs, nil
}
