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compat: populate IPRange in IPAM config when listing networks #28396

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a388d72
compat: populate IPRange in IPAM config when listing networks
crawfordxx Mar 28, 2026
b880c51
compat: fix leaseRangeToIPRangePrefix to account for first-host offset
crawfordxx Mar 31, 2026
7954f92
compat: refactor leaseRangeToIPRangePrefix and add unit tests
crawfordxx Apr 1, 2026
a0fb5cc
compat: use encoding/binary and Masked() check in leaseRangeToIPRange…
crawfordxx Apr 3, 2026
b36b97e
compat: use encoding/binary and Masked() check in leaseRangeToIPRange…
crawfordxx Apr 3, 2026
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54 changes: 53 additions & 1 deletion pkg/api/handlers/compat/networks.go
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Original file line number Diff line number Diff line change
Expand Up @@ -123,7 +123,9 @@ func convertLibpodNetworktoDockerNetwork(runtime *libpod.Runtime, statuses []abi
ipamConfig := dockerNetwork.IPAMConfig{
Subnet: subnet,
Gateway: gateway,
// TODO add range
}
if ipRange, ok := leaseRangeToIPRangePrefix(sub.LeaseRange); ok {
ipamConfig.IPRange = ipRange
}
ipamConfigs = append(ipamConfigs, ipamConfig)
}
Expand Down Expand Up @@ -506,3 +508,53 @@ func Prune(w http.ResponseWriter, r *http.Request) {
}
utils.WriteResponse(w, http.StatusOK, response{NetworksDeleted: prunedNetworks})
}

// leaseRangeToIPRangePrefix converts a LeaseRange back to a CIDR prefix for the Docker
// compat API. This is the reverse of the conversion done in createNetwork, where an
// IPRange CIDR (e.g. "192.168.0.128/25") is expanded to [FirstIP, LastIP] via
// FirstIPInSubnet/LastIPInSubnet. FirstIPInSubnet returns network+1 (first usable host),
// so StartIP is one greater than the network address. LastIPInSubnet returns the broadcast.
// Only succeeds for IPv4 ranges that form a valid aligned CIDR block.
func leaseRangeToIPRangePrefix(lr *nettypes.LeaseRange) (netip.Prefix, bool) {
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@Honny1 Honny1 Mar 31, 2026

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I have a few thoughts on this!

First, this function could be a lot shorter and cleaner. I'm not a huge fan of using raw bitwise operations here; we can make the logic much more elegant and readable. Here is a quick pseudocode mockup of what I mean:

FUNCTION leaseRangeToIPRangePrefix(leaseRange):

    // 1. Initial Validation
    IF leaseRange IS NULL:
        RETURN Null, False
        
    startIP = ParseIPv4(leaseRange.StartIP)
    endIP = ParseIPv4(leaseRange.EndIP)
    
    // Ensure IPs are valid and mathematically start <= end
    IF startIP IS INVALID OR endIP IS INVALID OR startIP > endIP:
        RETURN Null, False

    // 2. Calculate the total number of IPs in the range
    startInt = ConvertTo32BitInteger(startIP)
    endInt = ConvertTo32BitInteger(endIP)
    
    totalIPs = (endInt - startInt) + 1

    // 3. Verify the range size is a valid subnet size
    // A valid subnet size must be a perfect power of 2 (1, 2, 4, 8, 16, etc.)
    // In binary, a perfect power of 2 has exactly one "1" bit.
    IF CountSetBits(totalIPs) != 1:
        RETURN Null, False

    // 4. Calculate the subnet mask / prefix length
    // The number of trailing zeros in the total IPs equals the host bits
    numberOfHostBits = CountTrailingZeros(totalIPs)
    networkPrefixLength = 32 - numberOfHostBits
    
    proposedPrefix = CreateSubnetPrefix(startIP, networkPrefixLength)

    // 5. Verify network boundary alignment
    // The start IP must perfectly match the base network address of the subnet
    IF proposedPrefix DOES NOT EQUAL ApplyNetworkMask(proposedPrefix):
        RETURN Null, False

    // 6. Success
    RETURN proposedPrefix, True

Second, we definitely need to add unit tests for this function.

Lastly (and this isn't a blocker), something in the back of my mind is screaming that this function actually belongs in libnetwork under container-libs. WDYT? @Luap99

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@Luap99 Luap99 Apr 1, 2026

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I am fine with having this code here, I don't think we will need it elsewhere. most of that libnetwork code is going into netavark now so it is not like we could resuse it from there.

if lr == nil || lr.StartIP == nil || lr.EndIP == nil {
return netip.Prefix{}, false
}
start4 := lr.StartIP.To4()
end4 := lr.EndIP.To4()
if start4 == nil || end4 == nil {
// IPv6 not handled: no lossless round-trip without storing the original CIDR
return netip.Prefix{}, false
}
startU := uint32(start4[0])<<24 | uint32(start4[1])<<16 | uint32(start4[2])<<8 | uint32(start4[3])
endU := uint32(end4[0])<<24 | uint32(end4[1])<<16 | uint32(end4[2])<<8 | uint32(end4[3])
if endU < startU {
return netip.Prefix{}, false
}
// For /32, FirstIPInSubnet returns the address unchanged; StartIP == EndIP.
if startU == endU {
startAddr, _ := netip.AddrFromSlice(start4)
return netip.PrefixFrom(startAddr.Unmap(), 32), true
}
// For all other subnets, FirstIPInSubnet increments the network address by 1,
// so recover the network address by subtracting 1 from StartIP.
if startU == 0 {
return netip.Prefix{}, false
}
netU := startU - 1
size := endU - netU + 1
// Verify size is a power of two (required for a valid CIDR block).
if size&(size-1) != 0 {
return netip.Prefix{}, false
}
// Verify the network address is aligned to the block size.
if netU&(size-1) != 0 {
return netip.Prefix{}, false
}
prefixBits := 32
for n := size; n > 1; n >>= 1 {
prefixBits--
}
netBytes := []byte{byte(netU >> 24), byte(netU >> 16), byte(netU >> 8), byte(netU)}
netAddr, _ := netip.AddrFromSlice(netBytes)
return netip.PrefixFrom(netAddr.Unmap(), prefixBits), true
}
6 changes: 6 additions & 0 deletions test/apiv2/35-networks.at
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Expand Up @@ -257,4 +257,10 @@ t POST networks/netcon/connect Container=c1 200 OK
# cleanup
podman network rm -f netcon

# IPRange is populated in IPAM config when a network is created with --ip-range
podman network create --subnet 10.10.61.0/24 --ip-range 10.10.61.128/25 iprange-test
t GET networks/iprange-test 200 \
.IPAM.Config[0].IPRange="10.10.61.128/25"
podman network rm -f iprange-test

# vim: filetype=sh