Make the network and broadcast address reservation optional and editable

[GeertJohan]

Every prefix reserves its network and (IPv4) broadcast address at creation (the FIXME in newPrefix). For prefixes used as routed pools, where no L2 semantics apply, this wastes addresses: a /30 yields 2 usable instead of 4.

• NewPrefix accepts options; WithoutNetworkAndBroadcastReservation() creates a prefix whose network and broadcast address are allocatable.
• SetNetworkAndBroadcastReservation(ctx, cidr, reserved) edits the flag on an existing prefix: unreserving is always possible, re-reserving fails while either address is allocated.
• The flag persists through all storages (prefixJSON) and gob; decoding data from before this field defaults to the previous behavior (reserved).
• hasIPs() and the child prefix release check now account for the flag, so an unreserved prefix with a single allocation cannot be deleted. The child release check previously allowed len(ips) up to 2 regardless of address family; it now uses hasIPs().

Used AI-Tools ✨

• Claude Fable 5

Noteworthy

• The gob encoding gains one trailing field. Old encodings decode fine with this version (the missing field defaults to the previous behavior, reserved). Older versions also still decode new encodings, ignoring the trailing field. The one unsafe pattern is a mixed-version round trip: an older go-ipam re-encoding a prefix drops the flag, so a prefix created without the reservation would afterwards read as reserved while its network and broadcast address remain allocatable. Gob-persisting deployments should not run mixed versions against the same data.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 36.33441% with 198 lines in your changes missing coverage. Please review.
✅ Project coverage is 33.73%. Comparing base (7636b1b) to head (3a86aa6).

Files with missing lines	Patch %	Lines
api/v1/ipam.pb.go	0.00%	140 Missing ⚠️
prefix.go	75.96%	14 Missing and 11 partials ⚠️
api/v1/apiv1connect/ipam.connect.go	0.00%	21 Missing ⚠️
cmd/client/client.go	0.00%	6 Missing ⚠️
pkg/service/ipam-service.go	78.57%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #199      +/-   ##
==========================================
+ Coverage   33.46%   33.73%   +0.27%     
==========================================
  Files          17       17              
  Lines        3156     3338     +182     
==========================================
+ Hits         1056     1126      +70     
- Misses       1878     1978     +100     
- Partials      222      234      +12     

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[majst01]

GRPC Service needs this option to be exposed as well

[GeertJohan]

Changed the naming, I think it's more friendly to read / self-documenting now.

[GeertJohan]

And implemented gRPC :)

[majst01]

/ok-to-build

[majst01]

Usage reporting needs also adoption

[GeertJohan]

@majst01 Added this. Note that the diff changes the meaning of Usage.AvailableIPs and Usage.AcquiredIPs. This could be considered a breaking change by users who depended on AcquiredIPs giving 2 on a fresh/"unused" IPv4 prefix. (Hyrum's law...)
Even though it's not a breaking API change, we could consider a major version bump of go-ipam to notify users of the change. Alternatively, we could revert the behavior of AcquiredIPs, but that feels backwards/wrong.

[majst01]

/ok-to-build