package bart provides a Balanced-Routing-Table (BART).
BART is balanced in terms of memory usage and lookup time for the longest-prefix match.
BART is a multibit-trie with fixed stride length of 8 bits, using a fast mapping function (taken from the ART algorithm) to map the 256 prefixes in each level node to form a complete-binary-tree.
This complete binary tree is implemented with popcount compressed sparse arrays together with path compression. This reduces storage consumption by almost two orders of magnitude in comparison to ART, with even better lookup times for the longest prefix match.
The BART algorithm is based on fixed size bit vectors and precalculated lookup tables. The lookup is performed entirely by fast, cache-friendly bitmask operations, which in modern CPUs are performed by advanced bit manipulation instruction sets (POPCNT, LZCNT, TZCNT, ...).
The algorithm was specially developed so that it can always work with a fixed length of 256 bits. This means that the bitset fit very well in a cache line and that loops over the bitset in hot paths can be accelerated by loop unrolling, e.g.
func (b *BitSet256) Intersection(c *BitSet256) (bs BitSet256) {
bs[0] = b[0] & c[0]
bs[1] = b[1] & c[1]
bs[2] = b[2] & c[2]
bs[3] = b[3] & c[3]
return
}The BART algorithm is also excellent for determining whether two tables contain overlapping IP addresses, just in a few nanoseconds.
A bart.Lite wrapper is included, this is ideal for simple IP
ACLs (access-control-lists) with plain true/false results and no payload.
func ExampleLite_Contains() {
lite := new(bart.Lite)
// Insert some prefixes
prefixes := []string{
"192.168.0.0/16",
"192.168.1.0/24",
"2001:7c0:3100::/40",
"2001:7c0:3100:1::/64",
"fc00::/7",
}
for _, s := range prefixes {
pfx := netip.MustParsePrefix(s)
lite.Insert(pfx)
}
// Test some IP addresses for black/whitelist containment
ips := []string{
"192.168.1.100", // must match
"192.168.2.1", // must match
"2001:7c0:3100:1::1", // must match
"2001:7c0:3100:2::1", // must match
"fc00::1", // must match
//
"172.16.0.1", // must NOT match
"2003:dead:beef::1", // must NOT match
}
for _, s := range ips {
ip := netip.MustParseAddr(s)
ok := lite.Contains(ip)
fmt.Printf("%-20s is contained: %t\n", ip, ok)
}
// Output:
// 192.168.1.100 is contained: true
// 192.168.2.1 is contained: true
// 2001:7c0:3100:1::1 is contained: true
// 2001:7c0:3100:2::1 is contained: true
// fc00::1 is contained: true
// 172.16.0.1 is contained: false
// 2003:dead:beef::1 is contained: false
}From release v0.18.x on, bart requires at least go1.23, the iter.Seq2[netip.Prefix, V] types for iterators
are used. The lock-free versions of insert, update and delete are added, but still experimentell.
import "github.com/gaissmai/bart"
type Table[V any] struct {
// Has unexported fields.
}
// Table is an IPv4 and IPv6 routing table with payload V. The zero value is
// ready to use.
// The Table is safe for concurrent readers but not for concurrent readers
// and/or writers. Either the update operations must be protected by an
// external lock mechanism or the various ...Persist functions must be used
// which return a modified routing table by leaving the original unchanged
// A Table must not be copied by value.
func (t *Table[V]) Contains(ip netip.Addr) bool
func (t *Table[V]) Lookup(ip netip.Addr) (val V, ok bool)
func (t *Table[V]) LookupPrefix(pfx netip.Prefix) (val V, ok bool)
func (t *Table[V]) LookupPrefixLPM(pfx netip.Prefix) (lpm netip.Prefix, val V, ok bool)
func (t *Table[V]) Insert(pfx netip.Prefix, val V)
func (t *Table[V]) Delete(pfx netip.Prefix)
func (t *Table[V]) Update(pfx netip.Prefix, cb func(val V, ok bool) V) (newVal V)
func (t *Table[V]) InsertPersist(pfx netip.Prefix, val V) *Table[V]
func (t *Table[V]) DeletePersist(pfx netip.Prefix) *Table[V]
func (t *Table[V]) UpdatePersist(pfx netip.Prefix, cb func(val V, ok bool) V) (pt *Table[V], newVal V)
func (t *Table[V]) Get(pfx netip.Prefix) (val V, ok bool)
func (t *Table[V]) GetAndDelete(pfx netip.Prefix) (val V, ok bool)
func (t *Table[V]) GetAndDeletePersist(pfx netip.Prefix) (pt *Table[V], val V, ok bool)
func (t *Table[V]) Union(o *Table[V])
func (t *Table[V]) Clone() *Table[V]
func (t *Table[V]) OverlapsPrefix(pfx netip.Prefix) bool
func (t *Table[V]) Overlaps(o *Table[V]) bool
func (t *Table[V]) Overlaps4(o *Table[V]) bool
func (t *Table[V]) Overlaps6(o *Table[V]) bool
func (t *Table[V]) Subnets(pfx netip.Prefix) iter.Seq2[netip.Prefix, V]
func (t *Table[V]) Supernets(pfx netip.Prefix) iter.Seq2[netip.Prefix, V]
func (t *Table[V]) All() iter.Seq2[netip.Prefix, V]
func (t *Table[V]) All4() iter.Seq2[netip.Prefix, V]
func (t *Table[V]) All6() iter.Seq2[netip.Prefix, V]
func (t *Table[V]) AllSorted() iter.Seq2[netip.Prefix, V]
func (t *Table[V]) AllSorted4() iter.Seq2[netip.Prefix, V]
func (t *Table[V]) AllSorted6() iter.Seq2[netip.Prefix, V]
func (t *Table[V]) Size() int
func (t *Table[V]) Size4() int
func (t *Table[V]) Size6() int
func (t *Table[V]) String() string
func (t *Table[V]) Fprint(w io.Writer) error
func (t *Table[V]) MarshalText() ([]byte, error)
func (t *Table[V]) MarshalJSON() ([]byte, error)
func (t *Table[V]) DumpList4() []DumpListNode[V]
func (t *Table[V]) DumpList6() []DumpListNode[V]Please see the extensive benchmarks comparing bart with other IP routing table implementations.
Just a teaser, Contains and Lookup against the Tier1 full Internet routing table with
random IP address probes:
goos: linux
goarch: amd64
pkg: github.com/gaissmai/bart
cpu: Intel(R) Core(TM) i5-8250U CPU @ 1.60GHz
BenchmarkFullMatch4/Contains 81672672 14.58 ns/op
BenchmarkFullMatch6/Contains 94038417 12.43 ns/op
BenchmarkFullMiss4/Contains 259998007 4.61 ns/op
BenchmarkFullMiss6/Contains 250340162 4.81 ns/op
goos: linux
goarch: amd64
pkg: github.com/gaissmai/bart
cpu: Intel(R) Core(TM) i5-8250U CPU @ 1.60GHz
BenchmarkFullMatch4/Lookup 52725478 22.65 ns/op
BenchmarkFullMatch6/Lookup 89137046 13.92 ns/op
BenchmarkFullMiss4/Lookup 181541365 6.60 ns/op
BenchmarkFullMiss6/Lookup 168788408 7.07 ns/op
The package is currently released as a pre-v1 version, which gives the author the freedom to break backward compatibility to help improve the API as he learns which initial design decisions would need to be revisited to better support the use cases that the library solves for.
These occurrences are expected to be rare in frequency and the API is already quite stable.
Please open an issue for discussion before sending a pull request.
Standing on the shoulders of giants.
Credits for many inspirations go to
- the clever guys at tailscale,
- to Daniel Lemire for his inspiring blog,
- to Donald E. Knuth for the ART routing algorithm and
- to Yoichi Hariguchi who deciphered it for us mere mortals
And last but not least to the Go team who do a wonderful job!
MIT