net/traffic,ipn/ipnlocal: extract traffic steering utilities (#19682)
The traffic package contains helpers for evaluating traffic steering scores and picking appropriate nodes. These were extracted from ipnlocal.suggestExitNodeUsingTrafficSteering so they can be reused by the new routecheck package to probe exit nodes in priority order. Updates #17366 Updates tailscale/corp#33033 Signed-off-by: Simon Law <sfllaw@tailscale.com>
This commit is contained in:
Simon Law
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// Copyright (c) Tailscale Inc & contributors
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// SPDX-License-Identifier: BSD-3-Clause
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// Package traffic contains helpers for evaluating traffic steering scores and
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// picking appropriate nodes.
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package traffic
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import (
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"cmp"
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"crypto/sha256"
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"encoding/binary"
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"iter"
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"maps"
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"slices"
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"tailscale.com/tailcfg"
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"tailscale.com/util/mak"
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)
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// Score is a node’s traffic score, where any int could be a valid score.
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// A higher traffic score suggests that the client should prefer that peer
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// over one with a lower traffic score.
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type Score int
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// Scores is a memoization cache for the traffic scores of the current node’s peers.
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type Scores struct {
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self tailcfg.NodeID
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hash NodeHasher
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scores map[tailcfg.NodeID]Score
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}
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// ScoresFor returns a new [Scores] cache for the current node’s ID,
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// after scoring the peer nodes and adding these scores to the cache.
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func ScoresFor(self tailcfg.NodeID, peers []tailcfg.NodeView) Scores {
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ss := Scores{
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self: self,
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hash: MakeRendezvousHasher(self),
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}
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ss.ScorePeers(peers)
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return ss
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}
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// IsValid reports whether ss has been initialized with the current node ID.
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func (ss Scores) IsValid() bool {
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return !ss.self.IsZero()
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}
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// Score scores the given peer node and returns it after adding the score to the cache.
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func (ss *Scores) Score(n tailcfg.NodeView) Score {
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id := n.ID()
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if s, ok := ss.scores[id]; ok {
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return s
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}
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var s Score
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if hi := n.Hostinfo(); hi.Valid() {
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if loc := hi.Location(); loc.Valid() {
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s = Score(loc.Priority())
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}
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}
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mak.Set(&ss.scores, id, s)
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return s
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}
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// ScorePeers scores the peer nodes and adds these scores to the cache.
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func (ss *Scores) ScorePeers(peers []tailcfg.NodeView) {
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if len(peers) == 0 {
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return
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}
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if ss.scores == nil {
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ss.scores = make(map[tailcfg.NodeID]Score, len(peers))
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}
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for _, n := range peers {
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ss.Score(n)
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}
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}
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// All returns an iterator over the scores for every peer in the cache.
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// The iteration order is not specified and is not guaranteed to be the same
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// from one call to the next.
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func (ss Scores) All() iter.Seq2[tailcfg.NodeID, Score] {
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return maps.All(ss.scores)
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}
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// SortNodes sorts the slice of nodes in descending order of [Scores.Score],
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// using rendezvous hashing to break ties when both nodes have the same score.
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// After sorting, the zeroth element is the preferred node.
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func (ss Scores) SortNodes(nodes []tailcfg.NodeView) {
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slices.SortFunc(nodes, func(a, b tailcfg.NodeView) int {
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c := cmp.Compare(ss.Score(b), ss.Score(a)) // Highest score first.
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if c == 0 {
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return ss.hash.Compare(b.ID(), a.ID()) // Descending order.
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}
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return c
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})
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}
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// NodeHasher returns a 64-bit hash of a node ID.
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type NodeHasher func(tailcfg.NodeID) uint64
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// MakeRendezvousHasher returns a function that hashes a node ID to a uint64.
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// https://en.wikipedia.org/wiki/Rendezvous_hashing
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func MakeRendezvousHasher(seed tailcfg.NodeID) NodeHasher {
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en := binary.BigEndian
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return func(n tailcfg.NodeID) uint64 {
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var b [16]byte
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en.PutUint64(b[:], uint64(seed))
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en.PutUint64(b[8:], uint64(n))
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v := sha256.Sum256(b[:])
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return en.Uint64(v[:])
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}
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}
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// Compare compares the node ID hashes of peers a and b, using the same convention as [cmp.Compare].
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// Since h is seeded with the current node’s ID, the ordering between a and b will remain stable
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// for this node; but the order may flip for when h is seeded for another node.
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// This function should return zero, if and only if a and b have the same node ID.
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func (h NodeHasher) Compare(a, b tailcfg.NodeID) int {
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c := cmp.Compare(h(a), h(b))
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if c == 0 {
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// In the unlikely event of a hash collision, compare the actual IDs.
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return cmp.Compare(a, b)
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}
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return c
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}
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@@ -0,0 +1,139 @@
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// Copyright (c) Tailscale Inc & contributors
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// SPDX-License-Identifier: BSD-3-Clause
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package traffic_test
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import (
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"maps"
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"testing"
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gocmp "github.com/google/go-cmp/cmp"
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"tailscale.com/net/traffic"
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"tailscale.com/tailcfg"
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)
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// WantScores is a convenience alias for the type of [traffic.Score.scores].
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type wantScores = map[tailcfg.NodeID]traffic.Score
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var scoresCases = []struct {
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name string
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peers []*tailcfg.Node
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want wantScores
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}{
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{
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name: "none",
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peers: nil,
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want: wantScores{},
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},
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{
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name: "no-scores",
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peers: []*tailcfg.Node{
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{ID: 37},
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{ID: 42},
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},
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want: wantScores{
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37: 0,
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42: 0,
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},
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},
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{
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name: "mixed-scores",
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peers: []*tailcfg.Node{
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{ID: 37},
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{
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ID: 42,
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Hostinfo: (&tailcfg.Hostinfo{
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Location: &tailcfg.Location{Priority: 1},
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}).View(),
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},
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},
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want: wantScores{
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37: 0,
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42: 1,
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},
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},
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}
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func TestScoreOne(t *testing.T) {
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for _, tc := range scoresCases {
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if len(tc.peers) == 0 {
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continue
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}
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t.Run(tc.name, func(t *testing.T) {
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selfID := tailcfg.NodeID(1)
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ss := traffic.ScoresFor(selfID, nil)
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for _, n := range tc.peers {
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want := tc.want[n.ID]
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score := ss.Score(n.View())
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if score != want {
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t.Errorf("initial Score for nodeid:%d: score %d, want %d", n.ID, score, want)
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}
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score = ss.Score(n.View())
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if score != want {
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t.Errorf("subsequent Score for nodeid:%d: score %d, want %d", n.ID, score, want)
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}
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}
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got := maps.Collect(ss.All())
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if diff := gocmp.Diff(tc.want, got); diff != "" {
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t.Errorf("-want +got:\n%s", diff)
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}
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})
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}
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}
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func TestScoreMany(t *testing.T) {
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for _, tc := range scoresCases {
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t.Run(tc.name, func(t *testing.T) {
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selfID := tailcfg.NodeID(1)
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var peers []tailcfg.NodeView
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for _, n := range tc.peers {
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peers = append(peers, n.View())
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}
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t.Run("ScoresFor", func(t *testing.T) {
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ss := traffic.ScoresFor(selfID, peers)
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got := maps.Collect(ss.All())
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if diff := gocmp.Diff(tc.want, got); diff != "" {
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t.Errorf("-want +got:\n%s", diff)
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}
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})
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t.Run("ScorePeers", func(t *testing.T) {
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ss := traffic.ScoresFor(selfID, nil)
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ss.ScorePeers(peers)
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got := maps.Collect(ss.All())
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if diff := gocmp.Diff(tc.want, got); diff != "" {
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t.Errorf("-want +got:\n%s", diff)
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}
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})
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})
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}
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}
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func FuzzNodeHasherCompare(f *testing.F) {
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for _, seed := range [][]uint64{
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{0, 0, 0},
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{1, 1, 1},
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{1, 10, 11},
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{1, 11, 10},
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{2, 10, 11},
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} {
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selfID, aID, bID := seed[0], seed[1], seed[2]
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f.Add(selfID, aID, bID)
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}
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f.Fuzz(func(t *testing.T, selfID, aID, bID uint64) {
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t.Logf("selfID %d, aID %d, bID %d", selfID, aID, bID)
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h := traffic.MakeRendezvousHasher(tailcfg.NodeID(selfID))
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a, b := tailcfg.NodeID(aID), tailcfg.NodeID(bID)
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c := h.Compare(a, b)
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if c == 0 && a != b {
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t.Fatalf("got %d: expected different hashes because a ≠ b, ", c)
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}
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if cc := h.Compare(a, b); c != cc {
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t.Fatalf("c %d, cc %d: expected matching values", c, cc)
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}
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if d := h.Compare(b, a); c != -d {
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t.Fatalf("c %d, d %d: expected inverse values", c, d)
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}
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})
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}
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