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tunnel/hints.go
| 1 | package main |
| 2 | |
| 3 | import ( |
| 4 | "net/netip" |
| 5 | "sync" |
| 6 | "time" |
| 7 | ) |
| 8 | |
| 9 | // HINT (the design plan, sections 2 and 5): a device tells its node which source addresses just completed authenticated calls to it. They get the |
| 10 | // slice of the device's stream cap that anonymous sources cannot use (policy node_limits.label_hint_slice), so a flood from many addresses cannot lock |
| 11 | // out the one that is ChatGPT. The table is memory only, an address stays good for hint_ttl_s after the last HINT that named it, a device can mark |
| 12 | // at most hint_addresses_per_label addresses (the oldest go first), and a mark is filed under the host the control plane's answer gave that connection: |
| 13 | // a device cannot mark an address for any host but its own. |
| 14 | |
| 15 | type hintSet struct { |
| 16 | until map[netip.Addr]time.Time |
| 17 | } |
| 18 | |
| 19 | // hintTable is the node's record of the addresses devices marked good, per device host. |
| 20 | type hintTable struct { |
| 21 | clk clock |
| 22 | ttl time.Duration |
| 23 | cap int |
| 24 | |
| 25 | mu sync.Mutex |
| 26 | hosts map[string]*hintSet |
| 27 | } |
| 28 | |
| 29 | func newHintTable(clk clock, ttl time.Duration, perLabel int) *hintTable { |
| 30 | return &hintTable{clk: clk, ttl: ttl, cap: perLabel, hosts: map[string]*hintSet{}} |
| 31 | } |
| 32 | |
| 33 | // mark records the addresses (never more than the protocol's list) as good for host from now until the TTL. |
| 34 | func (h *hintTable) mark(host string, addrs []netip.Addr) { |
| 35 | now := h.clk.Now() |
| 36 | h.mu.Lock() |
| 37 | defer h.mu.Unlock() |
| 38 | set := h.hosts[host] |
| 39 | if set == nil { |
| 40 | set = &hintSet{until: map[netip.Addr]time.Time{}} |
| 41 | h.hosts[host] = set |
| 42 | } |
| 43 | for _, a := range addrs { |
| 44 | set.until[a.WithZone("").Unmap()] = now.Add(h.ttl) |
| 45 | } |
| 46 | if len(set.until) <= h.cap { |
| 47 | return |
| 48 | } |
| 49 | for a, t := range set.until { // expired first |
| 50 | if !now.Before(t) { |
| 51 | delete(set.until, a) |
| 52 | } |
| 53 | } |
| 54 | for len(set.until) > h.cap { // then the ones that will expire soonest, which are the ones marked longest ago |
| 55 | var oldest netip.Addr |
| 56 | var first time.Time |
| 57 | for a, t := range set.until { |
| 58 | if first.IsZero() || t.Before(first) { |
| 59 | oldest, first = a, t |
| 60 | } |
| 61 | } |
| 62 | delete(set.until, oldest) |
| 63 | } |
| 64 | } |
| 65 | |
| 66 | // good reports whether the device of host marked addr and the mark has not expired. |
| 67 | func (h *hintTable) good(host string, addr netip.Addr) bool { |
| 68 | now := h.clk.Now() |
| 69 | addr = addr.WithZone("").Unmap() |
| 70 | h.mu.Lock() |
| 71 | defer h.mu.Unlock() |
| 72 | set := h.hosts[host] |
| 73 | if set == nil { |
| 74 | return false |
| 75 | } |
| 76 | t, ok := set.until[addr] |
| 77 | return ok && now.Before(t) |
| 78 | } |
| 79 | |
| 80 | // goodAnywhere reports whether the device of ANY host marked addr and the mark has not expired. |
| 81 | func (h *hintTable) goodAnywhere(addr netip.Addr) bool { |
| 82 | now := h.clk.Now() |
| 83 | addr = addr.WithZone("").Unmap() |
| 84 | h.mu.Lock() |
| 85 | defer h.mu.Unlock() |
| 86 | for _, set := range h.hosts { |
| 87 | if t, ok := set.until[addr]; ok && now.Before(t) { |
| 88 | return true |
| 89 | } |
| 90 | } |
| 91 | return false |
| 92 | } |
| 93 | |
| 94 | // Sweep forgets what expired (a background task calls it). |
| 95 | func (h *hintTable) Sweep() { |
| 96 | now := h.clk.Now() |
| 97 | h.mu.Lock() |
| 98 | defer h.mu.Unlock() |
| 99 | for host, set := range h.hosts { |
| 100 | for a, t := range set.until { |
| 101 | if !now.Before(t) { |
| 102 | delete(set.until, a) |
| 103 | } |
| 104 | } |
| 105 | if len(set.until) == 0 { |
| 106 | delete(h.hosts, host) |
| 107 | } |
| 108 | } |
| 109 | } |
| 110 | |
| 111 | // size is the number of addresses held, for the metrics (an aggregate: never per device). |
| 112 | func (h *hintTable) size() int { |
| 113 | h.mu.Lock() |
| 114 | defer h.mu.Unlock() |
| 115 | n := 0 |
| 116 | for _, set := range h.hosts { |
| 117 | n += len(set.until) |
| 118 | } |
| 119 | return n |
| 120 | } |