feature/conn25: move addrAssignments to their own file

Updates tailscale/corp#39975

Signed-off-by: Fran Bull <fran@tailscale.com>

feature/conn25/addrAssignments_test.go

@@ -0,0 +1,66 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+package conn25
+
+import (
+	"net/netip"
+	"testing"
+	"time"
+
+	"tailscale.com/tstest"
+)
+
+func TestAssignmentsExpire(t *testing.T) {
+	clock := tstest.NewClock(tstest.ClockOpts{Start: time.Now()})
+	assignments := addrAssignments{clock: clock}
+	as := addrs{
+		dst:     netip.MustParseAddr("0.0.0.1"),
+		magic:   netip.MustParseAddr("0.0.0.2"),
+		transit: netip.MustParseAddr("0.0.0.3"),
+		app:     "a",
+		domain:  "example.com.",
+	}
+	err := assignments.insert(as)
+	if err != nil {
+		t.Fatal(err)
+	}
+	// Time has not passed since the insert, the assignment should be returned.
+	foundAs, ok := assignments.lookupByMagicIP(as.magic)
+	if !ok {
+		t.Fatal("expected to find")
+	}
+	if foundAs.dst != as.dst {
+		t.Fatalf("want %v; got %v", as.dst, foundAs.dst)
+	}
+	// and we cannot insert over the addresses
+	err = assignments.insert(as)
+	if err == nil {
+		t.Fatal("expected an error but got nil")
+	}
+	// After a time greater than the default expiry passes, the assignment should
+	// not be returned.
+	clock.Advance(defaultExpiry * 2)
+	foundAsAfter, okAfter := assignments.lookupByMagicIP(as.magic)
+	if okAfter {
+		t.Fatal("expected not to find (expired)")
+	}
+	if foundAsAfter.isValid() {
+		t.Fatal("expected zero val")
+	}
+	// Now we can reuse the addresses
+	err = assignments.insert(as)
+	if err != nil {
+		t.Fatal(err)
+	}
+	foundAs, ok = assignments.lookupByMagicIP(as.magic)
+	if !ok {
+		t.Fatal("expected to find")
+	}
+	if foundAs.dst != as.dst {
+		t.Fatalf("want %v; got %v", as.dst, foundAs.dst)
+	}
+	if !foundAs.expiresAt.After(clock.Now()) {
+		t.Fatalf("expected foundAs to expire after now")
+	}
+}