tsnet: add ListenFunnel

This lets a tsnet binary share a server out over Tailscale Funnel.

Signed-off-by: David Crawshaw <crawshaw@tailscale.com>
Signed-off-by: Maisem Ali <maisem@tailscale.com>
Signed-off-by: Shayne Sweeney <shayne@tailscale.com>

ipn/serve_test.go

@@ -0,0 +1,33 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+package ipn
+
+import (
+	"testing"
+
+	"tailscale.com/tailcfg"
+)
+
+func TestCheckFunnelAccess(t *testing.T) {
+	tests := []struct {
+		caps    []string
+		wantErr bool
+	}{
+		{[]string{}, true}, // No "funnel" attribute
+		{[]string{tailcfg.CapabilityWarnFunnelNoInvite}, true},
+		{[]string{tailcfg.CapabilityWarnFunnelNoHTTPS}, true},
+		{[]string{tailcfg.NodeAttrFunnel}, false},
+	}
+	for _, tt := range tests {
+		err := CheckFunnelAccess(tt.caps)
+		switch {
+		case err != nil && tt.wantErr,
+			err == nil && !tt.wantErr:
+			continue
+		case tt.wantErr:
+			t.Fatalf("got no error, want error")
+		case !tt.wantErr:
+			t.Fatalf("got error %v, want no error", err)
+		}
+	}
+}