feature/taildrop: move rest of Taildrop out of LocalBackend

Updates #12614

Change-Id: If451dec1d796f6a4216fe485975c87f0c62a53e5
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Co-authored-by: Nick Khyl <nickk@tailscale.com>

feature/taildrop/target_test.go

@@ -0,0 +1,73 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package taildrop
+
+import (
+	"fmt"
+	"testing"
+
+	"tailscale.com/ipn"
+	"tailscale.com/ipn/ipnext"
+	"tailscale.com/tailcfg"
+)
+
+func TestFileTargets(t *testing.T) {
+	e := new(Extension)
+
+	_, err := e.FileTargets()
+	if got, want := fmt.Sprint(err), "not connected to the tailnet"; got != want {
+		t.Errorf("before connect: got %q; want %q", got, want)
+	}
+
+	e.nodeBackendForTest = testNodeBackend{peers: nil}
+
+	_, err = e.FileTargets()
+	if got, want := fmt.Sprint(err), "not connected to the tailnet"; got != want {
+		t.Errorf("non-running netmap: got %q; want %q", got, want)
+	}
+
+	e.backendState = ipn.Running
+	_, err = e.FileTargets()
+	if got, want := fmt.Sprint(err), "file sharing not enabled by Tailscale admin"; got != want {
+		t.Errorf("without cap: got %q; want %q", got, want)
+	}
+
+	e.capFileSharing = true
+	got, err := e.FileTargets()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(got) != 0 {
+		t.Fatalf("unexpected %d peers", len(got))
+	}
+
+	var nodeID tailcfg.NodeID = 1234
+	peer := &tailcfg.Node{
+		ID:       nodeID,
+		Hostinfo: (&tailcfg.Hostinfo{OS: "tvOS"}).View(),
+	}
+	e.nodeBackendForTest = testNodeBackend{peers: []tailcfg.NodeView{peer.View()}}
+
+	got, err = e.FileTargets()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(got) != 0 {
+		t.Fatalf("unexpected %d peers", len(got))
+	}
+}
+
+type testNodeBackend struct {
+	ipnext.NodeBackend
+	peers []tailcfg.NodeView
+}
+
+func (t testNodeBackend) AppendMatchingPeers(peers []tailcfg.NodeView, f func(tailcfg.NodeView) bool) []tailcfg.NodeView {
+	for _, p := range t.peers {
+		if f(p) {
+			peers = append(peers, p)
+		}
+	}
+	return peers
+}