drive,ipn/ipnlocal: calculate peer taildrive URLs on-demand

Instead of calculating the PeerAPI URL at the time that we add the peer,
we now calculate it on every access to the peer. This way, if we
initially did not have a shared address family with the peer, but
later do, this allows us to access the peer at that point. This
follows the pattern from other places where we access the peer API,
which also calculate the URL on an as-needed basis.

Additionally, we now show peers as not Available when we can't get
a peer API URL.

Lastly, this moves some of the more frequent verbose Taildrive logging
from [v1] to [v2] level.

Updates #29702

Signed-off-by: Percy Wegmann <percy@tailscale.com>

drive/driveimpl/drive_test.go

@@ -524,7 +524,7 @@ func (s *system) addRemote(name string) string {
 	for name, r := range s.remotes {
 		remotes = append(remotes, &drive.Remote{
 			Name: name,
-			URL:  fmt.Sprintf("http://%s", r.l.Addr()),
+			URL:  func() string { return fmt.Sprintf("http://%s", r.l.Addr()) },
 		})
 	}
 	s.local.fs.SetRemotes(

drive/driveimpl/local_impl.go

@@ -81,7 +81,7 @@ func (s *FileSystemForLocal) SetRemotes(domain string, remotes []*drive.Remote,
 				Name:      remote.Name,
 				Available: remote.Available,
 			},
-			BaseURL:   func() (string, error) { return remote.URL, nil },
+			BaseURL:   func() (string, error) { return remote.URL(), nil },
 			Transport: transport,
 		})
 	}

drive/local.go

@@ -17,7 +17,7 @@ import (
 // Remote represents a remote Taildrive node.
 type Remote struct {
 	Name      string
-	URL       string
+	URL       func() string
 	Available func() bool
 }