cmd/natc: allow specifying the tsnet state dir

Which can make operating the service more convenient.
It makes sense to put the cluster state with this if specified, so
rearrange the logic to handle that.

Updates #14667

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

cmd/natc/ippool/consensusippool.go

@@ -10,8 +10,6 @@ import (
 	"fmt"
 	"log"
 	"net/netip"
-	"os"
-	"path/filepath"
 	"time"
 
 	"github.com/hashicorp/raft"
@@ -155,11 +153,7 @@ func (ipp *ConsensusIPPool) domainLookup(from tailcfg.NodeID, addr netip.Addr) (
 func (ipp *ConsensusIPPool) StartConsensus(ctx context.Context, ts *tsnet.Server, clusterTag string, clusterStateDir string) error {
 	cfg := tsconsensus.DefaultConfig()
 	cfg.ServeDebugMonitor = true
-	var err error
-	cfg.StateDirPath, err = getStatePath(clusterStateDir)
-	if err != nil {
-		return err
-	}
+	cfg.StateDirPath = clusterStateDir
 	cns, err := tsconsensus.Start(ctx, ts, ipp, clusterTag, cfg)
 	if err != nil {
 		return err
@@ -211,30 +205,6 @@ func (ps *consensusPerPeerState) unusedIPV4(ipset *netipx.IPSet, reuseDeadline t
 	return netip.Addr{}, false, "", errors.New("ip pool exhausted")
 }
 
-func getStatePath(pathFromFlag string) (string, error) {
-	var dirPath string
-	if pathFromFlag != "" {
-		dirPath = pathFromFlag
-	} else {
-		confDir, err := os.UserConfigDir()
-		if err != nil {
-			return "", err
-		}
-		dirPath = filepath.Join(confDir, "nat-connector-cluster-state")
-	}
-
-	if err := os.MkdirAll(dirPath, 0700); err != nil {
-		return "", err
-	}
-	if fi, err := os.Stat(dirPath); err != nil {
-		return "", err
-	} else if !fi.IsDir() {
-		return "", fmt.Errorf("%v is not a directory", dirPath)
-	}
-
-	return dirPath, nil
-}
-
 // isCloseToExpiry returns true if the lastUsed and now times are more than
 // half the lifetime apart
 func isCloseToExpiry(lastUsed, now time.Time, lifetime time.Duration) bool {