all: fix golangci-lint issues (#3064)

hscontrol/dns/extrarecords.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"crypto/sha256"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"os"
 	"sync"
@@ -15,6 +16,9 @@ import (
 	"tailscale.com/util/set"
 )
 
+// ErrPathIsDirectory is returned when a directory path is provided where a file is expected.
+var ErrPathIsDirectory = errors.New("path is a directory, only file is supported")
+
 type ExtraRecordsMan struct {
 	mu      sync.RWMutex
 	records set.Set[tailcfg.DNSRecord]
@@ -39,7 +43,7 @@ func NewExtraRecordsManager(path string) (*ExtraRecordsMan, error) {
 	}
 
 	if fi.IsDir() {
-		return nil, fmt.Errorf("path is a directory, only file is supported: %s", path)
+		return nil, fmt.Errorf("%w: %s", ErrPathIsDirectory, path)
 	}
 
 	records, hash, err := readExtraRecordsFromPath(path)
@@ -85,19 +89,22 @@ func (e *ExtraRecordsMan) Run() {
 				log.Error().Caller().Msgf("file watcher event channel closing")
 				return
 			}
+
 			switch event.Op {
 			case fsnotify.Create, fsnotify.Write, fsnotify.Chmod:
 				log.Trace().Caller().Str("path", event.Name).Str("op", event.Op.String()).Msg("extra records received filewatch event")
+
 				if event.Name != e.path {
 					continue
 				}
+
 				e.updateRecords()
 
 				// If a file is removed or renamed, fsnotify will loose track of it
 				// and not watch it. We will therefore attempt to re-add it with a backoff.
 			case fsnotify.Remove, fsnotify.Rename:
 				_, err := backoff.Retry(context.Background(), func() (struct{}, error) {
-					if _, err := os.Stat(e.path); err != nil {
+					if _, err := os.Stat(e.path); err != nil { //nolint:noinlineerr
 						return struct{}{}, err
 					}
 
@@ -123,6 +130,7 @@ func (e *ExtraRecordsMan) Run() {
 				log.Error().Caller().Msgf("file watcher error channel closing")
 				return
 			}
+
 			log.Error().Caller().Err(err).Msgf("extra records filewatcher returned error: %q", err)
 		}
 	}
@@ -165,6 +173,7 @@ func (e *ExtraRecordsMan) updateRecords() {
 	e.hashes[e.path] = newHash
 
 	log.Trace().Caller().Interface("records", e.records).Msgf("extra records updated from path, count old: %d, new: %d", oldCount, e.records.Len())
+
 	e.updateCh <- e.records.Slice()
 }
 
@@ -183,6 +192,7 @@ func readExtraRecordsFromPath(path string) ([]tailcfg.DNSRecord, [32]byte, error
 	}
 
 	var records []tailcfg.DNSRecord
+
 	err = json.Unmarshal(b, &records)
 	if err != nil {
 		return nil, [32]byte{}, fmt.Errorf("unmarshalling records, content: %q: %w", string(b), err)