refactor: drop ensurewriter wrapper (#42062) (#42174)

* refactor: drop ensurewriter wrapper

stdlib properly handles EAGAIN and EINTR so there is no
need for the extra wrapper and duplicate handling

* Update util.go

* Update util.go

* Update util.go

* Update util.go

(cherry picked from commit 95a32ed)

Co-authored-by: kruskall <99559985+kruskall@users.noreply.github.com>

libbeat/statestore/backend/memlog/diskstore.go

@@ -201,7 +201,7 @@ func (s *diskstore) tryOpenLog() error {
 	ok = true
 	s.logNeedsTruncate = false
 	s.logFile = f
-	s.logBuf = bufio.NewWriterSize(&ensureWriter{s.logFile}, s.bufferSize)
+	s.logBuf = bufio.NewWriterSize(s.logFile, s.bufferSize)
 	return nil
 }
 
@@ -346,7 +346,7 @@ func (s *diskstore) checkpointTmpFile(tempfile string, states map[string]entry)
 		f.Close()
 	})
 
-	writer := bufio.NewWriterSize(&ensureWriter{f}, s.bufferSize)
+	writer := bufio.NewWriterSize(f, s.bufferSize)
 	enc := newJSONEncoder(writer)
 	if _, err = writer.Write([]byte{'['}); err != nil {
 		return "", err
@@ -650,7 +650,7 @@ func writeMetaFile(home string, mode os.FileMode) error {
 		f.Close()
 	})
 
-	enc := newJSONEncoder(&ensureWriter{f})
+	enc := newJSONEncoder(f)
 	err = enc.Encode(storeMeta{
 		Version: storeVersion,
 	})

libbeat/statestore/backend/memlog/util.go

@@ -18,26 +18,13 @@
 package memlog
 
 import (
+	"errors"
 	"io"
 	"os"
 	"runtime"
 	"syscall"
 )
 
-// ensureWriter writes the buffer to the underlying writer
-// for as long as w returns a retryable error (e.g. EAGAIN)
-// or the input buffer has been exhausted.
-//
-// XXX: this code was written and tested with go1.13 and go1.14, which does not
-// handled EINTR. Some users report EINTR getting triggered more often in
-// go1.14 due to changes in the signal handling for implementing
-// preemption.
-// In future versions EINTR will be handled by go for us.
-// See: https://github.com/golang/go/issues/38033
-type ensureWriter struct {
-	w io.Writer
-}
-
 // countWriter keeps track of the amount of bytes written over time.
 type countWriter struct {
 	n uint64
@@ -50,20 +37,10 @@ func (c *countWriter) Write(p []byte) (int, error) {
 	return n, err
 }
 
-func (e *ensureWriter) Write(p []byte) (int, error) {
-	var N int
-	for len(p) > 0 {
-		n, err := e.w.Write(p)
-		N, p = N+n, p[n:]
-		if err != nil && !isRetryErr(err) {
-			return N, err
-		}
-	}
-	return N, nil
-}
+var _ = isRetryErr
 
 func isRetryErr(err error) bool {
-	return err == syscall.EINTR || err == syscall.EAGAIN
+	return errors.Is(err, syscall.EINTR) || errors.Is(err, syscall.EAGAIN)
 }
 
 // trySyncPath provides a best-effort fsync on path (directory). The fsync is required by some
@@ -75,6 +52,7 @@ func trySyncPath(path string) {
 		return // ignore error, sync on dir must not be necessarily supported by the FS
 	}
 	defer f.Close()
+	//nolint:errcheck // ignore error
 	syncFile(f)
 }