From 33e0509c5a5ba044b2fea9a70fdafe9079ce3e75 Mon Sep 17 00:00:00 2001
From: 9seconds <nineseconds@yandex.ru>
Date: Wed, 1 Dec 2021 10:51:13 +0300
Subject: [PATCH] Optimize for a fast flush

---
 mtglib/internal/relay/init.go      |  4 ++--
 mtglib/internal/relay/sync_pair.go | 13 ++++++++++++-
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/mtglib/internal/relay/init.go b/mtglib/internal/relay/init.go
index e54ac7a..6278c48 100644
--- a/mtglib/internal/relay/init.go
+++ b/mtglib/internal/relay/init.go
@@ -3,8 +3,8 @@ package relay
 import "time"
 
 const (
-	copyBufferSize   = 32 * 1024
-	writerBufferSize = 2 * copyBufferSize
+	copyBufferSize   = 64 * 1024
+	writerBufferSize = 128 * 1024
 	readTimeout      = 10 * time.Millisecond
 )
 
diff --git a/mtglib/internal/relay/sync_pair.go b/mtglib/internal/relay/sync_pair.go
index 72293e7..500b961 100644
--- a/mtglib/internal/relay/sync_pair.go
+++ b/mtglib/internal/relay/sync_pair.go
@@ -26,6 +26,7 @@ func (s *syncPair) Sync() (int64, error) {
 func (s *syncPair) Read(p []byte) (int, error) {
 	n, err := s.readBlocking(p, false)
 
+	// nothing has been delivered for readTimeout time. Let's flush.
 	if errors.Is(err, os.ErrDeadlineExceeded) {
 		if err := s.Flush(); err != nil {
 			return 0, fmt.Errorf("cannot flush writer hand-side: %w", err)
@@ -41,7 +42,17 @@ func (s *syncPair) Write(p []byte) (int, error) {
 	s.mutex.Lock()
 	defer s.mutex.Unlock()
 
-	return s.writer.Write(p) // nolint: wrapcheck
+	n, err := s.writer.Write(p) // nolint: wrapcheck
+
+	// optimization for a case when we have a small package and want to avoid a
+	// delay in readTimeout. In that case, we assume that peer has finished to
+	// sent a data it wants to send so we can flush without waiting for anything
+	// else.
+	if err == nil && n < copyBufferSize {
+		err = s.writer.Flush()
+	}
+
+	return n, err
 }
 
 func (s *syncPair) Flush() error {