From 277aa9c67415b9b76ab17daea583b51f8560a6a5 Mon Sep 17 00:00:00 2001
From: unclejack <unclejacksons@gmail.com>
Date: Wed, 17 Sep 2014 16:50:56 +0300
Subject: [PATCH] stdcopy: improve perf by avoiding buffer growth

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
---
 pkg/stdcopy/stdcopy.go | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/pkg/stdcopy/stdcopy.go b/pkg/stdcopy/stdcopy.go
index b50c31dd49..79e15bc852 100644
--- a/pkg/stdcopy/stdcopy.go
+++ b/pkg/stdcopy/stdcopy.go
@@ -29,14 +29,22 @@ type StdWriter struct {
 }
 
 func (w *StdWriter) Write(buf []byte) (n int, err error) {
+	var n1, n2 int
 	if w == nil || w.Writer == nil {
 		return 0, errors.New("Writer not instanciated")
 	}
 	binary.BigEndian.PutUint32(w.prefix[4:], uint32(len(buf)))
-	buf = append(w.prefix[:], buf...)
-
-	n, err = w.Writer.Write(buf)
-	return n - StdWriterPrefixLen, err
+	n1, err = w.Writer.Write(w.prefix[:])
+	if err != nil {
+		n = n1 - StdWriterPrefixLen
+	} else {
+		n2, err = w.Writer.Write(buf)
+		n = n1 + n2 - StdWriterPrefixLen
+	}
+	if n < 0 {
+		n = 0
+	}
+	return
 }
 
 // NewStdWriter instanciates a new Writer.