When the buffer is empty, reset b.off to the beginning of the buffer

to avoid growing unnecessarily.

R=rsc
CC=golang-dev
https://golang.org/cl/176071

diff --git a/src/pkg/bytes/buffer.go b/src/pkg/bytes/buffer.go
index 41838d4907e76dd7f3df5b5e11bd63383a4a30fa..b302b65fa5519130df3e38bf515f647384435769 100644 (file)
--- a/src/pkg/bytes/buffer.go
+++ b/src/pkg/bytes/buffer.go
@@ -84,6 +84,10 @@ func (b *Buffer) resize(n int) {
 // value n is the length of p; err is always nil.
 func (b *Buffer) Write(p []byte) (n int, err os.Error) {
        m := b.Len();
+       // If buffer is empty, reset to recover space.
+       if m == 0 && b.off != 0 {
+               b.Truncate(0)
+       }
        n = len(p);
        if len(b.buf)+n > cap(b.buf) {
                b.resize(n)
@@ -97,6 +101,10 @@ func (b *Buffer) Write(p []byte) (n int, err os.Error) {
 // value n is the length of s; err is always nil.
 func (b *Buffer) WriteString(s string) (n int, err os.Error) {
        m := b.Len();
+       // If buffer is empty, reset to recover space.
+       if m == 0 && b.off != 0 {
+               b.Truncate(0)
+       }
        n = len(s);
        if len(b.buf)+n > cap(b.buf) {
                b.resize(n)
@@ -117,6 +125,10 @@ const MinRead = 512
 // Any error except os.EOF encountered during the read
 // is also returned.
 func (b *Buffer) ReadFrom(r io.Reader) (n int64, err os.Error) {
+       // If buffer is empty, reset to recover space.
+       if b.off >= len(b.buf) {
+               b.Truncate(0)
+       }
        for {
                if cap(b.buf)-len(b.buf) < MinRead {
                        var newBuf []byte;
@@ -157,6 +169,8 @@ func (b *Buffer) WriteTo(w io.Writer) (n int64, err os.Error) {
                        return n, e
                }
        }
+       // Buffer is now empty; reset.
+       b.Truncate(0);
        return;
 }
 
@@ -175,7 +189,9 @@ func (b *Buffer) WriteByte(c byte) os.Error {
 // otherwise it is nil.
 func (b *Buffer) Read(p []byte) (n int, err os.Error) {
        if b.off >= len(b.buf) {
-               return 0, os.EOF
+               // Buffer is empty, reset to recover space.
+               b.Truncate(0);
+               return 0, os.EOF;
        }
        m := b.Len();
        n = len(p);
@@ -194,7 +210,9 @@ func (b *Buffer) Read(p []byte) (n int, err os.Error) {
 // If no byte is available, it returns error os.EOF.
 func (b *Buffer) ReadByte() (c byte, err os.Error) {
        if b.off >= len(b.buf) {
-               return 0, os.EOF
+               // Buffer is empty, reset to recover space.
+               b.Truncate(0);
+               return 0, os.EOF;
        }
        c = b.buf[b.off];
        b.off++;