bytes: simplified logic

Also: Avoid potential crash due to reslicing of nil buffer.

R=r
CC=golang-dev
https://golang.org/cl/5556075

diff --git a/src/pkg/bytes/buffer.go b/src/pkg/bytes/buffer.go
index 9d58326a4fb8014756e0873e422986001a2cad48..ccddd95a49a12a24a434c7784f98e8ab526aca96 100644 (file)
--- a/src/pkg/bytes/buffer.go
+++ b/src/pkg/bytes/buffer.go
@@ -139,21 +139,19 @@ func (b *Buffer) ReadFrom(r io.Reader) (n int64, err error) {
                b.Truncate(0)
        }
        for {
-               if cap(b.buf)-len(b.buf) < MinRead {
-                       var newBuf []byte
-                       // can we get space without allocation?
-                       if b.off+cap(b.buf)-len(b.buf) >= MinRead {
-                               // reuse beginning of buffer
-                               newBuf = b.buf[0 : len(b.buf)-b.off]
-                       } else {
-                               // not enough space at end; put space on end
-                               newBuf = makeSlice(2*(cap(b.buf)-b.off) + MinRead)[:len(b.buf)-b.off]
+               if free := cap(b.buf) - len(b.buf); free < MinRead {
+                       // not enough space at end
+                       newBuf := b.buf
+                       if b.off+free < MinRead {
+                               // not enough space using beginning of buffer;
+                               // double buffer capacity
+                               newBuf = makeSlice(2*cap(b.buf) + MinRead)
                                if newBuf == nil {
                                        return n, ErrTooLarge
                                }
                        }
                        copy(newBuf, b.buf[b.off:])
-                       b.buf = newBuf
+                       b.buf = newBuf[:len(b.buf)-b.off]
                        b.off = 0
                }
                m, e := r.Read(b.buf[len(b.buf):cap(b.buf)])