Grow buffer instead of using a tmp slice

buffer.go

@@ -9,13 +9,9 @@
 
 package mysql
 
-import (
- "io"
-)
+import "io"
 
-const (
- defaultBufSize = 4096
-)
+const defaultBufSize = 4096
 
 type buffer struct {
  buf []byte
@@ -38,6 +34,11 @@ func (b *buffer) fill(need int) (err error) {
  copy(b.buf[0:b.length], b.buf[b.idx:])
  }
 
+ // grow buffer if necessary
+ if need > len(b.buf) {
+ b.grow(need)
+ }
+
  b.idx = 0
 
  var n int
@@ -54,48 +55,32 @@ func (b *buffer) fill(need int) (err error) {
  return
 }
 
-// returns next N bytes from buffer.
-// The returned slice is only guaranteed to be valid until the next read
-func (b *buffer) readNext(need int) (p []byte, err error) {
- // return slice from buffer if possible
- if b.length >= need {
- p = b.buf[b.idx : b.idx+need]
- b.idx += need
- b.length -= need
+// credit for this code snippet goes to Maxim Khitrov
+// https://groups.google.com/forum/#!topic/golang-nuts/ETbw1ECDgRs
+func (b *buffer) grow(size int) {
+ if size > 2*cap(b.buf) {
+ newBuf := make([]byte, size)
+ copy(newBuf, b.buf)
+ b.buf = newBuf
  return
-
  } else {
-
- // does the data fit into the buffer?
- if need < len(b.buf) {
- // refill
- err = b.fill(need) // err deferred
- p = b.buf[:need]
- b.idx += need
- b.length -= need
- return
-
- } else {
- p = make([]byte, need)
- has := 0
-
- // copy data that is already in the buffer
- if b.length > 0 {
- copy(p[0:b.length], b.buf[b.idx:])
- has = b.length
- need -= has
- b.idx = 0
- b.length = 0
- }
-
- // read rest directly into the new slice
- var n int
- for err == nil && need > 0 {
- n, err = b.rd.Read(p[has:])
- has += n
- need -= n
- }
+ for cap(b.buf) < size {
+ b.buf = append(b.buf[:cap(b.buf)], 0)
  }
+ b.buf = b.buf[:cap(b.buf)]
+ }
+}
+
+// returns next N bytes from buffer.
+// The returned slice is only guaranteed to be valid until the next read
+func (b *buffer) readNext(need int) (p []byte, err error) {
+ if b.length < need {
+ // refill
+ err = b.fill(need) // err deferred
  }
+
+ p = b.buf[b.idx : b.idx+need]
+ b.idx += need
+ b.length -= need
  return
 }