return byte slice directly from buffer

Updates go-sql-driver#52

buffer.go

@@ -51,35 +51,45 @@ func (b *buffer) fill(need int) (err error) {
  return
 }
 
-// read len(p) bytes
-func (b *buffer) read(p []byte) (err error) {
- need := len(p)
+// 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
+ return
 
- if b.length < need {
+ } 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:])
- need -= b.length
- p = p[b.length:]
-
+ has = b.length
+ need -= has
  b.idx = 0
  b.length = 0
  }
 
- if need >= len(b.buf) {
+ // does the data fit into the buffer?
+ if need < len(b.buf) {
+ err = b.fill(need) // err deferred
+ copy(p[has:has+need], b.buf[b.idx:])
+ b.idx += need
+ b.length -= need
+ return
+
+ } else {
  var n int
- has := 0
- for err == nil && need > has {
+ for err == nil && need > 0 {
  n, err = b.rd.Read(p[has:])
  has += n
+ need -= n
  }
- return
  }
-
- err = b.fill(need) // err deferred
  }
-
- copy(p, b.buf[b.idx:])
- b.idx += need
- b.length -= need
  return
 }

packets.go

@@ -26,15 +26,14 @@ import (
 // Read packet to buffer 'data'
 func (mc *mysqlConn) readPacket() (data []byte, err error) {
  // Read packet header
- data = make([]byte, 4)
- err = mc.buf.read(data)
+ data, err = mc.buf.readNext(4)
  if err != nil {
  errLog.Print(err.Error())
  return nil, driver.ErrBadConn
  }
 
  // Packet Length [24 bit]
- pktLen := uint32(data[0]) | uint32(data[1])<<8 | uint32(data[2])<<16
+ pktLen := int(uint32(data[0]) | uint32(data[1])<<8 | uint32(data[2])<<16)
 
  if pktLen < 1 {
  errLog.Print(errMalformPkt.Error())
@@ -52,8 +51,7 @@ func (mc *mysqlConn) readPacket() (data []byte, err error) {
  mc.sequence++
 
  // Read packet body [pktLen bytes]
- data = make([]byte, pktLen)
- err = mc.buf.read(data)
+ data, err = mc.buf.readNext(pktLen)
  if err == nil {
  if pktLen < maxPacketSize {
  return data, nil