optimize readPacket (#1705)

Avoid unnecessary allocation.

Author: methane

buffer.go

@@ -42,6 +42,11 @@ func (b *buffer) busy() bool{
 returnlen(b.buf) >0
 }
 
+// len returns how many bytes in the read buffer.
+func (b*buffer) len() int{
+returnlen(b.buf)
+}
+
 // fill reads into the read buffer until at least _need_ bytes are in it.
 func (b*buffer) fill(needint, rreaderFunc) error{
 // we'll move the contents of the current buffer to dest before filling it.
@@ -86,17 +91,10 @@ func (b *buffer) fill(need int, r readerFunc) error{
 
 // returns next N bytes from buffer.
 // The returned slice is only guaranteed to be valid until the next read
-func (b*buffer) readNext(needint, rreaderFunc) ([]byte, error){
-iflen(b.buf) <need{
-// refill
-iferr:=b.fill(need, r); err!=nil{
-returnnil, err
- }
- }
-
-data:=b.buf[:need]
+func (b*buffer) readNext(needint) []byte{
+data:=b.buf[:need:need]
 b.buf=b.buf[need:]
-returndata, nil
+returndata
 }
 
 // takeBuffer returns a buffer with the requested size.

compress.go

@@ -84,26 +84,26 @@ func (c *compIO) reset(){
 c.buff.Reset()
 }
 
-func (c*compIO) readNext(needint, rreaderFunc) ([]byte, error){
+func (c*compIO) readNext(needint) ([]byte, error){
 forc.buff.Len() <need{
-iferr:=c.readCompressedPacket(r); err!=nil{
+iferr:=c.readCompressedPacket(); err!=nil{
 returnnil, err
  }
  }
 data:=c.buff.Next(need)
 returndata[:need:need], nil// prevent caller writes into c.buff
 }
 
-func (c*compIO) readCompressedPacket(rreaderFunc) error{
-header, err:=c.mc.buf.readNext(7, r) // size of compressed header
+func (c*compIO) readCompressedPacket() error{
+header, err:=c.mc.readNext(7)
 iferr!=nil{
 returnerr
  }
 _=header[6] // bounds check hint to compiler; guaranteed by readNext
 
 // compressed header structure
 comprLength:=getUint24(header[0:3])
-compressionSequence:=uint8(header[3])
+compressionSequence:=header[3]
 uncompressedLength:=getUint24(header[4:7])
 ifdebug{
 fmt.Printf("uncompress cmplen=%v uncomplen=%v pkt_cmp_seq=%v expected_cmp_seq=%v\n",
@@ -120,7 +120,7 @@ func (c *compIO) readCompressedPacket(r readerFunc) error{
 c.mc.sequence=compressionSequence+1
 c.mc.compressSequence=c.mc.sequence
 
-comprData, err:=c.mc.buf.readNext(comprLength, r)
+comprData, err:=c.mc.readNext(comprLength)
 iferr!=nil{
 returnerr
  }

packets.go

@@ -25,19 +25,30 @@ import (
 // https://dev.mysql.com/doc/dev/mysql-server/latest/PAGE_PROTOCOL.html
 // https://mariadb.com/kb/en/clientserver-protocol/
 
+// read n bytes from mc.buf
+func (mc*mysqlConn) readNext(nint) ([]byte, error){
+ifmc.buf.len() <n{
+err:=mc.buf.fill(n, mc.readWithTimeout)
+iferr!=nil{
+returnnil, err
+ }
+ }
+returnmc.buf.readNext(n), nil
+}
+
 // Read packet to buffer 'data'
 func (mc*mysqlConn) readPacket() ([]byte, error){
 varprevData []byte
 invalidSequence:=false
 
-readNext:=mc.buf.readNext
+readNext:=mc.readNext
 ifmc.compress{
 readNext=mc.compIO.readNext
  }
 
 for{
 // read packet header
-data, err:=readNext(4, mc.readWithTimeout)
+data, err:=readNext(4)
 iferr!=nil{
 mc.close()
 ifcerr:=mc.canceled.Value(); cerr!=nil{
@@ -85,7 +96,7 @@ func (mc *mysqlConn) readPacket() ([]byte, error){
  }
 
 // read packet body [pktLen bytes]
-data, err=readNext(pktLen, mc.readWithTimeout)
+data, err=readNext(pktLen)
 iferr!=nil{
 mc.close()
 ifcerr:=mc.canceled.Value(); cerr!=nil{