Revert "GODRIVER-3533 Optimize value reader and writer (#2022)"

This reverts commit 8c453d2.

Author: prestonvasquez

bson/marshal.go

@@ -74,10 +74,7 @@ func Marshal(val interface{}) ([]byte, error) {
 		}
 	}()
 	sw.Reset()
-
-	vw := getDocumentWriter(sw)
-	defer putDocumentWriter(vw)
-
+	vw := NewDocumentWriter(sw)
 	enc := encPool.Get().(*Encoder)
 	defer encPool.Put(enc)
 	enc.Reset(vw)

bson/unmarshal.go

@@ -42,9 +42,7 @@ type ValueUnmarshaler interface {
 // When unmarshaling BSON, if the BSON value is null and the Go value is a
 // pointer, the pointer is set to nil without calling UnmarshalBSONValue.
 func Unmarshal(data []byte, val interface{}) error {
-	vr := getDocumentReader(bytes.NewReader(data))
-	defer putDocumentReader(vr)
-
+	vr := newDocumentReader(bytes.NewReader(data))
 	if l, err := vr.peekLength(); err != nil {
 		return err
 	} else if int(l) != len(data) {

bson/value_reader.go

@@ -13,7 +13,6 @@ import (
 	"fmt"
 	"io"
 	"math"
-	"sync"
 )
 
 var _ ValueReader = &valueReader{}
@@ -30,20 +29,6 @@ type vrState struct {
 	end   int64
 }
 
-var bufioReaderPool = sync.Pool{
-	New: func() interface{} {
-		return bufio.NewReader(nil)
-	},
-}
-
-var vrPool = sync.Pool{
-	New: func() interface{} {
-		return &valueReader{
-			stack: make([]vrState, 1, 5),
-		}
-	},
-}
-
 // valueReader is for reading BSON values.
 type valueReader struct {
 	r      *bufio.Reader
@@ -53,33 +38,6 @@ type valueReader struct {
 	frame int64
 }
 
-func getDocumentReader(r io.Reader) *valueReader {
-	vr := vrPool.Get().(*valueReader)
-
-	vr.offset = 0
-	vr.frame = 0
-
-	vr.stack = vr.stack[:1]
-	vr.stack[0] = vrState{mode: mTopLevel}
-
-	br := bufioReaderPool.Get().(*bufio.Reader)
-	br.Reset(r)
-	vr.r = br
-
-	return vr
-}
-
-func putDocumentReader(vr *valueReader) {
-	if vr == nil {
-		return
-	}
-
-	bufioReaderPool.Put(vr.r)
-	vr.r = nil
-
-	vrPool.Put(vr)
-}
-
 // NewDocumentReader returns a ValueReader using b for the underlying BSON
 // representation.
 func NewDocumentReader(r io.Reader) ValueReader {
@@ -295,28 +253,14 @@ func (vr *valueReader) appendNextElement(dst []byte) ([]byte, error) {
 		return nil, err
 	}
 
-	buf, err := vr.r.Peek(int(length))
+	buf := make([]byte, length)
+	_, err = io.ReadFull(vr.r, buf)
 	if err != nil {
-		if err == bufio.ErrBufferFull {
-			temp := make([]byte, length)
-			if _, err = io.ReadFull(vr.r, temp); err != nil {
-				return nil, err
-			}
-			dst = append(dst, temp...)
-			vr.offset += int64(len(temp))
-			return dst, nil
-		}
-
 		return nil, err
 	}
-
 	dst = append(dst, buf...)
-	if _, err = vr.r.Discard(int(length)); err != nil {
-		return nil, err
-	}
-
-	vr.offset += int64(length)
-	return dst, nil
+	vr.offset += int64(len(buf))
+	return dst, err
 }
 
 func (vr *valueReader) readValueBytes(dst []byte) (Type, []byte, error) {

bson/value_writer.go

@@ -33,29 +33,6 @@ func putValueWriter(vw *valueWriter) {
 	}
 }
 
-var documentWriterPool = sync.Pool{
-	New: func() interface{} {
-		return newDocumentWriter(nil)
-	},
-}
-
-func getDocumentWriter(w io.Writer) *valueWriter {
-	vw := documentWriterPool.Get().(*valueWriter)
-
-	vw.reset(vw.buf)
-	vw.buf = vw.buf[:0]
-	vw.w = w
-
-	return vw
-}
-
-func putDocumentWriter(vw *valueWriter) {
-	if vw != nil {
-		vw.w = nil // don't leak the writer
-		documentWriterPool.Put(vw)
-	}
-}
-
 // This is here so that during testing we can change it and not require
 // allocating a 4GB slice.
 var maxSize = math.MaxInt32