[CLIENT-2624] BatchGetOperate triggering SIGSEGV nil pointer in go cl…

…ient

Caching of the operation is faulty and causes race conditions when used concurrently.
This commit removes the caching which included a usesless allocation and
rarely, if ever, had any practical influence on performance.

command.go

@@ -2260,13 +2260,6 @@ func (cmd *baseCommand) writeBatchReadOperations(ops []*Operation, readAttr int)
 func (cmd *baseCommand) writeOperationForOperation(operation *Operation) Error {
 	nameLength := copy(cmd.dataBuffer[(cmd.dataOffset+int(_OPERATION_HEADER_SIZE)):], operation.binName)
 
-	if operation.used {
-		// cahce will set the used flag to false again
-		if err := operation.cache(); err != nil {
-			return err
-		}
-	}
-
 	if operation.encoder == nil {
 		valueLength, err := operation.binValue.EstimateSize()
 		if err != nil {
@@ -2295,8 +2288,6 @@ func (cmd *baseCommand) writeOperationForOperation(operation *Operation) Error {
 	cmd.WriteByte((byte(nameLength)))
 	cmd.dataOffset += nameLength
 	_, err = operation.encoder(operation, cmd)
-	//mark the operation as used, so that it will be cached the next time it is used
-	operation.used = err == nil
 	return err
 }
 

operation.go

@@ -115,23 +115,12 @@ type Operation struct {
 
 	// will be true ONLY for GetHeader() operation
 	headerOnly bool
-
-	// reused determines if the operation is cached. If so, it will cache the
-	// internal bytes in binValue field and remove the encoder for maximum performance
-	used bool
 }
 
 // size returns the size of the operation on the wire protocol.
 func (op *Operation) size() (int, Error) {
 	size := len(op.binName)
 
-	if op.used {
-		// cahce will set the used flag to false again
-		if err := op.cache(); err != nil {
-			return -1, err
-		}
-	}
-
 	// Simple case
 	if op.encoder == nil {
 		valueLength, err := op.binValue.EstimateSize()
@@ -162,20 +151,6 @@ func (op *Operation) grpc() *kvs.Operation {
 	}
 }
 
-// cache uses the encoder and caches the packed operation for further use.
-func (op *Operation) cache() Error {
-	packer := newPacker()
-
-	if _, err := op.encoder(op, packer); err != nil {
-		return err
-	}
-
-	op.binValue = BytesValue(packer.Bytes())
-	op.encoder = nil // do not encode anymore; just use the cache
-	op.used = false  // do not encode anymore; just use the cache
-	return nil
-}
-
 // GetBinOp creates read bin database operation.
 func GetBinOp(binName string) *Operation {
 	return &Operation{opType: _READ, binName: binName, binValue: NewNullValue()}