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msggetdata.go
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msggetdata.go
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// Copyright (c) 2013-2015 The btcsuite developers
// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.
package wire
import (
"fmt"
"io"
)
// MsgGetData implements the Message interface and represents a litecoin
// getdata message. It is used to request data such as blocks and transactions
// from another peer. It should be used in response to the inv (MsgInv) message
// to request the actual data referenced by each inventory vector the receiving
// peer doesn't already have. Each message is limited to a maximum number of
// inventory vectors, which is currently 50,000. As a result, multiple messages
// must be used to request larger amounts of data.
//
// Use the AddInvVect function to build up the list of inventory vectors when
// sending a getdata message to another peer.
type MsgGetData struct {
InvList []*InvVect
}
// AddInvVect adds an inventory vector to the message.
func (msg *MsgGetData) AddInvVect(iv *InvVect) error {
if len(msg.InvList)+1 > MaxInvPerMsg {
str := fmt.Sprintf("too many invvect in message [max %v]",
MaxInvPerMsg)
return messageError("MsgGetData.AddInvVect", str)
}
msg.InvList = append(msg.InvList, iv)
return nil
}
// BtcDecode decodes r using the litecoin protocol encoding into the receiver.
// This is part of the Message interface implementation.
func (msg *MsgGetData) BtcDecode(r io.Reader, pver uint32, enc MessageEncoding) error {
count, err := ReadVarInt(r, pver)
if err != nil {
return err
}
// Limit to max inventory vectors per message.
if count > MaxInvPerMsg {
str := fmt.Sprintf("too many invvect in message [%v]", count)
return messageError("MsgGetData.BtcDecode", str)
}
// Create a contiguous slice of inventory vectors to deserialize into in
// order to reduce the number of allocations.
invList := make([]InvVect, count)
msg.InvList = make([]*InvVect, 0, count)
for i := uint64(0); i < count; i++ {
iv := &invList[i]
err := readInvVect(r, pver, iv)
if err != nil {
return err
}
msg.AddInvVect(iv)
}
return nil
}
// BtcEncode encodes the receiver to w using the litecoin protocol encoding.
// This is part of the Message interface implementation.
func (msg *MsgGetData) BtcEncode(w io.Writer, pver uint32, enc MessageEncoding) error {
// Limit to max inventory vectors per message.
count := len(msg.InvList)
if count > MaxInvPerMsg {
str := fmt.Sprintf("too many invvect in message [%v]", count)
return messageError("MsgGetData.BtcEncode", str)
}
err := WriteVarInt(w, pver, uint64(count))
if err != nil {
return err
}
for _, iv := range msg.InvList {
err := writeInvVect(w, pver, iv)
if err != nil {
return err
}
}
return nil
}
// Command returns the protocol command string for the message. This is part
// of the Message interface implementation.
func (msg *MsgGetData) Command() string {
return CmdGetData
}
// MaxPayloadLength returns the maximum length the payload can be for the
// receiver. This is part of the Message interface implementation.
func (msg *MsgGetData) MaxPayloadLength(pver uint32) uint32 {
// Num inventory vectors (varInt) + max allowed inventory vectors.
return MaxVarIntPayload + (MaxInvPerMsg * maxInvVectPayload)
}
// NewMsgGetData returns a new litecoin getdata message that conforms to the
// Message interface. See MsgGetData for details.
func NewMsgGetData() *MsgGetData {
return &MsgGetData{
InvList: make([]*InvVect, 0, defaultInvListAlloc),
}
}
// NewMsgGetDataSizeHint returns a new litecoin getdata message that conforms to
// the Message interface. See MsgGetData for details. This function differs
// from NewMsgGetData in that it allows a default allocation size for the
// backing array which houses the inventory vector list. This allows callers
// who know in advance how large the inventory list will grow to avoid the
// overhead of growing the internal backing array several times when appending
// large amounts of inventory vectors with AddInvVect. Note that the specified
// hint is just that - a hint that is used for the default allocation size.
// Adding more (or less) inventory vectors will still work properly. The size
// hint is limited to MaxInvPerMsg.
func NewMsgGetDataSizeHint(sizeHint uint) *MsgGetData {
// Limit the specified hint to the maximum allow per message.
if sizeHint > MaxInvPerMsg {
sizeHint = MaxInvPerMsg
}
return &MsgGetData{
InvList: make([]*InvVect, 0, sizeHint),
}
}