136 lines
4.5 KiB
Go
136 lines
4.5 KiB
Go
// Copyright (c) 2013-2016 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"
|
|
|
|
"github.com/btcsuite/btcd/chaincfg/chainhash"
|
|
)
|
|
|
|
// MsgGetHeaders implements the Message interface and represents a bitcoin
|
|
// getheaders message. It is used to request a list of block headers for
|
|
// blocks starting after the last known hash in the slice of block locator
|
|
// hashes. The list is returned via a headers message (MsgHeaders) and is
|
|
// limited by a specific hash to stop at or the maximum number of block headers
|
|
// per message, which is currently 2000.
|
|
//
|
|
// Set the HashStop field to the hash at which to stop and use
|
|
// AddBlockLocatorHash to build up the list of block locator hashes.
|
|
//
|
|
// The algorithm for building the block locator hashes should be to add the
|
|
// hashes in reverse order until you reach the genesis block. In order to keep
|
|
// the list of locator hashes to a resonable number of entries, first add the
|
|
// most recent 10 block hashes, then double the step each loop iteration to
|
|
// exponentially decrease the number of hashes the further away from head and
|
|
// closer to the genesis block you get.
|
|
type MsgGetHeaders struct {
|
|
ProtocolVersion uint32
|
|
BlockLocatorHashes []*chainhash.Hash
|
|
HashStop chainhash.Hash
|
|
}
|
|
|
|
// AddBlockLocatorHash adds a new block locator hash to the message.
|
|
func (msg *MsgGetHeaders) AddBlockLocatorHash(hash *chainhash.Hash) error {
|
|
if len(msg.BlockLocatorHashes)+1 > MaxBlockLocatorsPerMsg {
|
|
str := fmt.Sprintf("too many block locator hashes for message [max %v]",
|
|
MaxBlockLocatorsPerMsg)
|
|
return messageError("MsgGetHeaders.AddBlockLocatorHash", str)
|
|
}
|
|
|
|
msg.BlockLocatorHashes = append(msg.BlockLocatorHashes, hash)
|
|
return nil
|
|
}
|
|
|
|
// BtcDecode decodes r using the bitcoin protocol encoding into the receiver.
|
|
// This is part of the Message interface implementation.
|
|
func (msg *MsgGetHeaders) BtcDecode(r io.Reader, pver uint32) error {
|
|
err := readElement(r, &msg.ProtocolVersion)
|
|
if err != nil {
|
|
return err
|
|
}
|
|
|
|
// Read num block locator hashes and limit to max.
|
|
count, err := ReadVarInt(r, pver)
|
|
if err != nil {
|
|
return err
|
|
}
|
|
if count > MaxBlockLocatorsPerMsg {
|
|
str := fmt.Sprintf("too many block locator hashes for message "+
|
|
"[count %v, max %v]", count, MaxBlockLocatorsPerMsg)
|
|
return messageError("MsgGetHeaders.BtcDecode", str)
|
|
}
|
|
|
|
// Create a contiguous slice of hashes to deserialize into in order to
|
|
// reduce the number of allocations.
|
|
locatorHashes := make([]chainhash.Hash, count)
|
|
msg.BlockLocatorHashes = make([]*chainhash.Hash, 0, count)
|
|
for i := uint64(0); i < count; i++ {
|
|
hash := &locatorHashes[i]
|
|
err := readElement(r, hash)
|
|
if err != nil {
|
|
return err
|
|
}
|
|
msg.AddBlockLocatorHash(hash)
|
|
}
|
|
|
|
return readElement(r, &msg.HashStop)
|
|
}
|
|
|
|
// BtcEncode encodes the receiver to w using the bitcoin protocol encoding.
|
|
// This is part of the Message interface implementation.
|
|
func (msg *MsgGetHeaders) BtcEncode(w io.Writer, pver uint32) error {
|
|
// Limit to max block locator hashes per message.
|
|
count := len(msg.BlockLocatorHashes)
|
|
if count > MaxBlockLocatorsPerMsg {
|
|
str := fmt.Sprintf("too many block locator hashes for message "+
|
|
"[count %v, max %v]", count, MaxBlockLocatorsPerMsg)
|
|
return messageError("MsgGetHeaders.BtcEncode", str)
|
|
}
|
|
|
|
err := writeElement(w, msg.ProtocolVersion)
|
|
if err != nil {
|
|
return err
|
|
}
|
|
|
|
err = WriteVarInt(w, pver, uint64(count))
|
|
if err != nil {
|
|
return err
|
|
}
|
|
|
|
for _, hash := range msg.BlockLocatorHashes {
|
|
err := writeElement(w, hash)
|
|
if err != nil {
|
|
return err
|
|
}
|
|
}
|
|
|
|
return writeElement(w, &msg.HashStop)
|
|
}
|
|
|
|
// Command returns the protocol command string for the message. This is part
|
|
// of the Message interface implementation.
|
|
func (msg *MsgGetHeaders) Command() string {
|
|
return CmdGetHeaders
|
|
}
|
|
|
|
// MaxPayloadLength returns the maximum length the payload can be for the
|
|
// receiver. This is part of the Message interface implementation.
|
|
func (msg *MsgGetHeaders) MaxPayloadLength(pver uint32) uint32 {
|
|
// Version 4 bytes + num block locator hashes (varInt) + max allowed block
|
|
// locators + hash stop.
|
|
return 4 + MaxVarIntPayload + (MaxBlockLocatorsPerMsg *
|
|
chainhash.HashSize) + chainhash.HashSize
|
|
}
|
|
|
|
// NewMsgGetHeaders returns a new bitcoin getheaders message that conforms to
|
|
// the Message interface. See MsgGetHeaders for details.
|
|
func NewMsgGetHeaders() *MsgGetHeaders {
|
|
return &MsgGetHeaders{
|
|
BlockLocatorHashes: make([]*chainhash.Hash, 0,
|
|
MaxBlockLocatorsPerMsg),
|
|
}
|
|
}
|