lbcd/wire/msggetheaders.go

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// Copyright (c) 2013-2015 The btcsuite developers
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// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.
package wire
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import (
"fmt"
"io"
)
// 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 []*ShaHash
HashStop ShaHash
}
// AddBlockLocatorHash adds a new block locator hash to the message.
func (msg *MsgGetHeaders) AddBlockLocatorHash(hash *ShaHash) 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)
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}
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)
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}
msg.BlockLocatorHashes = make([]*ShaHash, 0, count)
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for i := uint64(0); i < count; i++ {
sha := ShaHash{}
err := readElement(r, &sha)
if err != nil {
return err
}
msg.AddBlockLocatorHash(&sha)
}
err = readElement(r, &msg.HashStop)
if err != nil {
return err
}
return nil
}
// 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)
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}
err := writeElement(w, msg.ProtocolVersion)
if err != nil {
return err
}
err = writeVarInt(w, pver, uint64(count))
if err != nil {
return err
}
for _, sha := range msg.BlockLocatorHashes {
err := writeElement(w, sha)
if err != nil {
return err
}
}
err = writeElement(w, &msg.HashStop)
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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 *MsgGetHeaders) Command() string {
return CmdGetHeaders
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}
// 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.
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return 4 + MaxVarIntPayload + (MaxBlockLocatorsPerMsg * HashSize) + HashSize
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}
// NewMsgGetHeaders returns a new bitcoin getheaders message that conforms to
// the Message interface. See MsgGetHeaders for details.
func NewMsgGetHeaders() *MsgGetHeaders {
return &MsgGetHeaders{
BlockLocatorHashes: make([]*ShaHash, 0, MaxBlockLocatorsPerMsg),
}
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}