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msggetheaders.go
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/
msggetheaders.go
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package wire
import (
"fmt"
"io"
chainhash "github.com/l0k18/pod/pkg/chain/hash"
)
// 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, enc MessageEncoding) error {
err := readElement(r, &msg.ProtocolVersion)
if err != nil {
Error(err)
return err
}
// Read num block locator hashes and limit to max.
count, err := ReadVarInt(r, pver)
if err != nil {
Error(err)
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 {
Error(err)
return err
}
err = msg.AddBlockLocatorHash(hash)
if err != nil {
Error(err)
}
}
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, enc MessageEncoding) 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 {
Error(err)
return err
}
err = WriteVarInt(w, pver, uint64(count))
if err != nil {
Error(err)
return err
}
for _, hash := range msg.BlockLocatorHashes {
err := writeElement(w, hash)
if err != nil {
Error(err)
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),
}
}