140 lines
4.6 KiB
Go
140 lines
4.6 KiB
Go
// Copyright (c) 2013-2016 The btcsuite developers
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// Use of this source code is governed by an ISC
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// license that can be found in the LICENSE file.
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package wire
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import (
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"fmt"
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"io"
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"github.com/btcsuite/btcd/chaincfg/chainhash"
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)
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// MaxBlockLocatorsPerMsg is the maximum number of block locator hashes allowed
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// per message.
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const MaxBlockLocatorsPerMsg = 500
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// MsgGetBlocks implements the Message interface and represents a bitcoin
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// getblocks message. It is used to request a list of blocks starting after the
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// last known hash in the slice of block locator hashes. The list is returned
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// via an inv message (MsgInv) and is limited by a specific hash to stop at or
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// the maximum number of blocks per message, which is currently 500.
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//
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// Set the HashStop field to the hash at which to stop and use
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// AddBlockLocatorHash to build up the list of block locator hashes.
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//
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// The algorithm for building the block locator hashes should be to add the
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// hashes in reverse order until you reach the genesis block. In order to keep
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// the list of locator hashes to a reasonable number of entries, first add the
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// most recent 10 block hashes, then double the step each loop iteration to
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// exponentially decrease the number of hashes the further away from head and
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// closer to the genesis block you get.
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type MsgGetBlocks struct {
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ProtocolVersion uint32
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BlockLocatorHashes []*chainhash.Hash
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HashStop chainhash.Hash
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}
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// AddBlockLocatorHash adds a new block locator hash to the message.
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func (msg *MsgGetBlocks) AddBlockLocatorHash(hash *chainhash.Hash) error {
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if len(msg.BlockLocatorHashes)+1 > MaxBlockLocatorsPerMsg {
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str := fmt.Sprintf("too many block locator hashes for message [max %v]",
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MaxBlockLocatorsPerMsg)
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return messageError("MsgGetBlocks.AddBlockLocatorHash", str)
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}
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msg.BlockLocatorHashes = append(msg.BlockLocatorHashes, hash)
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return nil
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}
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// BtcDecode decodes r using the bitcoin protocol encoding into the receiver.
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// This is part of the Message interface implementation.
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func (msg *MsgGetBlocks) BtcDecode(r io.Reader, pver uint32) error {
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err := readElement(r, &msg.ProtocolVersion)
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if err != nil {
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return err
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}
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// Read num block locator hashes and limit to max.
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count, err := ReadVarInt(r, pver)
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if err != nil {
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return err
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}
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if count > MaxBlockLocatorsPerMsg {
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str := fmt.Sprintf("too many block locator hashes for message "+
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"[count %v, max %v]", count, MaxBlockLocatorsPerMsg)
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return messageError("MsgGetBlocks.BtcDecode", str)
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}
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// Create a contiguous slice of hashes to deserialize into in order to
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// reduce the number of allocations.
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locatorHashes := make([]chainhash.Hash, count)
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msg.BlockLocatorHashes = make([]*chainhash.Hash, 0, count)
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for i := uint64(0); i < count; i++ {
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hash := &locatorHashes[i]
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err := readElement(r, hash)
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if err != nil {
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return err
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}
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msg.AddBlockLocatorHash(hash)
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}
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return readElement(r, &msg.HashStop)
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}
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// BtcEncode encodes the receiver to w using the bitcoin protocol encoding.
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// This is part of the Message interface implementation.
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func (msg *MsgGetBlocks) BtcEncode(w io.Writer, pver uint32) error {
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count := len(msg.BlockLocatorHashes)
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if count > MaxBlockLocatorsPerMsg {
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str := fmt.Sprintf("too many block locator hashes for message "+
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"[count %v, max %v]", count, MaxBlockLocatorsPerMsg)
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return messageError("MsgGetBlocks.BtcEncode", str)
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}
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err := writeElement(w, msg.ProtocolVersion)
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if err != nil {
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return err
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}
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err = WriteVarInt(w, pver, uint64(count))
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if err != nil {
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return err
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}
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for _, hash := range msg.BlockLocatorHashes {
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err = writeElement(w, hash)
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if err != nil {
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return err
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}
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}
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return writeElement(w, &msg.HashStop)
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}
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// Command returns the protocol command string for the message. This is part
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// of the Message interface implementation.
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func (msg *MsgGetBlocks) Command() string {
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return CmdGetBlocks
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}
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// MaxPayloadLength returns the maximum length the payload can be for the
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// receiver. This is part of the Message interface implementation.
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func (msg *MsgGetBlocks) MaxPayloadLength(pver uint32) uint32 {
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// Protocol version 4 bytes + num hashes (varInt) + max block locator
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// hashes + hash stop.
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return 4 + MaxVarIntPayload + (MaxBlockLocatorsPerMsg * chainhash.HashSize) + chainhash.HashSize
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}
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// NewMsgGetBlocks returns a new bitcoin getblocks message that conforms to the
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// Message interface using the passed parameters and defaults for the remaining
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// fields.
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func NewMsgGetBlocks(hashStop *chainhash.Hash) *MsgGetBlocks {
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return &MsgGetBlocks{
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ProtocolVersion: ProtocolVersion,
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BlockLocatorHashes: make([]*chainhash.Hash, 0, MaxBlockLocatorsPerMsg),
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HashStop: *hashStop,
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}
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}
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