lbcd/msgblock.go

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// Copyright (c) 2013 Conformal Systems LLC.
// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.
package btcwire
import (
"bytes"
"fmt"
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"io"
)
// defaultTransactionAlloc is the default size used for the backing array
// for transactions. The transaction array will dynamically grow as needed, but
// this figure is intended to provide enough space for the number of
// transactions in the vast majority of blocks without needing to grow the
// backing array multiple times.
const defaultTransactionAlloc = 2048
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// MaxBlocksPerMsg is the maximum number of blocks allowed per message.
const MaxBlocksPerMsg = 500
// MaxBlockPayload is the maximum bytes a block message can be in bytes.
const MaxBlockPayload = 1000000 // Not actually 1MB which would be 1024 * 1024
// maxTxPerBlock is the maximum number of transactions that could
// possibly fit into a block.
const maxTxPerBlock = (MaxBlockPayload / minTxPayload) + 1
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// TxLoc holds locator data for the offset and length of where a transaction is
// located within a MsgBlock data buffer.
type TxLoc struct {
TxStart int
TxLen int
}
// MsgBlock implements the Message interface and represents a bitcoin
// block message. It is used to deliver block and transaction information in
// response to a getdata message (MsgGetData) for a given block hash.
//
// NOTE: Unlike the other message types which contain slices, the number of
// transactions has a specific entry (Header.TxnCount) that must be kept in
// sync. The AddTransaction and ClearTransactions functions properly sync the
// value, but if you are manually modifying the public members, you will need
// to ensure you update the Header.TxnCount when you add and remove
// transactions.
type MsgBlock struct {
Header BlockHeader
Transactions []*MsgTx
}
// AddTransaction adds a transaction to the message and updates Header.TxnCount
// accordingly.
func (msg *MsgBlock) AddTransaction(tx *MsgTx) error {
// TODO: Return error if adding the transaction would make the message
// too large.
msg.Transactions = append(msg.Transactions, tx)
msg.Header.TxnCount = uint64(len(msg.Transactions))
return nil
}
// ClearTransactions removes all transactions from the message and updates
// Header.TxnCount accordingly.
func (msg *MsgBlock) ClearTransactions() {
msg.Transactions = make([]*MsgTx, 0, defaultTransactionAlloc)
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msg.Header.TxnCount = 0
}
// BtcDecode decodes r using the bitcoin protocol encoding into the receiver.
// This is part of the Message interface implementation.
// See Deserialize for decoding blocks stored to disk, such as in a database, as
// opposed to decoding blocks from the wire.
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func (msg *MsgBlock) BtcDecode(r io.Reader, pver uint32) error {
err := readBlockHeader(r, pver, &msg.Header)
if err != nil {
return err
}
// Prevent more transactions than could possibly fit into a block.
// It would be possible to cause memory exhaustion and panics without
// a sane upper bound on this count.
txCount := msg.Header.TxnCount
if txCount > maxTxPerBlock {
str := fmt.Sprintf("too many transactions to fit into a block "+
"[count %d, max %d]", txCount, maxTxPerBlock)
return messageError("MsgBlock.BtcDecode", str)
}
msg.Transactions = make([]*MsgTx, 0, txCount)
for i := uint64(0); i < txCount; i++ {
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tx := MsgTx{}
err := tx.BtcDecode(r, pver)
if err != nil {
return err
}
msg.Transactions = append(msg.Transactions, &tx)
}
return nil
}
// Deserialize decodes a block from r into the receiver using a format that is
// suitable for long-term storage such as a database while respecting the
// Version field in the block. This function differs from BtcDecode in that
// BtcDecode decodes from the bitcoin wire protocol as it was sent across the
// network. The wire encoding can technically differ depending on the protocol
// version and doesn't even really need to match the format of a stored block at
// all. As of the time this comment was written, the encoded block is the same
// in both instances, but there is a distinct difference and separating the two
// allows the API to be flexible enough to deal with changes.
func (msg *MsgBlock) Deserialize(r io.Reader) error {
// At the current time, there is no difference between the wire encoding
// at protocol version 0 and the stable long-term storage format. As
// a result, make use of BtcDecode.
return msg.BtcDecode(r, 0)
}
// DeserializeTxLoc decodes r in the same manner Deserialize does, but it takes
// a byte buffer instead of a generic reader and returns a slice containing the start and length of
// each transaction within the raw data that is being deserialized.
func (msg *MsgBlock) DeserializeTxLoc(r *bytes.Buffer) ([]TxLoc, error) {
fullLen := r.Len()
// At the current time, there is no difference between the wire encoding
// at protocol version 0 and the stable long-term storage format. As
// a result, make use of existing wire protocol functions.
err := readBlockHeader(r, 0, &msg.Header)
if err != nil {
return nil, err
}
// Prevent more transactions than could possibly fit into a block.
// It would be possible to cause memory exhaustion and panics without
// a sane upper bound on this count.
txCount := msg.Header.TxnCount
if txCount > maxTxPerBlock {
str := fmt.Sprintf("too many transactions to fit into a block "+
"[count %d, max %d]", txCount, maxTxPerBlock)
return nil, messageError("MsgBlock.DeserializeTxLoc", str)
}
// Deserialize each transaction while keeping track of its location
// within the byte stream.
msg.Transactions = make([]*MsgTx, 0, txCount)
txLocs := make([]TxLoc, txCount)
for i := uint64(0); i < txCount; i++ {
txLocs[i].TxStart = fullLen - r.Len()
tx := MsgTx{}
err := tx.Deserialize(r)
if err != nil {
return nil, err
}
msg.Transactions = append(msg.Transactions, &tx)
txLocs[i].TxLen = (fullLen - r.Len()) - txLocs[i].TxStart
}
return txLocs, nil
}
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// BtcEncode encodes the receiver to w using the bitcoin protocol encoding.
// This is part of the Message interface implementation.
// See Serialize for encoding blocks to be stored to disk, such as in a
// database, as opposed to encoding blocks for the wire.
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func (msg *MsgBlock) BtcEncode(w io.Writer, pver uint32) error {
msg.Header.TxnCount = uint64(len(msg.Transactions))
err := writeBlockHeader(w, pver, &msg.Header)
if err != nil {
return err
}
for _, tx := range msg.Transactions {
err = tx.BtcEncode(w, pver)
if err != nil {
return err
}
}
return nil
}
// Serialize encodes the block to w using a format that suitable for long-term
// storage such as a database while respecting the Version field in the block.
// This function differs from BtcEncode in that BtcEncode encodes the block to
// the bitcoin wire protocol in order to be sent across the network. The wire
// encoding can technically differ depending on the protocol version and doesn't
// even really need to match the format of a stored block at all. As of the
// time this comment was written, the encoded block is the same in both
// instances, but there is a distinct difference and separating the two allows
// the API to be flexible enough to deal with changes.
func (msg *MsgBlock) Serialize(w io.Writer) error {
// At the current time, there is no difference between the wire encoding
// at protocol version 0 and the stable long-term storage format. As
// a result, make use of BtcEncode.
return msg.BtcEncode(w, 0)
}
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// Command returns the protocol command string for the message. This is part
// of the Message interface implementation.
func (msg *MsgBlock) Command() string {
return cmdBlock
}
// MaxPayloadLength returns the maximum length the payload can be for the
// receiver. This is part of the Message interface implementation.
func (msg *MsgBlock) MaxPayloadLength(pver uint32) uint32 {
// Block header at 81 bytes + max transactions which can vary up to the
// maxBlockPayload (including the block header).
return MaxBlockPayload
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}
// BlockSha computes the block identifier hash for this block.
func (msg *MsgBlock) BlockSha() (ShaHash, error) {
return msg.Header.BlockSha()
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}
// TxShas returns a slice of hashes of all of transactions in this block.
func (msg *MsgBlock) TxShas() ([]ShaHash, error) {
shaList := make([]ShaHash, 0, len(msg.Transactions))
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for _, tx := range msg.Transactions {
// Ignore error here since TxSha can't fail in the current
// implementation except due to run-time panics.
sha, _ := tx.TxSha()
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shaList = append(shaList, sha)
}
return shaList, nil
}
// NewMsgBlock returns a new bitcoin block message that conforms to the
// Message interface. See MsgBlock for details.
func NewMsgBlock(blockHeader *BlockHeader) *MsgBlock {
return &MsgBlock{
Header: *blockHeader,
Transactions: make([]*MsgTx, 0, defaultTransactionAlloc),
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}
}