// PushGetBlocksMsg sends a getblocks message for the provided block locator
// and stop hash. It will ignore back-to-back duplicate requests.
func (p *peer) PushGetBlocksMsg(locator btcchain.BlockLocator, stopHash *btcwire.ShaHash) error {
// Extract the begin hash from the block locator, if one was specified,
// to use for filtering duplicate getblocks requests.
// request.
var beginHash *btcwire.ShaHash
if len(locator) > 0 {
beginHash = locator[0]
}
// Filter duplicate getblocks requests.
if p.prevGetBlocksStop != nil && p.prevGetBlocksBegin != nil &&
beginHash != nil && stopHash.IsEqual(p.prevGetBlocksStop) &&
beginHash.IsEqual(p.prevGetBlocksBegin) {
log.Tracef("PEER: Filtering duplicate [getblocks] with begin "+
"hash %v, stop hash %v", beginHash, stopHash)
return nil
}
// Construct the getblocks request and queue it to be sent.
msg := btcwire.NewMsgGetBlocks(stopHash)
for _, hash := range locator {
err := msg.AddBlockLocatorHash(hash)
if err != nil {
return err
}
}
p.QueueMessage(msg, nil)
// Update the previous getblocks request information for filtering
// duplicates.
p.prevGetBlocksBegin = beginHash
p.prevGetBlocksStop = stopHash
return nil
}
// BlockLocatorFromHash returns a block locator for the passed block hash.
// See BlockLocator for details on the algotirhm used to create a block locator.
//
// In addition to the general algorithm referenced above, there are a couple of
// special cases which are handled:
//
// - If the genesis hash is passed, there are no previous hashes to add and
// therefore the block locator will only consist of the genesis hash
// - If the passed hash is not currently known, the block locator will only
// consist of the passed hash
func (b *BlockChain) BlockLocatorFromHash(hash *btcwire.ShaHash) BlockLocator {
// The locator contains the requested hash at the very least.
locator := make(BlockLocator, 0, btcwire.MaxBlockLocatorsPerMsg)
locator = append(locator, hash)
// Nothing more to do if a locator for the genesis hash was requested.
if hash.IsEqual(b.chainParams().GenesisHash) {
return locator
}
// Attempt to find the height of the block that corresponds to the
// passed hash, and if it's on a side chain, also find the height at
// which it forks from the main chain.
blockHeight := int64(-1)
forkHeight := int64(-1)
node, exists := b.index[*hash]
if !exists {
// Try to look up the height for passed block hash. Assume an
// error means it doesn't exist and just return the locator for
// the block itself.
block, err := b.db.FetchBlockBySha(hash)
if err != nil {
return locator
}
blockHeight = block.Height()
} else {
blockHeight = node.height
// Find the height at which this node forks from the main chain
// if the node is on a side chain.
if !node.inMainChain {
for n := node; n.parent != nil; n = n.parent {
if n.inMainChain {
forkHeight = n.height
break
}
}
}
}
// Generate the block locators according to the algorithm described in
// in the BlockLocator comment and make sure to leave room for the
// final genesis hash.
iterNode := node
increment := int64(1)
for len(locator) < btcwire.MaxBlockLocatorsPerMsg-1 {
// Once there are 10 locators, exponentially increase the
// distance between each block locator.
if len(locator) > 10 {
increment *= 2
}
blockHeight -= increment
if blockHeight < 1 {
break
}
// As long as this is still on the side chain, walk backwards
// along the side chain nodes to each block height.
if forkHeight != -1 && blockHeight > forkHeight {
// Intentionally use parent field instead of the
// getPrevNodeFromNode function since we don't want to
// dynamically load nodes when building block locators.
// Side chain blocks should always be in memory already,
// and if they aren't for some reason it's ok to skip
// them.
for iterNode != nil && blockHeight > iterNode.height {
iterNode = iterNode.parent
}
if iterNode != nil && iterNode.height == blockHeight {
locator = append(locator, iterNode.hash)
}
continue
}
// The desired block height is in the main chain, so look it up
// from the main chain database.
h, err := b.db.FetchBlockShaByHeight(blockHeight)
if err != nil {
// This shouldn't happen and it's ok to ignore block
// locators, so just continue to the next one.
log.Warnf("Lookup of known valid height failed %v",
blockHeight)
continue
}
locator = append(locator, h)
}
// Append the appropriate genesis block.
locator = append(locator, b.chainParams().GenesisHash)
return locator
}