/// <summary>
/// Processes "headers" message received from the peer.
/// </summary>
/// <param name="peer">Peer from which the message was received.</param>
/// <param name="headersPayload">Payload of "headers" message to process.</param>
/// <remarks>
/// "headers" message is sent in response to "getheaders" message or it is solicited
/// by the peer when a new block is validated (unless in IBD).
/// <para>
/// When we receive "headers" message from the peer, we can adjust our knowledge
/// of the peer's view of the chain. We update its pending tip, which represents
/// the tip of the best chain we think the peer has.
/// </para>
/// <para>
/// If we receive a valid header from peer which work is higher than the work
/// of our best chain's tip, we update our view of the best chain to that tip.
/// </para>
/// </remarks>
private async Task ProcessHeadersAsync(INetworkPeer peer, HeadersPayload headersPayload)
{
this.logger.LogTrace("({0}:'{1}',{2}:'{3}')", nameof(peer), peer.RemoteSocketEndpoint, nameof(headersPayload), headersPayload);
if (!this.CanSync)
{
this.logger.LogTrace("(-)[CANT_SYNC]");
return;
}
if (headersPayload.Headers.Count == 0)
{
this.logger.LogTrace("Headers payload with no headers was received. Assuming we're synced with the peer.");
this.logger.LogTrace("(-)[NO_HEADERS]");
return;
}
ChainedHeader pendingTipBefore = this.pendingTip;
this.logger.LogTrace("Pending tip is '{0}', received {1} new headers.", pendingTipBefore, headersPayload.Headers.Count);
bool doTrySync = false;
// TODO: implement MAX_HEADERS_RESULTS in NBitcoin.HeadersPayload
ChainedHeader tip = pendingTipBefore;
foreach (BlockHeader header in headersPayload.Headers)
{
ChainedHeader prev = tip?.FindAncestorOrSelf(header.HashPrevBlock);
if (prev == null)
{
this.logger.LogTrace("Previous header of the new header '{0}' was not found on the peer's chain, the view of the peer's chain is probably outdated.", header);
// We have received a header from the peer for which we don't register a previous header.
// This can happen if our information about where the peer is is invalid.
// However, if the previous header is on the chain that we recognize,
// we can fix it.
// Try to find the header's previous hash on our best chain.
prev = this.Chain.GetBlock(header.HashPrevBlock);
if (prev == null)
{
this.logger.LogTrace("Previous header of the new header '{0}' was not found on our chain either.", header);
// If we can't connect the header we received from the peer, we might be on completely different chain or
// a reorg happened recently. If we ignored it, we would have invalid view of the peer and the propagation
// of blocks would not work well. So we ask the peer for headers using "getheaders" message.
// Enforce a sync.
doTrySync = true;
break;
}
// Now we know the previous block header and thus we can connect the new header.
}
tip = new ChainedHeader(header, header.GetHash(), prev);
bool validated = this.Chain.GetBlock(tip.HashBlock) != null || tip.Validate(peer.Network);
validated &= !this.chainState.IsMarkedInvalid(tip.HashBlock);
if (!validated)
{
this.logger.LogTrace("Validation of new header '{0}' failed.", tip);
this.InvalidHeaderReceived = true;
break;
}
this.pendingTip = tip;
}
if (pendingTipBefore != this.pendingTip)
{
this.logger.LogTrace("Pending tip changed to '{0}'.", this.pendingTip);
}
if ((this.pendingTip != null) && !this.bestChainSelector.TrySetAvailableTip(this.AttachedPeer.Connection.Id, this.pendingTip))
{
this.InvalidHeaderReceived = true;
}
ChainedHeader chainedPendingTip = this.pendingTip == null ? null : this.Chain.GetBlock(this.pendingTip.HashBlock);
if (chainedPendingTip != null)
{
// This allows garbage collection to collect the duplicated pendingTip and ancestors.
this.pendingTip = chainedPendingTip;
}
// If we made any advancement or the sync is enforced by 'doTrySync'- continue syncing.
if (doTrySync || (this.pendingTip == null) || (pendingTipBefore == null) || (pendingTipBefore.HashBlock != this.pendingTip.HashBlock))
{
await this.TrySyncAsync().ConfigureAwait(false);
}
this.logger.LogTrace("(-)");
}
