initial chain search

p2p/cuprate-p2p/src/block_downloader.rs

@@ -1,14 +1,24 @@
 //! # Block Downloader
 //!
 
+use std::collections::VecDeque;
 use std::sync::Arc;
 
 use monero_serai::{block::Block, transaction::Transaction};
+use rand::prelude::*;
+use tokio::task::JoinSet;
+use tower::{Service, ServiceExt};
 
-use async_buffer::BufferStream;
-use monero_p2p::{handles::ConnectionHandle, NetworkZone};
+use async_buffer::{BufferAppender, BufferStream};
+use monero_p2p::{
+    handles::ConnectionHandle,
+    services::{PeerSyncRequest, PeerSyncResponse},
+    NetworkZone, PeerRequest, PeerResponse, PeerSyncSvc,
+};
+use monero_wire::protocol::ChainRequest;
 
 use crate::client_pool::ClientPool;
+use crate::constants::INITIAL_CHAIN_REQUESTS_TO_SEND;
 
 /// A downloaded batch of blocks.
 pub struct BlockBatch {
@@ -28,6 +38,34 @@ pub struct BlockDownloaderConfig {
     in_progress_queue_size: usize,
 }
 
+#[derive(Debug, Copy, Clone, PartialOrd, PartialEq, Ord, Eq, thiserror::Error)]
+pub enum BlockDownloadError {
+    #[error("Failed to find a more advanced chain to follow")]
+    FailedToFindAChainToFollow,
+    #[error("Service error: {0}")]
+    ServiceError(#[from] tower::BoxError),
+}
+
+/// The request type for the chain service.
+pub enum ChainSvcRequest {
+    /// A request for the current chain history.
+    CompactHistory,
+    /// A request to find the first unknown
+    FindFirstUnknown(Vec<[u8; 32]>),
+}
+
+/// The response type for the chain service.
+pub enum ChainSvcResponse {
+    /// The response for [`ChainSvcRequest::CompactHistory`]
+    CompactHistory {
+        block_ids: Vec<[u8; 32]>,
+        cumulative_difficulty: u128,
+    },
+    /// The response for [`ChainSvcRequest::FindFirstUnknown`], contains the index of the first unknown
+    /// block.
+    FindFirstUnknown(usize),
+}
+
 /// # Block Downloader
 ///
 /// This function starts the block downloader and returns a [`BufferStream`] that will produce
@@ -43,5 +81,128 @@ pub fn download_blocks<N: NetworkZone, S>(
     peer_sync_svc: S,
     config: BlockDownloaderConfig,
 ) -> BufferStream<BlockBatch> {
+    let (buffer_appender, buffer_stream) = async_buffer::new_buffer(config.buffer_size);
+
+    tokio::spawn(block_downloader(
+        client_pool,
+        peer_sync_svc,
+        config,
+        buffer_appender,
+    ));
+
+    buffer_stream
+}
+
+async fn block_downloader<N: NetworkZone, S>(
+    client_pool: Arc<ClientPool<N>>,
+    peer_sync_svc: S,
+    config: BlockDownloaderConfig,
+    buffer_appender: BufferAppender<BlockBatch>,
+) -> Result<(), tower::BoxError> {
     todo!()
 }
+
+struct BestChainFound {
+    common_ancestor: [u8; 32],
+    next_hashes: VecDeque<[u8; 32]>,
+    from_peer: ConnectionHandle,
+}
+
+async fn initial_chain_search<N: NetworkZone, S, C>(
+    client_pool: &ClientPool<N>,
+    mut peer_sync_svc: S,
+    mut our_chain_svc: C,
+) -> Result<BestChainFound, BlockDownloadError>
+where
+    S: PeerSyncSvc<N>,
+    C: Service<ChainSvcRequest, Response = ChainSvcResponse> + Send + 'static,
+    C::Future: Send + 'static,
+{
+    let ChainSvcResponse::CompactHistory {
+        block_ids,
+        cumulative_difficulty,
+    } = our_chain_svc
+        .ready()
+        .await?
+        .call(ChainSvcRequest::CompactHistory)
+        .await?
+    else {
+        panic!("chain service sent wrong response.");
+    };
+
+    let PeerSyncResponse::PeersToSyncFrom(mut peers) = peer_sync_svc
+        .ready()
+        .await?
+        .call(PeerSyncRequest::PeersToSyncFrom {
+            block_needed: None,
+            current_cumulative_difficulty: cumulative_difficulty,
+        })
+        .await?
+    else {
+        panic!("peer sync service sent wrong response.");
+    };
+
+    peers.shuffle(&mut thread_rng());
+
+    let mut peers = client_pool.borrow_clients(&peers);
+
+    let mut futs = JoinSet::new();
+
+    let req = PeerRequest::GetChain(ChainRequest {
+        block_ids: block_ids.into(),
+        prune: false,
+    });
+
+    while futs.len() < INITIAL_CHAIN_REQUESTS_TO_SEND {
+        let Some(mut next_peer) = peers.next() else {
+            break;
+        };
+        let cloned_req = req.clone();
+        futs.spawn(async move {
+            let PeerResponse::GetChain(chain_res) =
+                next_peer.ready().await?.call(cloned_req).await?
+            else {
+                panic!("connection task returned wrong response!");
+            };
+
+            Ok((chain_res, next_peer.info.handle.clone()))
+        });
+    }
+
+    let mut res = None;
+
+    while let Some(task_res) = futs.join_next().await {
+        let Ok(task_res) = task_res.unwrap() else {
+            continue;
+        };
+
+        match &mut res {
+            Some(res) => {
+                if res.0.cumulative_difficulty() < task_res.0.cumulative_difficulty() {
+                    let _ = std::mem::replace(res, task_res);
+                }
+            }
+            None => {
+                let _ = std::mem::replace(&mut res, Some(task_res));
+            }
+        }
+    }
+
+    let Some((chain_res, peer_handle)) = res else {
+        return Err(BlockDownloadError::FailedToFindAChainToFollow);
+    };
+
+    let hashes: Vec<[u8; 32]> = chain_res.m_block_ids.into();
+
+    let ChainSvcResponse::FindFirstUnknown(first_unknown) = our_chain_svc
+        .ready()
+        .await?
+        .call(ChainSvcRequest::FindFirstUnknown(hashes.clone()))
+        .await?
+    else {
+        panic!("chain service sent wrong response.");
+    };
+    
+    todo!()
+    
+}

p2p/cuprate-p2p/src/constants.rs

@@ -34,6 +34,9 @@ pub(crate) const MAX_TXS_IN_BROADCAST_CHANNEL: usize = 50;
 /// TODO: it might be a good idea to make this configurable.
 pub(crate) const INBOUND_CONNECTION_COOL_DOWN: Duration = Duration::from_millis(500);
 
+/// The initial amount of chain requests to send to find the best chain to sync from.
+pub(crate) const INITIAL_CHAIN_REQUESTS_TO_SEND: usize = 3;
+
 #[cfg(test)]
 mod tests {
     use super::*;