Refactor snap-sync. (#2916)

* Refactor snap-sync.

- add optional target block
- add conditional block import

* Update crates/subspace-service/src/sync_from_dsn/snap_sync.rs

Co-authored-by: Nazar Mokrynskyi <[email protected]>

* Change condition for target_block (snap-sync).

* Refactor snap-sync.

* Remove import_state_block_only variable

---------

Co-authored-by: Nazar Mokrynskyi <[email protected]>

crates/subspace-service/src/sync_from_dsn/snap_sync.rs

@@ -22,7 +22,7 @@ use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::Arc;
 use std::time::Duration;
 use subspace_archiving::reconstructor::Reconstructor;
-use subspace_core_primitives::SegmentIndex;
+use subspace_core_primitives::{BlockNumber, SegmentIndex};
 use subspace_networking::Node;
 use tokio::time::sleep;
 use tracing::{debug, error};
@@ -69,6 +69,7 @@ pub(crate) async fn snap_sync<Backend, Block, AS, Client, PG, NR>(
             import_queue_service.as_mut(),
             &network_request,
             &sync_service,
+            None,
         );
 
         match snap_sync_fut.await {
@@ -95,55 +96,83 @@ pub(crate) async fn snap_sync<Backend, Block, AS, Client, PG, NR>(
         .await;
 }
 
-#[allow(clippy::too_many_arguments)]
-async fn sync<PG, AS, Block, Client, IQS, B, NR>(
+// Get blocks from the last segment or from the segment containing the target block.
+// Returns encoded blocks collection and used segment index.
+pub(crate) async fn get_blocks_from_target_segment<AS, PG>(
     segment_headers_store: &SegmentHeadersStore<AS>,
     node: &Node,
     piece_getter: &PG,
-    fork_id: Option<&str>,
-    client: &Arc<Client>,
-    import_queue_service: &mut IQS,
-    network_request: &NR,
-    sync_service: &SyncingService<Block>,
-) -> Result<(), Error>
+    target_block: Option<BlockNumber>,
+) -> Result<Option<(SegmentIndex, VecDeque<(BlockNumber, Vec<u8>)>)>, Error>
 where
-    B: sc_client_api::Backend<Block>,
-    PG: DsnSyncPieceGetter,
     AS: AuxStore,
-    Block: BlockT,
-    Client: HeaderBackend<Block>
-        + ClientExt<Block, B>
-        + ProvideRuntimeApi<Block>
-        + ProofProvider<Block>
-        + LockImportRun<Block, B>
-        + Send
-        + Sync
-        + 'static,
-    Client::Api: SubspaceApi<Block, FarmerPublicKey> + ObjectsApi<Block>,
-    IQS: ImportQueueService<Block> + ?Sized,
-    NR: NetworkRequest,
+    PG: DsnSyncPieceGetter,
 {
-    debug!("Starting snap sync...");
-
     sync_segment_headers(segment_headers_store, node)
         .await
         .map_err(|error| format!("Failed to sync segment headers: {}", error))?;
 
-    let last_segment_index = segment_headers_store
-        .max_segment_index()
-        .expect("Successfully synced above; qed");
+    let target_segment_index = {
+        let last_segment_index = segment_headers_store
+            .max_segment_index()
+            .expect("Successfully synced above; qed");
+
+        if let Some(target_block) = target_block {
+            let mut segment_header = segment_headers_store
+                .get_segment_header(last_segment_index)
+                .ok_or(format!(
+                    "Can't get segment header from the store: {last_segment_index}"
+                ))?;
+
+            if target_block > segment_header.last_archived_block().number {
+                return Err(format!(
+                    "Target block is greater than the last archived block. \
+                    Last segment index = {last_segment_index}, target block = {target_block}, \
+                    last block from the segment = {}
+                    ",
+                    segment_header.last_archived_block().number
+                )
+                .into());
+            }
+
+            let mut current_segment_index = last_segment_index;
+
+            loop {
+                if current_segment_index <= SegmentIndex::ONE {
+                    break;
+                }
+
+                if target_block > segment_header.last_archived_block().number {
+                    current_segment_index += SegmentIndex::ONE;
+                    break;
+                }
+
+                current_segment_index -= SegmentIndex::ONE;
+
+                segment_header = segment_headers_store
+                    .get_segment_header(current_segment_index)
+                    .ok_or(format!(
+                        "Can't get segment header from the store: {last_segment_index}"
+                    ))?;
+            }
+
+            current_segment_index
+        } else {
+            last_segment_index
+        }
+    };
 
     // Skip the snap sync if there is just one segment header built on top of genesis, it is
     // more efficient to sync it regularly
-    if last_segment_index <= SegmentIndex::ONE {
+    if target_segment_index <= SegmentIndex::ONE {
         debug!("Snap sync was skipped due to too early chain history");
 
-        return Ok(());
+        return Ok(None);
     }
 
     // Identify all segment headers that would need to be reconstructed in order to get first
     // block of last segment header
-    let mut segments_to_reconstruct = VecDeque::from([last_segment_index]);
+    let mut segments_to_reconstruct = VecDeque::from([target_segment_index]);
     {
         let mut last_segment_first_block_number = None;
 
@@ -204,6 +233,56 @@ where
             blocks = VecDeque::from(blocks_fut.await?);
         }
     }
+
+    Ok(Some((target_segment_index, blocks)))
+}
+
+#[allow(clippy::too_many_arguments)]
+/// Synchronize the blockchain to the target_block (approximate value based on the containing
+/// segment) or to the last archived block.
+async fn sync<PG, AS, Block, Client, IQS, B, NR>(
+    segment_headers_store: &SegmentHeadersStore<AS>,
+    node: &Node,
+    piece_getter: &PG,
+    fork_id: Option<&str>,
+    client: &Arc<Client>,
+    import_queue_service: &mut IQS,
+    network_request: &NR,
+    sync_service: &SyncingService<Block>,
+    target_block: Option<BlockNumber>,
+) -> Result<(), Error>
+where
+    B: sc_client_api::Backend<Block>,
+    PG: DsnSyncPieceGetter,
+    AS: AuxStore,
+    Block: BlockT,
+    Client: HeaderBackend<Block>
+        + ClientExt<Block, B>
+        + ProvideRuntimeApi<Block>
+        + ProofProvider<Block>
+        + LockImportRun<Block, B>
+        + Send
+        + Sync
+        + 'static,
+    Client::Api: SubspaceApi<Block, FarmerPublicKey> + ObjectsApi<Block>,
+    IQS: ImportQueueService<Block> + ?Sized,
+    NR: NetworkRequest,
+{
+    debug!("Starting snap sync...");
+
+    let Some((target_segment_index, mut blocks)) =
+        get_blocks_from_target_segment(segment_headers_store, node, piece_getter, target_block)
+            .await?
+    else {
+        // Snap-sync skipped
+        return Ok(());
+    };
+
+    debug!(
+        "Segments data received. Target segment index: {:?}",
+        target_segment_index
+    );
+
     let mut blocks_to_import = Vec::with_capacity(blocks.len());
     let last_block_number;
 
@@ -221,10 +300,10 @@ where
             });
 
         debug!(
-            %last_segment_index,
+            %target_segment_index,
             %first_block_number,
             %last_block_number,
-            "Blocks from last segment downloaded"
+            "Blocks from target segment downloaded"
         );
 
         let signed_block = decode_block::<Block>(&first_block_bytes)
@@ -236,10 +315,10 @@ where
         let state = download_state(&header, client, fork_id, network_request, sync_service)
             .await
             .map_err(|error| {
-                format!("Failed to download state for the first block of last segment: {error}")
+                format!("Failed to download state for the first block of target segment: {error}")
             })?;
 
-        debug!("Downloaded state of the first block of the last segment");
+        debug!("Downloaded state of the first block of the target segment");
 
         blocks_to_import.push(IncomingBlock {
             hash: header.hash(),
@@ -257,7 +336,7 @@ where
 
     debug!(
         blocks_count = %blocks.len(),
-        "Queuing importing remaining blocks from last segment"
+        "Queuing importing remaining blocks from target segment"
     );
 
     for (_block_number, block_bytes) in blocks {
@@ -289,8 +368,8 @@ where
     if let Some(last_block_to_import) = maybe_last_block_to_import {
         debug!(
             %last_block_number,
-            %last_segment_index,
-            "Importing the last block from the last segment"
+            %target_segment_index,
+            "Importing the last block from the target segment"
         );
 
         import_queue_service