Fix selecting shard overlays after decreasing monitor_min_split (#1756)

When node is out of sync (e.g., during initial sync), it may try to use shard overlays that do not exist anymore because monitor min split was decreased.
"Download state", "download archive" and "download proof link" are the types of requests that are necessary to sync.

Author: SpyCheese

validator/full-node.cpp

@@ -444,7 +444,7 @@ void FullNodeImpl::download_zero_state(BlockIdExt id, td::uint32 priority, td::T
 void FullNodeImpl::download_persistent_state(BlockIdExt id, BlockIdExt masterchain_block_id, PersistentStateType type,
                                              td::uint32 priority, td::Timestamp timeout,
                                              td::Promise<td::BufferSlice> promise) {
-  auto shard = get_shard(id.shard_full());
+  auto shard = get_shard(id.shard_full(), /* historical = */ true);
   if (shard.empty()) {
     VLOG(FULL_NODE_WARNING) << "dropping download state diff query to unknown shard";
     promise.set_error(td::Status::Error(ErrorCode::notready, "shard not ready"));
@@ -467,7 +467,7 @@ void FullNodeImpl::download_block_proof(BlockIdExt block_id, td::uint32 priority
 
 void FullNodeImpl::download_block_proof_link(BlockIdExt block_id, td::uint32 priority, td::Timestamp timeout,
                                              td::Promise<td::BufferSlice> promise) {
-  auto shard = get_shard(block_id.shard_full());
+  auto shard = get_shard(block_id.shard_full(), /* historical = */ true);
   if (shard.empty()) {
     VLOG(FULL_NODE_WARNING) << "dropping download proof link query to unknown shard";
     promise.set_error(td::Status::Error(ErrorCode::notready, "shard not ready"));
@@ -490,7 +490,7 @@ void FullNodeImpl::get_next_key_blocks(BlockIdExt block_id, td::Timestamp timeou
 
 void FullNodeImpl::download_archive(BlockSeqno masterchain_seqno, ShardIdFull shard_prefix, std::string tmp_dir,
                       td::Timestamp timeout, td::Promise<std::string> promise) {
-  auto shard = get_shard(shard_prefix);
+  auto shard = get_shard(shard_prefix, /* historical = */ true);
   if (shard.empty()) {
     VLOG(FULL_NODE_WARNING) << "dropping download archive query to unknown shard";
     promise.set_error(td::Status::Error(ErrorCode::notready, "shard not ready"));
@@ -519,16 +519,20 @@ void FullNodeImpl::download_out_msg_queue_proof(ShardIdFull dst_shard, std::vect
                           timeout, std::move(promise));
 }
 
-td::actor::ActorId<FullNodeShard> FullNodeImpl::get_shard(ShardIdFull shard) {
+td::actor::ActorId<FullNodeShard> FullNodeImpl::get_shard(ShardIdFull shard, bool historical) {
   if (shard.is_masterchain()) {
     return shards_[ShardIdFull{masterchainId}].actor.get();
   }
   if (shard.workchain != basechainId) {
     return {};
   }
   int pfx_len = shard.pfx_len();
-  if (pfx_len > wc_monitor_min_split_) {
-    shard = shard_prefix(shard, wc_monitor_min_split_);
+  int min_split = wc_monitor_min_split_;
+  if (historical) {
+    min_split = td::Random::fast(0, min_split);
+  }
+  if (pfx_len > min_split) {
+    shard = shard_prefix(shard, min_split);
   }
   while (true) {
     auto it = shards_.find(shard);

validator/full-node.hpp

@@ -131,7 +131,7 @@ class FullNodeImpl : public FullNode {
   FileHash zero_state_file_hash_;
 
   td::actor::ActorId<FullNodeShard> get_shard(AccountIdPrefixFull dst);
-  td::actor::ActorId<FullNodeShard> get_shard(ShardIdFull shard);
+  td::actor::ActorId<FullNodeShard> get_shard(ShardIdFull shard, bool historical = false);
   std::map<ShardIdFull, ShardInfo> shards_;
   int wc_monitor_min_split_ = 0;