forest/rpc/methods/

chain.rs

// Copyright 2019-2025 ChainSafe Systems
// SPDX-License-Identifier: Apache-2.0, MIT

mod types;
use enumflags2::{BitFlags, make_bitflags};
use types::*;

#[cfg(test)]
use crate::blocks::RawBlockHeader;
use crate::blocks::{Block, CachingBlockHeader, Tipset, TipsetKey};
use crate::chain::index::ResolveNullTipset;
use crate::chain::{ChainStore, ExportOptions, FilecoinSnapshotVersion, HeadChange};
use crate::cid_collections::CidHashSet;
use crate::ipld::DfsIter;
use crate::ipld::{CHAIN_EXPORT_STATUS, cancel_export, end_export, start_export};
use crate::lotus_json::{HasLotusJson, LotusJson, lotus_json_with_self};
#[cfg(test)]
use crate::lotus_json::{assert_all_snapshots, assert_unchanged_via_json};
use crate::message::{ChainMessage, SignedMessage};
use crate::rpc::eth::{EthLog, eth_logs_with_filter, types::ApiHeaders, types::EthFilterSpec};
use crate::rpc::f3::F3ExportLatestSnapshot;
use crate::rpc::types::{ApiExportResult, ApiExportStatus, ApiTipsetKey, Event};
use crate::rpc::{ApiPaths, Ctx, EthEventHandler, Permission, RpcMethod, ServerError};
use crate::shim::clock::ChainEpoch;
use crate::shim::error::ExitCode;
use crate::shim::executor::Receipt;
use crate::shim::message::Message;
use crate::utils::db::CborStoreExt as _;
use crate::utils::io::VoidAsyncWriter;
use anyhow::{Context as _, Result};
use cid::Cid;
use fvm_ipld_blockstore::Blockstore;
use fvm_ipld_encoding::{CborStore, RawBytes};
use hex::ToHex;
use ipld_core::ipld::Ipld;
use jsonrpsee::types::Params;
use jsonrpsee::types::error::ErrorObjectOwned;
use num::BigInt;
use schemars::JsonSchema;
use serde::{Deserialize, Serialize};
use sha2::Sha256;
use std::fs::File;
use std::{
    collections::VecDeque,
    path::PathBuf,
    sync::{Arc, LazyLock},
};
use tokio::sync::{
    Mutex,
    broadcast::{self, Receiver as Subscriber},
};
use tokio::task::JoinHandle;
use tokio_util::sync::CancellationToken;

const HEAD_CHANNEL_CAPACITY: usize = 10;

static CHAIN_EXPORT_LOCK: LazyLock<Mutex<Option<CancellationToken>>> =
    LazyLock::new(|| Mutex::new(None));

/// Subscribes to head changes from the chain store and broadcasts new blocks.
///
/// # Notes
///
/// Spawns an internal `tokio` task that can be aborted anytime via the returned `JoinHandle`,
/// allowing manual cleanup if needed.
pub(crate) fn new_heads<DB: Blockstore>(
    data: &crate::rpc::RPCState<DB>,
) -> (Subscriber<ApiHeaders>, JoinHandle<()>) {
    let (sender, receiver) = broadcast::channel(HEAD_CHANNEL_CAPACITY);

    let mut subscriber = data.chain_store().publisher().subscribe();

    let handle = tokio::spawn(async move {
        while let Ok(v) = subscriber.recv().await {
            let headers = match v {
                HeadChange::Apply(ts) => ApiHeaders(ts.block_headers().clone().into()),
            };
            if let Err(e) = sender.send(headers) {
                tracing::error!("Failed to send headers: {}", e);
                break;
            }
        }
    });

    (receiver, handle)
}

/// Subscribes to head changes from the chain store and broadcasts new `Ethereum` logs.
///
/// # Notes
///
/// Spawns an internal `tokio` task that can be aborted anytime via the returned `JoinHandle`,
/// allowing manual cleanup if needed.
pub(crate) fn logs<DB: Blockstore + Sync + Send + 'static>(
    ctx: &Ctx<DB>,
    filter: Option<EthFilterSpec>,
) -> (Subscriber<Vec<EthLog>>, JoinHandle<()>) {
    let (sender, receiver) = broadcast::channel(HEAD_CHANNEL_CAPACITY);

    let mut subscriber = ctx.chain_store().publisher().subscribe();

    let ctx = ctx.clone();

    let handle = tokio::spawn(async move {
        while let Ok(v) = subscriber.recv().await {
            match v {
                HeadChange::Apply(ts) => {
                    match eth_logs_with_filter(&ctx, &ts, filter.clone(), None).await {
                        Ok(logs) => {
                            if !logs.is_empty()
                                && let Err(e) = sender.send(logs)
                            {
                                tracing::error!(
                                    "Failed to send logs for tipset {}: {}",
                                    ts.key(),
                                    e
                                );
                                break;
                            }
                        }
                        Err(e) => {
                            tracing::error!("Failed to fetch logs for tipset {}: {}", ts.key(), e);
                        }
                    }
                }
            }
        }
    });

    (receiver, handle)
}

pub enum ChainGetFinalizedTipset {}
impl RpcMethod<0> for ChainGetFinalizedTipset {
    const NAME: &'static str = "Filecoin.ChainGetFinalizedTipSet";
    const PARAM_NAMES: [&'static str; 0] = [];
    const API_PATHS: BitFlags<ApiPaths> = make_bitflags!(ApiPaths::V1);
    const PERMISSION: Permission = Permission::Read;
    const DESCRIPTION: Option<&'static str> = Some(
        "Returns the latest F3 finalized tipset, or falls back to EC finality if F3 is not operational on the node or if the F3 finalized tipset is further back than EC finalized tipset.",
    );

    type Params = ();
    type Ok = Arc<Tipset>;

    async fn handle(
        ctx: Ctx<impl Blockstore + Send + Sync + 'static>,
        (): Self::Params,
    ) -> Result<Self::Ok, ServerError> {
        let head = ctx.chain_store().heaviest_tipset();
        let ec_finality_epoch = (head.epoch() - ctx.chain_config().policy.chain_finality).max(0);

        // Either get the f3 finalized tipset or the ec finalized tipset
        match get_f3_finality_tipset(&ctx, ec_finality_epoch).await {
            Ok(f3_tipset) => {
                tracing::debug!("Using F3 finalized tipset at epoch {}", f3_tipset.epoch());
                Ok(f3_tipset)
            }
            Err(_) => {
                // fallback to ec finality
                tracing::warn!("F3 finalization unavailable, falling back to EC finality");
                let ec_tipset = ctx.chain_index().tipset_by_height(
                    ec_finality_epoch,
                    head,
                    ResolveNullTipset::TakeOlder,
                )?;
                Ok(ec_tipset)
            }
        }
    }
}

// get f3 finalized tipset based on ec finality epoch
async fn get_f3_finality_tipset<DB: Blockstore + Sync + Send + 'static>(
    ctx: &Ctx<DB>,
    ec_finality_epoch: ChainEpoch,
) -> Result<Arc<Tipset>> {
    let f3_finalized_cert = crate::rpc::f3::F3GetLatestCertificate::handle(ctx.clone(), ())
        .await
        .map_err(|e| anyhow::anyhow!("Failed to get F3 certificate: {}", e))?;

    let f3_finalized_head = f3_finalized_cert.chain_head();
    if f3_finalized_head.epoch < ec_finality_epoch {
        return Err(anyhow::anyhow!(
            "F3 finalized tipset epoch {} is further back than EC finalized tipset epoch {}",
            f3_finalized_head.epoch,
            ec_finality_epoch
        ));
    }

    ctx.chain_index()
        .load_required_tipset(&f3_finalized_head.key)
        .map_err(|e| {
            anyhow::anyhow!(
                "Failed to load F3 finalized tipset at epoch {}: {}",
                f3_finalized_head.epoch,
                e
            )
        })
}

pub enum ChainGetMessage {}
impl RpcMethod<1> for ChainGetMessage {
    const NAME: &'static str = "Filecoin.ChainGetMessage";
    const PARAM_NAMES: [&'static str; 1] = ["messageCid"];
    const API_PATHS: BitFlags<ApiPaths> = ApiPaths::all();
    const PERMISSION: Permission = Permission::Read;
    const DESCRIPTION: Option<&'static str> = Some("Returns the message with the specified CID.");

    type Params = (Cid,);
    type Ok = Message;

    async fn handle(
        ctx: Ctx<impl Blockstore>,
        (message_cid,): Self::Params,
    ) -> Result<Self::Ok, ServerError> {
        let chain_message: ChainMessage = ctx
            .store()
            .get_cbor(&message_cid)?
            .with_context(|| format!("can't find message with cid {message_cid}"))?;
        Ok(match chain_message {
            ChainMessage::Signed(m) => m.into_message(),
            ChainMessage::Unsigned(m) => m,
        })
    }
}

pub enum ChainGetEvents {}
impl RpcMethod<1> for ChainGetEvents {
    const NAME: &'static str = "Filecoin.ChainGetEvents";
    const PARAM_NAMES: [&'static str; 1] = ["rootCid"];
    const API_PATHS: BitFlags<ApiPaths> = ApiPaths::all();
    const PERMISSION: Permission = Permission::Read;
    const DESCRIPTION: Option<&'static str> =
        Some("Returns the events under the given event AMT root CID.");

    type Params = (Cid,);
    type Ok = Vec<Event>;
    async fn handle(
        ctx: Ctx<impl Blockstore + Send + Sync + 'static>,
        (root_cid,): Self::Params,
    ) -> Result<Self::Ok, ServerError> {
        let tsk = ctx
            .state_manager
            .chain_store()
            .get_tipset_key(&root_cid)?
            .with_context(|| format!("can't find events with cid {root_cid}"))?;

        let ts = ctx.chain_store().load_required_tipset_or_heaviest(&tsk)?;

        let events = EthEventHandler::collect_chain_events(&ctx, &ts, &root_cid).await?;

        Ok(events)
    }
}

pub enum ChainGetParentMessages {}
impl RpcMethod<1> for ChainGetParentMessages {
    const NAME: &'static str = "Filecoin.ChainGetParentMessages";
    const PARAM_NAMES: [&'static str; 1] = ["blockCid"];
    const API_PATHS: BitFlags<ApiPaths> = ApiPaths::all();
    const PERMISSION: Permission = Permission::Read;
    const DESCRIPTION: Option<&'static str> =
        Some("Returns the messages included in the blocks of the parent tipset.");

    type Params = (Cid,);
    type Ok = Vec<ApiMessage>;

    async fn handle(
        ctx: Ctx<impl Blockstore>,
        (block_cid,): Self::Params,
    ) -> Result<Self::Ok, ServerError> {
        let store = ctx.store();
        let block_header: CachingBlockHeader = store
            .get_cbor(&block_cid)?
            .with_context(|| format!("can't find block header with cid {block_cid}"))?;
        if block_header.epoch == 0 {
            Ok(vec![])
        } else {
            let parent_tipset = Tipset::load_required(store, &block_header.parents)?;
            load_api_messages_from_tipset(store, &parent_tipset)
        }
    }
}

pub enum ChainGetParentReceipts {}
impl RpcMethod<1> for ChainGetParentReceipts {
    const NAME: &'static str = "Filecoin.ChainGetParentReceipts";
    const PARAM_NAMES: [&'static str; 1] = ["blockCid"];
    const API_PATHS: BitFlags<ApiPaths> = ApiPaths::all();
    const PERMISSION: Permission = Permission::Read;
    const DESCRIPTION: Option<&'static str> =
        Some("Returns the message receipts included in the blocks of the parent tipset.");

    type Params = (Cid,);
    type Ok = Vec<ApiReceipt>;

    async fn handle(
        ctx: Ctx<impl Blockstore>,
        (block_cid,): Self::Params,
    ) -> Result<Self::Ok, ServerError> {
        let store = ctx.store();
        let block_header: CachingBlockHeader = store
            .get_cbor(&block_cid)?
            .with_context(|| format!("can't find block header with cid {block_cid}"))?;
        if block_header.epoch == 0 {
            return Ok(vec![]);
        }
        let receipts = Receipt::get_receipts(store, block_header.message_receipts)
            .map_err(|_| {
                ErrorObjectOwned::owned::<()>(
                    1,
                    format!(
                        "failed to root: ipld: could not find {}",
                        block_header.message_receipts
                    ),
                    None,
                )
            })?
            .iter()
            .map(|r| ApiReceipt {
                exit_code: r.exit_code().into(),
                return_data: r.return_data(),
                gas_used: r.gas_used(),
                events_root: r.events_root(),
            })
            .collect();

        Ok(receipts)
    }
}

pub enum ChainGetMessagesInTipset {}
impl RpcMethod<1> for ChainGetMessagesInTipset {
    const NAME: &'static str = "Filecoin.ChainGetMessagesInTipset";
    const PARAM_NAMES: [&'static str; 1] = ["tipsetKey"];
    const API_PATHS: BitFlags<ApiPaths> = ApiPaths::all();
    const PERMISSION: Permission = Permission::Read;

    type Params = (ApiTipsetKey,);
    type Ok = Vec<ApiMessage>;

    async fn handle(
        ctx: Ctx<impl Blockstore>,
        (ApiTipsetKey(tipset_key),): Self::Params,
    ) -> Result<Self::Ok, ServerError> {
        let tipset = ctx
            .chain_store()
            .load_required_tipset_or_heaviest(&tipset_key)?;
        load_api_messages_from_tipset(ctx.store(), &tipset)
    }
}

pub enum ChainPruneSnapshot {}
impl RpcMethod<1> for ChainPruneSnapshot {
    const NAME: &'static str = "Forest.SnapshotGC";
    const PARAM_NAMES: [&'static str; 1] = ["blocking"];
    const API_PATHS: BitFlags<ApiPaths> = ApiPaths::all();
    const PERMISSION: Permission = Permission::Admin;

    type Params = (bool,);
    type Ok = ();

    async fn handle(
        _ctx: Ctx<impl Blockstore + Send + Sync + 'static>,
        (blocking,): Self::Params,
    ) -> Result<Self::Ok, ServerError> {
        if let Some(gc) = crate::daemon::GLOBAL_SNAPSHOT_GC.get() {
            let progress_rx = gc.trigger()?;
            while blocking && progress_rx.recv_async().await.is_ok() {}
            Ok(())
        } else {
            Err(anyhow::anyhow!("snapshot gc is not enabled").into())
        }
    }
}

pub enum ForestChainExport {}
impl RpcMethod<1> for ForestChainExport {
    const NAME: &'static str = "Forest.ChainExport";
    const PARAM_NAMES: [&'static str; 1] = ["params"];
    const API_PATHS: BitFlags<ApiPaths> = ApiPaths::all();
    const PERMISSION: Permission = Permission::Read;

    type Params = (ForestChainExportParams,);
    type Ok = ApiExportResult;

    async fn handle(
        ctx: Ctx<impl Blockstore + Send + Sync + 'static>,
        (params,): Self::Params,
    ) -> Result<Self::Ok, ServerError> {
        let ForestChainExportParams {
            version,
            epoch,
            recent_roots,
            output_path,
            tipset_keys: ApiTipsetKey(tsk),
            skip_checksum,
            dry_run,
        } = params;

        let token = CancellationToken::new();
        {
            let mut guard = CHAIN_EXPORT_LOCK.lock().await;
            if guard.is_some() {
                return Err(
                    anyhow::anyhow!("A chain export is still in progress. Cancel it with the export-cancel subcommand if needed.").into(),
                );
            }
            *guard = Some(token.clone());
        }
        start_export();

        let head = ctx.chain_store().load_required_tipset_or_heaviest(&tsk)?;
        let start_ts =
            ctx.chain_index()
                .tipset_by_height(epoch, head, ResolveNullTipset::TakeOlder)?;

        let options = Some(ExportOptions {
            skip_checksum,
            seen: Default::default(),
        });
        let writer = if dry_run {
            tokio_util::either::Either::Left(VoidAsyncWriter)
        } else {
            tokio_util::either::Either::Right(tokio::fs::File::create(&output_path).await?)
        };
        let result = match version {
            FilecoinSnapshotVersion::V1 => {
                let db = ctx.store_owned();

                let chain_export =
                    crate::chain::export::<Sha256>(&db, &start_ts, recent_roots, writer, options);

                tokio::select! {
                    result = chain_export => {
                        result.map(|checksum_opt| ApiExportResult::Done(checksum_opt.map(|hash| hash.encode_hex())))
                    },
                    _ = token.cancelled() => {
                        cancel_export();
                        tracing::warn!("Snapshot export was cancelled");
                        Ok(ApiExportResult::Cancelled)
                    },
                }
            }
            FilecoinSnapshotVersion::V2 => {
                let db = ctx.store_owned();

                let f3_snap_tmp_path = {
                    let mut f3_snap_dir = output_path.clone();
                    let mut builder = tempfile::Builder::new();
                    let with_suffix = builder.suffix(".f3snap.bin");
                    if f3_snap_dir.pop() {
                        with_suffix.tempfile_in(&f3_snap_dir)
                    } else {
                        with_suffix.tempfile_in(".")
                    }?
                    .into_temp_path()
                };
                let f3_snap = {
                    match F3ExportLatestSnapshot::run(f3_snap_tmp_path.display().to_string()).await
                    {
                        Ok(cid) => Some((cid, File::open(&f3_snap_tmp_path)?)),
                        Err(e) => {
                            tracing::error!("Failed to export F3 snapshot: {e}");
                            None
                        }
                    }
                };

                let chain_export = crate::chain::export_v2::<Sha256, _>(
                    &db,
                    f3_snap,
                    &start_ts,
                    recent_roots,
                    writer,
                    options,
                );

                tokio::select! {
                    result = chain_export => {
                        result.map(|checksum_opt| ApiExportResult::Done(checksum_opt.map(|hash| hash.encode_hex())))
                    },
                    _ = token.cancelled() => {
                        cancel_export();
                        tracing::warn!("Snapshot export was cancelled");
                        Ok(ApiExportResult::Cancelled)
                    },
                }
            }
        };
        end_export();
        // Clean up token
        let mut guard = CHAIN_EXPORT_LOCK.lock().await;
        *guard = None;
        match result {
            Ok(export_result) => Ok(export_result),
            Err(e) => Err(anyhow::anyhow!(e).into()),
        }
    }
}

pub enum ForestChainExportStatus {}
impl RpcMethod<0> for ForestChainExportStatus {
    const NAME: &'static str = "Forest.ChainExportStatus";
    const PARAM_NAMES: [&'static str; 0] = [];
    const API_PATHS: BitFlags<ApiPaths> = ApiPaths::all();
    const PERMISSION: Permission = Permission::Read;

    type Params = ();
    type Ok = ApiExportStatus;

    async fn handle(_ctx: Ctx<impl Blockstore>, (): Self::Params) -> Result<Self::Ok, ServerError> {
        let mutex = CHAIN_EXPORT_STATUS.lock();

        let progress = if mutex.initial_epoch == 0 {
            0.0
        } else {
            let p = 1.0 - ((mutex.epoch as f64) / (mutex.initial_epoch as f64));
            if p.is_finite() {
                p.clamp(0.0, 1.0)
            } else {
                0.0
            }
        };
        // only two decimal places
        let progress = (progress * 100.0).round() / 100.0;

        let status = ApiExportStatus {
            progress,
            exporting: mutex.exporting,
            cancelled: mutex.cancelled,
            start_time: mutex.start_time,
        };

        Ok(status)
    }
}

pub enum ForestChainExportCancel {}
impl RpcMethod<0> for ForestChainExportCancel {
    const NAME: &'static str = "Forest.ChainExportCancel";
    const PARAM_NAMES: [&'static str; 0] = [];
    const API_PATHS: BitFlags<ApiPaths> = ApiPaths::all();
    const PERMISSION: Permission = Permission::Read;

    type Params = ();
    type Ok = bool;

    async fn handle(_ctx: Ctx<impl Blockstore>, (): Self::Params) -> Result<Self::Ok, ServerError> {
        if let Some(token) = CHAIN_EXPORT_LOCK.lock().await.as_ref() {
            token.cancel();
            return Ok(true);
        }

        Ok(false)
    }
}

pub enum ForestChainExportDiff {}
impl RpcMethod<1> for ForestChainExportDiff {
    const NAME: &'static str = "Forest.ChainExportDiff";
    const PARAM_NAMES: [&'static str; 1] = ["params"];
    const API_PATHS: BitFlags<ApiPaths> = ApiPaths::all();
    const PERMISSION: Permission = Permission::Read;

    type Params = (ForestChainExportDiffParams,);
    type Ok = ();

    async fn handle(
        ctx: Ctx<impl Blockstore + Send + Sync + 'static>,
        (params,): Self::Params,
    ) -> Result<Self::Ok, ServerError> {
        let ForestChainExportDiffParams {
            from,
            to,
            depth,
            output_path,
        } = params;

        let _locked = CHAIN_EXPORT_LOCK.try_lock();
        if _locked.is_err() {
            return Err(
                anyhow::anyhow!("Another chain export diff job is still in progress").into(),
            );
        }

        let chain_finality = ctx.chain_config().policy.chain_finality;
        if depth < chain_finality {
            return Err(
                anyhow::anyhow!(format!("depth must be greater than {chain_finality}")).into(),
            );
        }

        let head = ctx.chain_store().heaviest_tipset();
        let start_ts =
            ctx.chain_index()
                .tipset_by_height(from, head, ResolveNullTipset::TakeOlder)?;

        crate::tool::subcommands::archive_cmd::do_export(
            &ctx.store_owned(),
            start_ts,
            output_path,
            None,
            depth,
            Some(to),
            Some(chain_finality),
            true,
        )
        .await?;

        Ok(())
    }
}

pub enum ChainExport {}
impl RpcMethod<1> for ChainExport {
    const NAME: &'static str = "Filecoin.ChainExport";
    const PARAM_NAMES: [&'static str; 1] = ["params"];
    const API_PATHS: BitFlags<ApiPaths> = ApiPaths::all();
    const PERMISSION: Permission = Permission::Read;

    type Params = (ChainExportParams,);
    type Ok = ApiExportResult;

    async fn handle(
        ctx: Ctx<impl Blockstore + Send + Sync + 'static>,
        (ChainExportParams {
            epoch,
            recent_roots,
            output_path,
            tipset_keys,
            skip_checksum,
            dry_run,
        },): Self::Params,
    ) -> Result<Self::Ok, ServerError> {
        ForestChainExport::handle(
            ctx,
            (ForestChainExportParams {
                version: FilecoinSnapshotVersion::V1,
                epoch,
                recent_roots,
                output_path,
                tipset_keys,
                skip_checksum,
                dry_run,
            },),
        )
        .await
    }
}

pub enum ChainReadObj {}
impl RpcMethod<1> for ChainReadObj {
    const NAME: &'static str = "Filecoin.ChainReadObj";
    const PARAM_NAMES: [&'static str; 1] = ["cid"];
    const API_PATHS: BitFlags<ApiPaths> = ApiPaths::all();
    const PERMISSION: Permission = Permission::Read;
    const DESCRIPTION: Option<&'static str> = Some(
        "Reads IPLD nodes referenced by the specified CID from the chain blockstore and returns raw bytes.",
    );

    type Params = (Cid,);
    type Ok = Vec<u8>;

    async fn handle(
        ctx: Ctx<impl Blockstore>,
        (cid,): Self::Params,
    ) -> Result<Self::Ok, ServerError> {
        let bytes = ctx
            .store()
            .get(&cid)?
            .with_context(|| format!("can't find object with cid={cid}"))?;
        Ok(bytes)
    }
}

pub enum ChainHasObj {}
impl RpcMethod<1> for ChainHasObj {
    const NAME: &'static str = "Filecoin.ChainHasObj";
    const PARAM_NAMES: [&'static str; 1] = ["cid"];
    const API_PATHS: BitFlags<ApiPaths> = ApiPaths::all();
    const PERMISSION: Permission = Permission::Read;
    const DESCRIPTION: Option<&'static str> =
        Some("Checks if a given CID exists in the chain blockstore.");

    type Params = (Cid,);
    type Ok = bool;

    async fn handle(
        ctx: Ctx<impl Blockstore>,
        (cid,): Self::Params,
    ) -> Result<Self::Ok, ServerError> {
        Ok(ctx.store().get(&cid)?.is_some())
    }
}

/// Returns statistics about the graph referenced by 'obj'.
/// If 'base' is also specified, then the returned stat will be a diff between the two objects.
pub enum ChainStatObj {}
impl RpcMethod<2> for ChainStatObj {
    const NAME: &'static str = "Filecoin.ChainStatObj";
    const PARAM_NAMES: [&'static str; 2] = ["obj_cid", "base_cid"];
    const API_PATHS: BitFlags<ApiPaths> = ApiPaths::all();
    const PERMISSION: Permission = Permission::Read;

    type Params = (Cid, Option<Cid>);
    type Ok = ObjStat;

    async fn handle(
        ctx: Ctx<impl Blockstore>,
        (obj_cid, base_cid): Self::Params,
    ) -> Result<Self::Ok, ServerError> {
        let mut stats = ObjStat::default();
        let mut seen = CidHashSet::default();
        let mut walk = |cid, collect| {
            let mut queue = VecDeque::new();
            queue.push_back(cid);
            while let Some(link_cid) = queue.pop_front() {
                if !seen.insert(link_cid) {
                    continue;
                }
                let data = ctx.store().get(&link_cid)?;
                if let Some(data) = data {
                    if collect {
                        stats.links += 1;
                        stats.size += data.len();
                    }
                    if matches!(link_cid.codec(), fvm_ipld_encoding::DAG_CBOR)
                        && let Ok(ipld) =
                            crate::utils::encoding::from_slice_with_fallback::<Ipld>(&data)
                    {
                        for ipld in DfsIter::new(ipld) {
                            if let Ipld::Link(cid) = ipld {
                                queue.push_back(cid);
                            }
                        }
                    }
                }
            }
            anyhow::Ok(())
        };
        if let Some(base_cid) = base_cid {
            walk(base_cid, false)?;
        }
        walk(obj_cid, true)?;
        Ok(stats)
    }
}

pub enum ChainGetBlockMessages {}
impl RpcMethod<1> for ChainGetBlockMessages {
    const NAME: &'static str = "Filecoin.ChainGetBlockMessages";
    const PARAM_NAMES: [&'static str; 1] = ["blockCid"];
    const API_PATHS: BitFlags<ApiPaths> = ApiPaths::all();
    const PERMISSION: Permission = Permission::Read;
    const DESCRIPTION: Option<&'static str> =
        Some("Returns all messages from the specified block.");

    type Params = (Cid,);
    type Ok = BlockMessages;

    async fn handle(
        ctx: Ctx<impl Blockstore>,
        (block_cid,): Self::Params,
    ) -> Result<Self::Ok, ServerError> {
        let blk: CachingBlockHeader = ctx.store().get_cbor_required(&block_cid)?;
        let (unsigned_cids, signed_cids) = crate::chain::read_msg_cids(ctx.store(), &blk)?;
        let (bls_msg, secp_msg) =
            crate::chain::block_messages_from_cids(ctx.store(), &unsigned_cids, &signed_cids)?;
        let cids = unsigned_cids.into_iter().chain(signed_cids).collect();

        let ret = BlockMessages {
            bls_msg,
            secp_msg,
            cids,
        };
        Ok(ret)
    }
}

pub enum ChainGetPath {}
impl RpcMethod<2> for ChainGetPath {
    const NAME: &'static str = "Filecoin.ChainGetPath";
    const PARAM_NAMES: [&'static str; 2] = ["from", "to"];
    const API_PATHS: BitFlags<ApiPaths> = ApiPaths::all();
    const PERMISSION: Permission = Permission::Read;
    const DESCRIPTION: Option<&'static str> =
        Some("Returns the path between the two specified tipsets.");

    type Params = (TipsetKey, TipsetKey);
    type Ok = Vec<PathChange>;

    async fn handle(
        ctx: Ctx<impl Blockstore>,
        (from, to): Self::Params,
    ) -> Result<Self::Ok, ServerError> {
        impl_chain_get_path(ctx.chain_store(), &from, &to).map_err(Into::into)
    }
}

/// Find the path between two tipsets, as a series of [`PathChange`]s.
///
/// ```text
/// 0 - A - B - C - D
///     ^~~~~~~~> apply B, C
///
/// 0 - A - B - C - D
///     <~~~~~~~^ revert C, B
///
///     <~~~~~~~~ revert C, B
/// 0 - A - B  - C
///     |
///      -- B' - C'
///      ~~~~~~~~> then apply B', C'
/// ```
///
/// Exposes errors from the [`Blockstore`], and returns an error if there is no common ancestor.
fn impl_chain_get_path(
    chain_store: &ChainStore<impl Blockstore>,
    from: &TipsetKey,
    to: &TipsetKey,
) -> anyhow::Result<Vec<PathChange>> {
    let mut to_revert = chain_store
        .load_required_tipset_or_heaviest(from)
        .context("couldn't load `from`")?;
    let mut to_apply = chain_store
        .load_required_tipset_or_heaviest(to)
        .context("couldn't load `to`")?;

    let mut all_reverts = vec![];
    let mut all_applies = vec![];

    // This loop is guaranteed to terminate if the blockstore contain no cycles.
    // This is currently computationally infeasible.
    while to_revert != to_apply {
        if to_revert.epoch() > to_apply.epoch() {
            let next = chain_store
                .load_required_tipset_or_heaviest(to_revert.parents())
                .context("couldn't load ancestor of `from`")?;
            all_reverts.push(to_revert);
            to_revert = next;
        } else {
            let next = chain_store
                .load_required_tipset_or_heaviest(to_apply.parents())
                .context("couldn't load ancestor of `to`")?;
            all_applies.push(to_apply);
            to_apply = next;
        }
    }
    Ok(all_reverts
        .into_iter()
        .map(PathChange::Revert)
        .chain(all_applies.into_iter().rev().map(PathChange::Apply))
        .collect())
}

/// Get tipset at epoch. Pick younger tipset if epoch points to a
/// null-tipset. Only tipsets below the given `head` are searched. If `head`
/// is null, the node will use the heaviest tipset.
pub enum ChainGetTipSetByHeight {}
impl RpcMethod<2> for ChainGetTipSetByHeight {
    const NAME: &'static str = "Filecoin.ChainGetTipSetByHeight";
    const PARAM_NAMES: [&'static str; 2] = ["height", "tipsetKey"];
    const API_PATHS: BitFlags<ApiPaths> = ApiPaths::all();
    const PERMISSION: Permission = Permission::Read;
    const DESCRIPTION: Option<&'static str> = Some("Returns the tipset at the specified height.");

    type Params = (ChainEpoch, ApiTipsetKey);
    type Ok = Arc<Tipset>;

    async fn handle(
        ctx: Ctx<impl Blockstore>,
        (height, ApiTipsetKey(tipset_key)): Self::Params,
    ) -> Result<Self::Ok, ServerError> {
        let ts = ctx
            .chain_store()
            .load_required_tipset_or_heaviest(&tipset_key)?;
        let tss = ctx
            .chain_index()
            .tipset_by_height(height, ts, ResolveNullTipset::TakeOlder)?;
        Ok(tss)
    }
}

pub enum ChainGetTipSetAfterHeight {}
impl RpcMethod<2> for ChainGetTipSetAfterHeight {
    const NAME: &'static str = "Filecoin.ChainGetTipSetAfterHeight";
    const PARAM_NAMES: [&'static str; 2] = ["height", "tipsetKey"];
    const API_PATHS: BitFlags<ApiPaths> = ApiPaths::all();
    const PERMISSION: Permission = Permission::Read;
    const DESCRIPTION: Option<&'static str> = Some(
        "Looks back and returns the tipset at the specified epoch.
    If there are no blocks at the given epoch,
    returns the first non-nil tipset at a later epoch.",
    );

    type Params = (ChainEpoch, ApiTipsetKey);
    type Ok = Arc<Tipset>;

    async fn handle(
        ctx: Ctx<impl Blockstore>,
        (height, ApiTipsetKey(tipset_key)): Self::Params,
    ) -> Result<Self::Ok, ServerError> {
        let ts = ctx
            .chain_store()
            .load_required_tipset_or_heaviest(&tipset_key)?;
        let tss = ctx
            .chain_index()
            .tipset_by_height(height, ts, ResolveNullTipset::TakeNewer)?;
        Ok(tss)
    }
}

pub enum ChainGetGenesis {}
impl RpcMethod<0> for ChainGetGenesis {
    const NAME: &'static str = "Filecoin.ChainGetGenesis";
    const PARAM_NAMES: [&'static str; 0] = [];
    const API_PATHS: BitFlags<ApiPaths> = ApiPaths::all();
    const PERMISSION: Permission = Permission::Read;

    type Params = ();
    type Ok = Option<Tipset>;

    async fn handle(ctx: Ctx<impl Blockstore>, (): Self::Params) -> Result<Self::Ok, ServerError> {
        let genesis = ctx.chain_store().genesis_block_header();
        Ok(Some(Tipset::from(genesis)))
    }
}

pub enum ChainHead {}
impl RpcMethod<0> for ChainHead {
    const NAME: &'static str = "Filecoin.ChainHead";
    const PARAM_NAMES: [&'static str; 0] = [];
    const API_PATHS: BitFlags<ApiPaths> = ApiPaths::all();
    const PERMISSION: Permission = Permission::Read;
    const DESCRIPTION: Option<&'static str> = Some("Returns the chain head (heaviest tipset).");

    type Params = ();
    type Ok = Arc<Tipset>;

    async fn handle(ctx: Ctx<impl Blockstore>, (): Self::Params) -> Result<Self::Ok, ServerError> {
        let heaviest = ctx.chain_store().heaviest_tipset();
        Ok(heaviest)
    }
}

pub enum ChainGetBlock {}
impl RpcMethod<1> for ChainGetBlock {
    const NAME: &'static str = "Filecoin.ChainGetBlock";
    const PARAM_NAMES: [&'static str; 1] = ["blockCid"];
    const API_PATHS: BitFlags<ApiPaths> = ApiPaths::all();
    const PERMISSION: Permission = Permission::Read;
    const DESCRIPTION: Option<&'static str> = Some("Returns the block with the specified CID.");

    type Params = (Cid,);
    type Ok = CachingBlockHeader;

    async fn handle(
        ctx: Ctx<impl Blockstore>,
        (block_cid,): Self::Params,
    ) -> Result<Self::Ok, ServerError> {
        let blk: CachingBlockHeader = ctx.store().get_cbor_required(&block_cid)?;
        Ok(blk)
    }
}

pub enum ChainGetTipSet {}
impl RpcMethod<1> for ChainGetTipSet {
    const NAME: &'static str = "Filecoin.ChainGetTipSet";
    const PARAM_NAMES: [&'static str; 1] = ["tipsetKey"];
    const API_PATHS: BitFlags<ApiPaths> = make_bitflags!(ApiPaths::{ V0 | V1 });
    const PERMISSION: Permission = Permission::Read;
    const DESCRIPTION: Option<&'static str> = Some("Returns the tipset with the specified CID.");

    type Params = (ApiTipsetKey,);
    type Ok = Arc<Tipset>;

    async fn handle(
        ctx: Ctx<impl Blockstore>,
        (ApiTipsetKey(tipset_key),): Self::Params,
    ) -> Result<Self::Ok, ServerError> {
        let ts = ctx
            .chain_store()
            .load_required_tipset_or_heaviest(&tipset_key)?;
        Ok(ts)
    }
}

pub enum ChainGetTipSetV2 {}
impl RpcMethod<1> for ChainGetTipSetV2 {
    const NAME: &'static str = "Filecoin.ChainGetTipSet";
    const PARAM_NAMES: [&'static str; 1] = ["tipsetSelector"];
    const API_PATHS: BitFlags<ApiPaths> = make_bitflags!(ApiPaths::{ V2 });
    const PERMISSION: Permission = Permission::Read;
    const DESCRIPTION: Option<&'static str> = Some("Returns the tipset with the specified CID.");

    type Params = (ApiTipsetKey,);
    type Ok = Arc<Tipset>;

    async fn handle(_: Ctx<impl Blockstore>, _: Self::Params) -> Result<Self::Ok, ServerError> {
        Err(ServerError::unsupported_method())
    }
}

pub enum ChainSetHead {}
impl RpcMethod<1> for ChainSetHead {
    const NAME: &'static str = "Filecoin.ChainSetHead";
    const PARAM_NAMES: [&'static str; 1] = ["tsk"];
    const API_PATHS: BitFlags<ApiPaths> = ApiPaths::all();
    const PERMISSION: Permission = Permission::Admin;

    type Params = (TipsetKey,);
    type Ok = ();

    async fn handle(
        ctx: Ctx<impl Blockstore>,
        (tsk,): Self::Params,
    ) -> Result<Self::Ok, ServerError> {
        // This is basically a port of the reference implementation at
        // https://github.com/filecoin-project/lotus/blob/v1.23.0/node/impl/full/chain.go#L321

        let new_head = ctx.chain_index().load_required_tipset(&tsk)?;
        let mut current = ctx.chain_store().heaviest_tipset();
        while current.epoch() >= new_head.epoch() {
            for cid in current.key().to_cids() {
                ctx.chain_store().unmark_block_as_validated(&cid);
            }
            let parents = &current.block_headers().first().parents;
            current = ctx.chain_index().load_required_tipset(parents)?;
        }
        ctx.chain_store()
            .set_heaviest_tipset(new_head)
            .map_err(Into::into)
    }
}

pub enum ChainGetMinBaseFee {}
impl RpcMethod<1> for ChainGetMinBaseFee {
    const NAME: &'static str = "Forest.ChainGetMinBaseFee";
    const PARAM_NAMES: [&'static str; 1] = ["lookback"];
    const API_PATHS: BitFlags<ApiPaths> = ApiPaths::all();
    const PERMISSION: Permission = Permission::Read;

    type Params = (u32,);
    type Ok = String;

    async fn handle(
        ctx: Ctx<impl Blockstore>,
        (lookback,): Self::Params,
    ) -> Result<Self::Ok, ServerError> {
        let mut current = ctx.chain_store().heaviest_tipset();
        let mut min_base_fee = current.block_headers().first().parent_base_fee.clone();

        for _ in 0..lookback {
            let parents = &current.block_headers().first().parents;
            current = ctx.chain_index().load_required_tipset(parents)?;

            min_base_fee =
                min_base_fee.min(current.block_headers().first().parent_base_fee.to_owned());
        }

        Ok(min_base_fee.atto().to_string())
    }
}

pub enum ChainTipSetWeight {}
impl RpcMethod<1> for ChainTipSetWeight {
    const NAME: &'static str = "Filecoin.ChainTipSetWeight";
    const PARAM_NAMES: [&'static str; 1] = ["tipsetKey"];
    const API_PATHS: BitFlags<ApiPaths> = ApiPaths::all();
    const PERMISSION: Permission = Permission::Read;
    const DESCRIPTION: Option<&'static str> = Some("Returns the weight of the specified tipset.");

    type Params = (ApiTipsetKey,);
    type Ok = BigInt;

    async fn handle(
        ctx: Ctx<impl Blockstore>,
        (ApiTipsetKey(tipset_key),): Self::Params,
    ) -> Result<Self::Ok, ServerError> {
        let ts = ctx
            .chain_store()
            .load_required_tipset_or_heaviest(&tipset_key)?;
        let weight = crate::fil_cns::weight(ctx.store(), &ts)?;
        Ok(weight)
    }
}

pub const CHAIN_NOTIFY: &str = "Filecoin.ChainNotify";
pub(crate) fn chain_notify<DB: Blockstore>(
    _params: Params<'_>,
    data: &crate::rpc::RPCState<DB>,
) -> Subscriber<Vec<ApiHeadChange>> {
    let (sender, receiver) = broadcast::channel(HEAD_CHANNEL_CAPACITY);

    // As soon as the channel is created, send the current tipset
    let current = data.chain_store().heaviest_tipset();
    let (change, tipset) = ("current".into(), current);
    sender
        .send(vec![ApiHeadChange { change, tipset }])
        .expect("receiver is not dropped");

    let mut subscriber = data.chain_store().publisher().subscribe();

    tokio::spawn(async move {
        // Skip first message
        let _ = subscriber.recv().await;

        while let Ok(v) = subscriber.recv().await {
            let (change, tipset) = match v {
                HeadChange::Apply(ts) => ("apply".into(), ts),
            };

            if sender.send(vec![ApiHeadChange { change, tipset }]).is_err() {
                break;
            }
        }
    });
    receiver
}

fn load_api_messages_from_tipset(
    store: &impl Blockstore,
    tipset: &Tipset,
) -> Result<Vec<ApiMessage>, ServerError> {
    let full_tipset = tipset
        .fill_from_blockstore(store)
        .context("Failed to load full tipset")?;
    let blocks = full_tipset.into_blocks();
    let mut messages = vec![];
    let mut seen = CidHashSet::default();
    for Block {
        bls_messages,
        secp_messages,
        ..
    } in blocks
    {
        for message in bls_messages {
            let cid = message.cid();
            if seen.insert(cid) {
                messages.push(ApiMessage { cid, message });
            }
        }

        for msg in secp_messages {
            let cid = msg.cid();
            if seen.insert(cid) {
                messages.push(ApiMessage {
                    cid,
                    message: msg.message,
                });
            }
        }
    }

    Ok(messages)
}

#[derive(Debug, Clone, PartialEq, Serialize, Deserialize, JsonSchema)]
pub struct BlockMessages {
    #[serde(rename = "BlsMessages", with = "crate::lotus_json")]
    #[schemars(with = "LotusJson<Vec<Message>>")]
    pub bls_msg: Vec<Message>,
    #[serde(rename = "SecpkMessages", with = "crate::lotus_json")]
    #[schemars(with = "LotusJson<Vec<SignedMessage>>")]
    pub secp_msg: Vec<SignedMessage>,
    #[serde(rename = "Cids", with = "crate::lotus_json")]
    #[schemars(with = "LotusJson<Vec<Cid>>")]
    pub cids: Vec<Cid>,
}
lotus_json_with_self!(BlockMessages);

#[derive(Debug, Clone, Serialize, Deserialize, Eq, PartialEq, JsonSchema)]
#[serde(rename_all = "PascalCase")]
pub struct ApiReceipt {
    // Exit status of message execution
    pub exit_code: ExitCode,
    // `Return` value if the exit code is zero
    #[serde(rename = "Return", with = "crate::lotus_json")]
    #[schemars(with = "LotusJson<RawBytes>")]
    pub return_data: RawBytes,
    // Non-negative value of GasUsed
    pub gas_used: u64,
    #[serde(with = "crate::lotus_json")]
    #[schemars(with = "LotusJson<Option<Cid>>")]
    pub events_root: Option<Cid>,
}

lotus_json_with_self!(ApiReceipt);

#[derive(Serialize, Deserialize, JsonSchema, Clone, Debug, Eq, PartialEq)]
#[serde(rename_all = "PascalCase")]
pub struct ApiMessage {
    #[serde(with = "crate::lotus_json")]
    #[schemars(with = "LotusJson<Cid>")]
    pub cid: Cid,
    #[serde(with = "crate::lotus_json")]
    #[schemars(with = "LotusJson<Message>")]
    pub message: Message,
}

lotus_json_with_self!(ApiMessage);

#[derive(Debug, Clone, Serialize, Deserialize, JsonSchema)]
pub struct ForestChainExportParams {
    pub version: FilecoinSnapshotVersion,
    pub epoch: ChainEpoch,
    pub recent_roots: i64,
    pub output_path: PathBuf,
    #[schemars(with = "LotusJson<ApiTipsetKey>")]
    #[serde(with = "crate::lotus_json")]
    pub tipset_keys: ApiTipsetKey,
    pub skip_checksum: bool,
    pub dry_run: bool,
}
lotus_json_with_self!(ForestChainExportParams);

#[derive(Debug, Clone, Serialize, Deserialize, JsonSchema)]
pub struct ForestChainExportDiffParams {
    pub from: ChainEpoch,
    pub to: ChainEpoch,
    pub depth: i64,
    pub output_path: PathBuf,
}
lotus_json_with_self!(ForestChainExportDiffParams);

#[derive(Debug, Clone, Serialize, Deserialize, JsonSchema)]
pub struct ChainExportParams {
    pub epoch: ChainEpoch,
    pub recent_roots: i64,
    pub output_path: PathBuf,
    #[schemars(with = "LotusJson<ApiTipsetKey>")]
    #[serde(with = "crate::lotus_json")]
    pub tipset_keys: ApiTipsetKey,
    pub skip_checksum: bool,
    pub dry_run: bool,
}
lotus_json_with_self!(ChainExportParams);

#[derive(PartialEq, Debug, Serialize, Deserialize, Clone, JsonSchema)]
#[serde(rename_all = "PascalCase")]
pub struct ApiHeadChange {
    #[serde(rename = "Type")]
    pub change: String,
    #[serde(rename = "Val", with = "crate::lotus_json")]
    #[schemars(with = "LotusJson<Tipset>")]
    pub tipset: Arc<Tipset>,
}
lotus_json_with_self!(ApiHeadChange);

#[derive(PartialEq, Debug, Serialize, Deserialize, Clone, JsonSchema)]
#[serde(tag = "Type", content = "Val", rename_all = "snake_case")]
pub enum PathChange<T = Arc<Tipset>> {
    Revert(T),
    Apply(T),
}
impl HasLotusJson for PathChange {
    type LotusJson = PathChange<<Tipset as HasLotusJson>::LotusJson>;

    #[cfg(test)]
    fn snapshots() -> Vec<(serde_json::Value, Self)> {
        use serde_json::json;
        vec![(
            json!({
                "Type": "revert",
                "Val": {
                    "Blocks": [
                        {
                            "BeaconEntries": null,
                            "ForkSignaling": 0,
                            "Height": 0,
                            "Messages": { "/": "baeaaaaa" },
                            "Miner": "f00",
                            "ParentBaseFee": "0",
                            "ParentMessageReceipts": { "/": "baeaaaaa" },
                            "ParentStateRoot": { "/":"baeaaaaa" },
                            "ParentWeight": "0",
                            "Parents": [{"/":"bafyreiaqpwbbyjo4a42saasj36kkrpv4tsherf2e7bvezkert2a7dhonoi"}],
                            "Timestamp": 0,
                            "WinPoStProof": null
                        }
                    ],
                    "Cids": [
                        { "/": "bafy2bzaceag62hjj3o43lf6oyeox3fvg5aqkgl5zagbwpjje3ajwg6yw4iixk" }
                    ],
                    "Height": 0
                }
            }),
            Self::Revert(Arc::new(Tipset::from(RawBlockHeader::default()))),
        )]
    }

    fn into_lotus_json(self) -> Self::LotusJson {
        match self {
            PathChange::Revert(it) => {
                PathChange::Revert(Arc::unwrap_or_clone(it).into_lotus_json())
            }
            PathChange::Apply(it) => PathChange::Apply(Arc::unwrap_or_clone(it).into_lotus_json()),
        }
    }

    fn from_lotus_json(lotus_json: Self::LotusJson) -> Self {
        match lotus_json {
            PathChange::Revert(it) => PathChange::Revert(Tipset::from_lotus_json(it).into()),
            PathChange::Apply(it) => PathChange::Apply(Tipset::from_lotus_json(it).into()),
        }
    }
}

#[cfg(test)]
impl<T> quickcheck::Arbitrary for PathChange<T>
where
    T: quickcheck::Arbitrary,
{
    fn arbitrary(g: &mut quickcheck::Gen) -> Self {
        let inner = T::arbitrary(g);
        g.choose(&[PathChange::Apply(inner.clone()), PathChange::Revert(inner)])
            .unwrap()
            .clone()
    }
}

#[test]
fn snapshots() {
    assert_all_snapshots::<PathChange>()
}

#[cfg(test)]
quickcheck::quickcheck! {
    fn quickcheck(val: PathChange) -> () {
        assert_unchanged_via_json(val)
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use PathChange::{Apply, Revert};

    use crate::{
        blocks::{Chain4U, RawBlockHeader, chain4u},
        db::{
            MemoryDB,
            car::{AnyCar, ManyCar},
        },
        networks::{self, ChainConfig},
    };

    #[test]
    fn revert_to_ancestor_linear() {
        let store = ChainStore::calibnet();
        chain4u! {
            in store.blockstore();
            [_genesis = store.genesis_block_header()]
            -> [a] -> [b] -> [c, d] -> [e]
        };

        // simple
        assert_path_change(&store, b, a, [Revert(&[b])]);

        // from multi-member tipset
        assert_path_change(&store, [c, d], a, [Revert(&[c, d][..]), Revert(&[b])]);

        // to multi-member tipset
        assert_path_change(&store, e, [c, d], [Revert(e)]);

        // over multi-member tipset
        assert_path_change(&store, e, b, [Revert(&[e][..]), Revert(&[c, d])]);
    }

    /// Mirror how lotus handles passing an incomplete `TipsetKey`s.
    /// Tested on lotus `1.23.2`
    #[test]
    fn incomplete_tipsets() {
        let store = ChainStore::calibnet();
        chain4u! {
            in store.blockstore();
            [_genesis = store.genesis_block_header()]
            -> [a, b] -> [c] -> [d, _e] // this pattern 2 -> 1 -> 2 can be found at calibnet epoch 1369126
        };

        // apply to descendant with incomplete `from`
        assert_path_change(
            &store,
            a,
            c,
            [
                Revert(&[a][..]), // revert the incomplete tipset
                Apply(&[a, b]),   // apply the complete one
                Apply(&[c]),      // apply the destination
            ],
        );

        // apply to descendant with incomplete `to`
        assert_path_change(&store, c, d, [Apply(d)]);

        // revert to ancestor with incomplete `from`
        assert_path_change(&store, d, c, [Revert(d)]);

        // revert to ancestor with incomplete `to`
        assert_path_change(
            &store,
            c,
            a,
            [
                Revert(&[c][..]),
                Revert(&[a, b]), // revert the complete tipset
                Apply(&[a]),     // apply the incomplete one
            ],
        );
    }

    #[test]
    fn apply_to_descendant_linear() {
        let store = ChainStore::calibnet();
        chain4u! {
            in store.blockstore();
            [_genesis = store.genesis_block_header()]
            -> [a] -> [b] -> [c, d] -> [e]
        };

        // simple
        assert_path_change(&store, a, b, [Apply(&[b])]);

        // from multi-member tipset
        assert_path_change(&store, [c, d], e, [Apply(e)]);

        // to multi-member tipset
        assert_path_change(&store, b, [c, d], [Apply([c, d])]);

        // over multi-member tipset
        assert_path_change(&store, b, e, [Apply(&[c, d][..]), Apply(&[e])]);
    }

    #[test]
    fn cross_fork_simple() {
        let store = ChainStore::calibnet();
        chain4u! {
            in store.blockstore();
            [_genesis = store.genesis_block_header()]
            -> [a] -> [b1] -> [c1]
        };
        chain4u! {
            from [a] in store.blockstore();
            [b2] -> [c2]
        };

        // same height
        assert_path_change(&store, b1, b2, [Revert(b1), Apply(b2)]);

        // different height
        assert_path_change(&store, b1, c2, [Revert(b1), Apply(b2), Apply(c2)]);

        let _ = (a, c1);
    }

    impl ChainStore<Chain4U<ManyCar>> {
        fn _load(genesis_car: &'static [u8], genesis_cid: Cid) -> Self {
            let db = Arc::new(Chain4U::with_blockstore(
                ManyCar::new(MemoryDB::default())
                    .with_read_only(AnyCar::new(genesis_car).unwrap())
                    .unwrap(),
            ));
            let genesis_block_header = db.get_cbor(&genesis_cid).unwrap().unwrap();
            ChainStore::new(
                db,
                Arc::new(MemoryDB::default()),
                Arc::new(MemoryDB::default()),
                Arc::new(MemoryDB::default()),
                Arc::new(ChainConfig::calibnet()),
                genesis_block_header,
            )
            .unwrap()
        }
        pub fn calibnet() -> Self {
            Self::_load(
                networks::calibnet::DEFAULT_GENESIS,
                *networks::calibnet::GENESIS_CID,
            )
        }
    }

    /// Utility for writing ergonomic tests
    trait MakeTipset {
        fn make_tipset(self) -> Tipset;
    }

    impl MakeTipset for &RawBlockHeader {
        fn make_tipset(self) -> Tipset {
            Tipset::from(CachingBlockHeader::new(self.clone()))
        }
    }

    impl<const N: usize> MakeTipset for [&RawBlockHeader; N] {
        fn make_tipset(self) -> Tipset {
            self.as_slice().make_tipset()
        }
    }

    impl<const N: usize> MakeTipset for &[&RawBlockHeader; N] {
        fn make_tipset(self) -> Tipset {
            self.as_slice().make_tipset()
        }
    }

    impl MakeTipset for &[&RawBlockHeader] {
        fn make_tipset(self) -> Tipset {
            Tipset::new(self.iter().cloned().cloned()).unwrap()
        }
    }

    #[track_caller]
    fn assert_path_change<T: MakeTipset>(
        store: &ChainStore<impl Blockstore>,
        from: impl MakeTipset,
        to: impl MakeTipset,
        expected: impl IntoIterator<Item = PathChange<T>>,
    ) {
        fn print(path_change: &PathChange) {
            let it = match path_change {
                Revert(it) => {
                    print!("Revert(");
                    it
                }
                Apply(it) => {
                    print!(" Apply(");
                    it
                }
            };
            println!(
                "epoch = {}, key.cid = {})",
                it.epoch(),
                it.key().cid().unwrap()
            )
        }

        let actual =
            impl_chain_get_path(store, from.make_tipset().key(), to.make_tipset().key()).unwrap();
        let expected = expected
            .into_iter()
            .map(|change| match change {
                PathChange::Revert(it) => PathChange::Revert(Arc::new(it.make_tipset())),
                PathChange::Apply(it) => PathChange::Apply(Arc::new(it.make_tipset())),
            })
            .collect::<Vec<_>>();
        if expected != actual {
            println!("SUMMARY");
            println!("=======");
            println!("expected:");
            for it in &expected {
                print(it)
            }
            println!();
            println!("actual:");
            for it in &actual {
                print(it)
            }
            println!("=======\n")
        }
        assert_eq!(
            expected, actual,
            "expected change (left) does not match actual change (right)"
        )
    }
}