feat(api): implement the ChainGetFinalizedTipset API

src/rpc/methods/chain.rs

@@ -140,11 +140,62 @@ impl RpcMethod<0> for ChainGetFinalizedTipset {
     type Params = ();
     type Ok = Tipset;
 
-    async fn handle(_ctx: Ctx<impl Blockstore>, (): Self::Params) -> Result<Self::Ok, ServerError> {
-        Err(ServerError::stubbed_for_openrpc())
+    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).clone())
+            }
+            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).clone())
+            }
+        }
     }
 }
 
+// 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";

src/rpc/methods/f3.rs

@@ -698,7 +698,10 @@ impl RpcMethod<0> for F3GetLatestCertificate {
     type Params = ();
     type Ok = FinalityCertificate;
 
-    async fn handle(_: Ctx<impl Blockstore>, _: Self::Params) -> Result<Self::Ok, ServerError> {
+    async fn handle(
+        _: Ctx<impl Blockstore + Send + Sync + 'static>,
+        _: Self::Params,
+    ) -> Result<Self::Ok, ServerError> {
         let client = get_rpc_http_client()?;
         let response: LotusJson<Self::Ok> = client.request(Self::NAME, ArrayParams::new()).await?;
         Ok(response.into_inner())
@@ -948,7 +951,7 @@ pub fn get_f3_rpc_endpoint() -> Cow<'static, str> {
     }
 }
 
-fn get_rpc_http_client() -> anyhow::Result<jsonrpsee::http_client::HttpClient> {
+pub fn get_rpc_http_client() -> anyhow::Result<jsonrpsee::http_client::HttpClient> {
     let client = jsonrpsee::http_client::HttpClientBuilder::new()
         .build(format!("http://{}", get_f3_rpc_endpoint()))?;
     Ok(client)

src/tool/subcommands/api_cmd/api_compare_tests.rs

@@ -453,6 +453,7 @@ fn chain_tests_with_tipset<DB: Blockstore>(
             .clone()
             .into(),))?),
         RpcTest::identity(ChainTipSetWeight::request((tipset.key().into(),))?),
+        RpcTest::basic(ChainGetFinalizedTipset::request(())?),
     ];
 
     for block in tipset.block_headers() {

src/tool/subcommands/api_cmd/test_snapshots.txt

@@ -5,6 +5,7 @@ filecoin_chaingetevents_1746450533519970.rpcsnap.json.zst
 filecoin_chaingetevents_1746450533600537.rpcsnap.json.zst
 filecoin_chaingetevents_1746450551991052.rpcsnap.json.zst
 filecoin_chaingetevents_1750327595269729.rpcsnap.json.zst
+filecoin_chaingetfinalizedtipset_1759828121342574.rpcsnap.json.zst
 filecoin_chaingetgenesis_1736937286915866.rpcsnap.json.zst
 filecoin_chaingetmessage_1741270616352800.rpcsnap.json.zst
 filecoin_chaingetmessagesintipset_1741270616353560.rpcsnap.json.zst