From 238b2af83b4711c998bbf09bc6a19a1726f23431 Mon Sep 17 00:00:00 2001
From: Juhyung Park <jh@kodebox.io>
Date: Mon, 17 Jun 2019 17:22:46 +0900
Subject: [PATCH 1/2] Add the spec of chain_getMetadataSeq

---
 spec/JSON-RPC.md | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/spec/JSON-RPC.md b/spec/JSON-RPC.md
index dd73077c4d..7fffa017d1 100644
--- a/spec/JSON-RPC.md
+++ b/spec/JSON-RPC.md
@@ -1467,6 +1467,35 @@ Errors: `Invalid Params`
 
 [Back to **List of methods**](#list-of-methods)
 
+# chain_getMetadataSeq
+Gets the sequence of metadata.
+It returns null if the block number parameter is larger than the current best block.
+
+### Params
+ 1. block number - `number` | `null`
+
+### Returns
+`number` | `null`
+
+### Request Example
+```
+  curl \
+    -H 'Content-Type: application/json' \
+    -d '{"jsonrpc": "2.0", "method": "chain_getMeatadataSeq", "params": [53], "id": 7}' \
+    localhost:8080
+```
+
+### Response Example
+```
+{
+  "jsonrpc":"2.0",
+  "result":43,
+  "id":7
+}
+```
+
+[Back to **List of methods**](#list-of-methods)
+
 ## chain_executeTransaction
 Executes the transactions and returns whether the execution is successful.
 

From 175bc6c84e254f00780c454307e42aac8bb3f99f Mon Sep 17 00:00:00 2001
From: Juhyung Park <jh@kodebox.io>
Date: Mon, 17 Jun 2019 17:45:28 +0900
Subject: [PATCH 2/2] Add `chain_getMetadataSeq` RPC

---
 core/src/client/client.rs      | 10 ++++++++++
 core/src/client/mod.rs         |  1 +
 core/src/client/test_client.rs |  4 ++++
 rpc/src/v1/impls/chain.rs      |  5 +++++
 rpc/src/v1/traits/chain.rs     |  4 ++++
 5 files changed, 24 insertions(+)

diff --git a/core/src/client/client.rs b/core/src/client/client.rs
index 8aa8507662..a5016c5bfe 100644
--- a/core/src/client/client.rs
+++ b/core/src/client/client.rs
@@ -505,6 +505,16 @@ impl EngineInfo for Client {
         })
     }
 
+    fn metadata_seq(&self, block_id: BlockId) -> Option<u64> {
+        self.state_info(block_id.into()).map(|state| {
+            state
+                .metadata()
+                .unwrap_or_else(|err| unreachable!("Unexpected failure. Maybe DB was corrupted: {:?}", err))
+                .unwrap()
+                .seq()
+        })
+    }
+
     fn block_reward(&self, block_number: u64) -> u64 {
         self.engine().block_reward(block_number)
     }
diff --git a/core/src/client/mod.rs b/core/src/client/mod.rs
index 480d555aa8..66877e16df 100644
--- a/core/src/client/mod.rs
+++ b/core/src/client/mod.rs
@@ -88,6 +88,7 @@ pub trait BlockChainTrait {
 
 pub trait EngineInfo: Send + Sync {
     fn common_params(&self, block_id: BlockId) -> Option<CommonParams>;
+    fn metadata_seq(&self, block_id: BlockId) -> Option<u64>;
     fn block_reward(&self, block_number: u64) -> u64;
     fn mining_reward(&self, block_number: u64) -> Option<u64>;
     fn recommended_confirmation(&self) -> u32;
diff --git a/core/src/client/test_client.rs b/core/src/client/test_client.rs
index 18dfa2c7ac..9fd640b1b9 100644
--- a/core/src/client/test_client.rs
+++ b/core/src/client/test_client.rs
@@ -589,6 +589,10 @@ impl EngineInfo for TestBlockChainClient {
         unimplemented!()
     }
 
+    fn metadata_seq(&self, _block_id: BlockId) -> Option<u64> {
+        unimplemented!()
+    }
+
     fn block_reward(&self, _block_number: u64) -> u64 {
         unimplemented!()
     }
diff --git a/rpc/src/v1/impls/chain.rs b/rpc/src/v1/impls/chain.rs
index 0a870eeb22..a1b6db2645 100644
--- a/rpc/src/v1/impls/chain.rs
+++ b/rpc/src/v1/impls/chain.rs
@@ -316,6 +316,11 @@ where
         }
     }
 
+    fn get_metadata_seq(&self, block_number: Option<u64>) -> Result<Option<u64>> {
+        let block_id = block_number.map(BlockId::Number).unwrap_or(BlockId::Latest);
+        Ok(self.client.metadata_seq(block_id))
+    }
+
     fn get_possible_authors(&self, block_number: Option<u64>) -> Result<Option<Vec<PlatformAddress>>> {
         Ok(self.client.possible_authors(block_number).map_err(errors::core)?)
     }
diff --git a/rpc/src/v1/traits/chain.rs b/rpc/src/v1/traits/chain.rs
index 8c6f357260..db4a0620b4 100644
--- a/rpc/src/v1/traits/chain.rs
+++ b/rpc/src/v1/traits/chain.rs
@@ -145,6 +145,10 @@ build_rpc_trait! {
         #[rpc(name = "chain_getTermMetadata")]
         fn get_term_metadata(&self, Option<u64>) -> Result<Option<(u64, u64)>>;
 
+        /// Return the current metadata seq at given block number
+        #[rpc(name = "chain_getMetadataSeq")]
+        fn get_metadata_seq(&self, Option<u64>) -> Result<Option<u64>>;
+
         /// Return the valid block authors
         #[rpc(name = "chain_getPossibleAuthors")]
         fn get_possible_authors(&self, Option<u64>) -> Result<Option<Vec<PlatformAddress>>>;