Introduce getbestchainlock rpc and fix llmq-is-cl-conflicts.py (#3094)

* Introduce getbestchainlock rpc and fix llmq-is-cl-conflicts.py

* Add `known_block` field and move `getbestchainlock` to `blockchain` rpc category

* Add CChainLockSig::IsNull() and throw an exception in getbestchainlock if there is no known chainlock yet

* drop blockHash initializer

src/llmq/quorums_chainlocks.cpp

@@ -23,6 +23,11 @@ static const std::string CLSIG_REQUESTID_PREFIX = "clsig";
 
 CChainLocksHandler* chainLocksHandler;
 
+bool CChainLockSig::IsNull() const
+{
+    return nHeight == -1 && blockHash == uint256();
+}
+
 std::string CChainLockSig::ToString() const
 {
     return strprintf("CChainLockSig(nHeight=%d, blockHash=%s)", nHeight, blockHash.ToString());
@@ -72,6 +77,12 @@ bool CChainLocksHandler::GetChainLockByHash(const uint256& hash, llmq::CChainLoc
     return true;
 }
 
+CChainLockSig CChainLocksHandler::GetBestChainLock()
+{
+    LOCK(cs);
+    return bestChainLock;
+}
+
 void CChainLocksHandler::ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStream& vRecv, CConnman& connman)
 {
     if (!sporkManager.IsSporkActive(SPORK_19_CHAINLOCKS_ENABLED)) {
@@ -101,7 +112,7 @@ void CChainLocksHandler::ProcessNewChainLock(NodeId from, const llmq::CChainLock
             return;
         }
 
-        if (bestChainLock.nHeight != -1 && clsig.nHeight <= bestChainLock.nHeight) {
+        if (!bestChainLock.IsNull() && clsig.nHeight <= bestChainLock.nHeight) {
             // no need to process/relay older CLSIGs
             return;
         }

src/llmq/quorums_chainlocks.h

@@ -38,6 +38,7 @@ public:
         READWRITE(sig);
     }
 
+    bool IsNull() const;
     std::string ToString() const;
 };
 
@@ -85,6 +86,7 @@ public:
 
     bool AlreadyHave(const CInv& inv);
     bool GetChainLockByHash(const uint256& hash, CChainLockSig& ret);
+    CChainLockSig GetBestChainLock();
 
     void ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStream& vRecv, CConnman& connman);
     void ProcessNewChainLock(NodeId from, const CChainLockSig& clsig, const uint256& hash);

src/rpc/blockchain.cpp

@@ -207,6 +207,34 @@ UniValue getbestblockhash(const JSONRPCRequest& request)
     return chainActive.Tip()->GetBlockHash().GetHex();
 }
 
+UniValue getbestchainlock(const JSONRPCRequest& request)
+{
+    if (request.fHelp || request.params.size() != 0)
+        throw std::runtime_error(
+            "getbestchainlock\n"
+            "\nReturns the block hash of the best chainlock. Throws an error if there is no known chainlock yet.\n"
+            "\nResult:\n"
+            "{\n"
+            "  \"blockhash\" : \"hash\",      (string) The block hash hex encoded\n"
+            "  \"height\" : n,              (numeric) The block height or index\n"
+            "  \"known_block\" : true|false (boolean) True if the block is known by our node\n"
+            "}\n"
+            "\nExamples:\n"
+            + HelpExampleCli("getbestchainlock", "")
+            + HelpExampleRpc("getbestchainlock", "")
+        );
+    UniValue result(UniValue::VOBJ);
+    llmq::CChainLockSig clsig = llmq::chainLocksHandler->GetBestChainLock();
+    if (clsig.IsNull()) {
+        throw JSONRPCError(RPC_INTERNAL_ERROR, "Unable to find any chainlock");
+    }
+    result.push_back(Pair("blockhash", clsig.blockHash.GetHex()));
+    result.push_back(Pair("height", clsig.nHeight));
+    LOCK(cs_main);
+    result.push_back(Pair("known_block", mapBlockIndex.count(clsig.blockHash) > 0));
+    return result;
+}
+
 void RPCNotifyBlockChange(bool ibd, const CBlockIndex * pindex)
 {
     if(pindex) {
@@ -2161,6 +2189,7 @@ static const CRPCCommand commands[] =
     { "blockchain",         "getchaintxstats",        &getchaintxstats,        true,  {"nblocks", "blockhash"} },
     { "blockchain",         "getblockstats",          &getblockstats,          true,  {"hash_or_height", "stats"} },
     { "blockchain",         "getbestblockhash",       &getbestblockhash,       true,  {} },
+    { "blockchain",         "getbestchainlock",       &getbestchainlock,       true,  {} },
     { "blockchain",         "getblockcount",          &getblockcount,          true,  {} },
     { "blockchain",         "getblock",               &getblock,               true,  {"blockhash","verbosity|verbose"} },
     { "blockchain",         "getblockhashes",         &getblockhashes,         true,  {"high","low"} },

test/functional/llmq-is-cl-conflicts.py

@@ -112,9 +112,7 @@ class LLMQ_IS_CL_Conflicts(DashTestFramework):
         cl = self.create_chainlock(self.nodes[0].getblockcount() + 1, block.sha256)
         self.test_node.send_clsig(cl)
 
-        # Give the CLSIG some time to propagate. We unfortunately can't check propagation here as "getblock/getblockheader"
-        # is required to check for CLSIGs, but this requires the block header to be propagated already
-        time.sleep(1)
+        self.wait_for_best_chainlock(self.nodes[1], "%064x" % block.sha256)
 
         # The block should get accepted now, and at the same time prune the conflicting ISLOCKs
         submit_result = self.nodes[1].submitblock(ToHex(block))
@@ -223,6 +221,17 @@ class LLMQ_IS_CL_Conflicts(DashTestFramework):
             time.sleep(0.1)
         raise AssertionError("wait_for_chainlock timed out")
 
+    def wait_for_best_chainlock(self, node, block_hash):
+        t = time.time()
+        while time.time() - t < 15:
+            try:
+                if node.getbestchainlock()["blockhash"] == block_hash:
+                    return
+            except:
+                pass
+            time.sleep(0.1)
+        raise AssertionError("wait_for_best_chainlock timed out")
+
     def create_block(self, node, vtx=[]):
         bt = node.getblocktemplate()
         height = bt['height']