add waitfornewblock/waitforblock/waitforblockheight rpcs and use them for tests

waitfornewblock waits until a new block is received, or the timeout expires, then
returns the current block height/hash.

waitforblock waits for a specific blockhash, or until the timeout expires, then
returns the current block height/hash. If the target blockhash is the current
tip, it will return immediately.

waitforblockheight waits until the tip has reached a certain height or higher,
then returns the current height and hash.

waitforblockheight is used to avoid polling in the rpc tests.

qa/rpc-tests/test_framework/util.py

@@ -125,12 +125,16 @@ def sync_blocks(rpc_connections, wait=1, timeout=60):
     """
     Wait until everybody has the same tip
     """
+    maxheight = 0
     while timeout > 0:
-        tips = [ x.getbestblockhash() for x in rpc_connections ]
+        tips = [ x.waitforblockheight(maxheight, int(wait * 1000)) for x in rpc_connections ]
+        heights = [ x["height"] for x in tips ]
         if tips == [ tips[0] ]*len(tips):
             return True
-        time.sleep(wait)
+        if heights == [ heights[0] ]*len(heights): #heights are the same but hashes are not
+            raise AssertionError("Block sync failed")
         timeout -= wait
+        maxheight = max(heights)
     raise AssertionError("Block sync failed")
 
 def sync_mempools(rpc_connections, wait=1, timeout=60):

src/init.cpp

@@ -280,9 +280,15 @@ bool static Bind(const CService &addr, unsigned int flags) {
     }
     return true;
 }
+void OnRPCStarted()
+{
+    uiInterface.NotifyBlockTip.connect(&RPCNotifyBlockChange);
+}
 
 void OnRPCStopped()
 {
+    uiInterface.NotifyBlockTip.disconnect(&RPCNotifyBlockChange);
+    RPCNotifyBlockChange(false, nullptr);
     cvBlockChange.notify_all();
     LogPrint("rpc", "RPC stopped.\n");
 }
@@ -666,6 +672,7 @@ bool InitSanityCheck(void)
 
 bool AppInitServers(boost::thread_group& threadGroup)
 {
+    RPCServer::OnStarted(&OnRPCStarted);
     RPCServer::OnStopped(&OnRPCStopped);
     RPCServer::OnPreCommand(&OnRPCPreCommand);
     if (!InitHTTPServer())
@@ -1357,6 +1364,7 @@ bool AppInit2(boost::thread_group& threadGroup, CScheduler& scheduler)
                 {
                     LOCK(cs_main);
                     CBlockIndex* tip = chainActive.Tip();
+                    RPCNotifyBlockChange(true, tip);
                     if (tip && tip->nTime > GetAdjustedTime() + 2 * 60 * 60) {
                         strLoadError = _("The block database contains a block which appears to be from the future. "
                                 "This may be due to your computer's date and time being set incorrectly. "

src/rpc/blockchain.cpp

@@ -26,8 +26,20 @@
 
 #include <boost/thread/thread.hpp> // boost::thread::interrupt
 
+#include <mutex>
+#include <condition_variable>
 using namespace std;
 
+struct CUpdatedBlock
+{
+    uint256 hash;
+    int height;
+};
+
+static std::mutex cs_blockchange;
+static std::condition_variable cond_blockchange;
+static CUpdatedBlock latestblock;
+
 extern void TxToJSON(const CTransaction& tx, const uint256 hashBlock, UniValue& entry);
 void ScriptPubKeyToJSON(const CScript& scriptPubKey, UniValue& out, bool fIncludeHex);
 
@@ -168,6 +180,138 @@ UniValue getbestblockhash(const UniValue& params, bool fHelp)
     return chainActive.Tip()->GetBlockHash().GetHex();
 }
 
+void RPCNotifyBlockChange(bool ibd, const CBlockIndex * pindex)
+{
+    if(pindex) {
+        std::lock_guard<std::mutex> lock(cs_blockchange);
+        latestblock.hash = pindex->GetBlockHash();
+        latestblock.height = pindex->nHeight;
+    }
+	cond_blockchange.notify_all();
+}
+
+UniValue waitfornewblock(const UniValue& params, bool fHelp)
+{
+    if (fHelp || params.size() > 1)
+        throw runtime_error(
+            "waitfornewblock\n"
+            "\nWaits for a specific new block and returns useful info about it.\n"
+            "\nReturns the current block on timeout or exit.\n"
+            "\nArguments:\n"
+            "1. timeout (milliseconds) (int, optional, default=false)\n"
+            "\nResult::\n"
+            "{                           (json object)\n"
+            "  \"hash\" : {       (string) The blockhash\n"
+            "  \"height\" : {     (int) Block height\n"
+            "}\n"
+            "\nExamples\n"
+            + HelpExampleCli("waitfornewblock", "1000")
+            + HelpExampleRpc("waitfornewblock", "1000")
+        );
+    int timeout = 0;
+    if (params.size() > 0)
+        timeout = params[0].get_int();
+
+    CUpdatedBlock block;
+    {
+        std::unique_lock<std::mutex> lock(cs_blockchange);
+        block = latestblock;
+        if(timeout)
+            cond_blockchange.wait_for(lock, std::chrono::milliseconds(timeout), [&block]{return latestblock.height != block.height || latestblock.hash != block.hash || !IsRPCRunning(); });
+        else
+            cond_blockchange.wait(lock, [&block]{return latestblock.height != block.height || latestblock.hash != block.hash || !IsRPCRunning(); });
+        block = latestblock;
+    }
+    UniValue ret(UniValue::VOBJ);
+    ret.push_back(Pair("hash", block.hash.GetHex()));
+    ret.push_back(Pair("height", block.height));
+    return ret;
+}
+
+UniValue waitforblock(const UniValue& params, bool fHelp)
+{
+    if (fHelp || params.size() < 1 || params.size() > 2)
+        throw runtime_error(
+            "waitforblock\n"
+            "\nWaits for a specific new block and returns useful info about it.\n"
+            "\nReturns the current block on timeout or exit.\n"
+            "\nArguments:\n"
+            "1. blockhash to wait for (string)\n"
+            "2. timeout (milliseconds) (int, optional, default=false)\n"
+            "\nResult::\n"
+            "{                           (json object)\n"
+            "  \"hash\" : {       (string) The blockhash\n"
+            "  \"height\" : {     (int) Block height\n"
+            "}\n"
+            "\nExamples\n"
+            + HelpExampleCli("waitforblock", "\"0000000000079f8ef3d2c688c244eb7a4570b24c9ed7b4a8c619eb02596f8862\", 1000")
+            + HelpExampleRpc("waitforblock", "\"0000000000079f8ef3d2c688c244eb7a4570b24c9ed7b4a8c619eb02596f8862\", 1000")
+        );
+    int timeout = 0;
+
+    uint256 hash = uint256S(params[0].get_str());
+
+    if (params.size() > 1)
+        timeout = params[1].get_int();
+
+    CUpdatedBlock block;
+    {
+        std::unique_lock<std::mutex> lock(cs_blockchange);
+        if(timeout)
+            cond_blockchange.wait_for(lock, std::chrono::milliseconds(timeout), [&hash]{return latestblock.hash == hash || !IsRPCRunning();});
+        else
+            cond_blockchange.wait(lock, [&hash]{return latestblock.hash == hash || !IsRPCRunning(); });
+        block = latestblock;
+    }
+
+    UniValue ret(UniValue::VOBJ);
+    ret.push_back(Pair("hash", block.hash.GetHex()));
+    ret.push_back(Pair("height", block.height));
+    return ret;
+}
+
+UniValue waitforblockheight(const UniValue& params, bool fHelp)
+{
+    if (fHelp || params.size() < 1 || params.size() > 2)
+        throw runtime_error(
+            "waitforblock\n"
+            "\nWaits for (at least) block height and returns the height and hash\n"
+            "\nof the current tip.\n"
+            "\nReturns the current block on timeout or exit.\n"
+            "\nArguments:\n"
+            "1. block height to wait for (int)\n"
+            "2. timeout (milliseconds) (int, optional, default=false)\n"
+            "\nResult::\n"
+            "{                           (json object)\n"
+            "  \"hash\" : {       (string) The blockhash\n"
+            "  \"height\" : {     (int) Block height\n"
+            "}\n"
+            "\nExamples\n"
+            + HelpExampleCli("waitforblockheight", "\"100\", 1000")
+            + HelpExampleRpc("waitforblockheight", "\"100\", 1000")
+        );
+    int timeout = 0;
+
+    int height = params[0].get_int();
+
+    if (params.size() > 1)
+        timeout = params[1].get_int();
+
+    CUpdatedBlock block;
+    {
+        std::unique_lock<std::mutex> lock(cs_blockchange);
+        if(timeout)
+            cond_blockchange.wait_for(lock, std::chrono::milliseconds(timeout), [&height]{return latestblock.height >= height || !IsRPCRunning();});
+        else
+            cond_blockchange.wait(lock, [&height]{return latestblock.height >= height || !IsRPCRunning(); });
+        block = latestblock;
+    }
+    UniValue ret(UniValue::VOBJ);
+    ret.push_back(Pair("hash", block.hash.GetHex()));
+    ret.push_back(Pair("height", block.height));
+    return ret;
+}
+
 UniValue getdifficulty(const UniValue& params, bool fHelp)
 {
     if (fHelp || params.size() != 0)
@@ -1203,6 +1347,9 @@ static const CRPCCommand commands[] =
     /* Not shown in help */
     { "hidden",             "invalidateblock",        &invalidateblock,        true  },
     { "hidden",             "reconsiderblock",        &reconsiderblock,        true  },
+    { "hidden",             "waitfornewblock",        &waitfornewblock,        true  },
+    { "hidden",             "waitforblock",           &waitforblock,           true  },
+    { "hidden",             "waitforblockheight",     &waitforblockheight,     true  },
 };
 
 void RegisterBlockchainRPCCommands(CRPCTable &t)

src/rpc/client.cpp

@@ -46,6 +46,12 @@ static const CRPCConvertParam vRPCConvertParams[] =
     { "getbalance", 1 },
     { "getbalance", 2 },
     { "getblockhash", 0 },
+    { "waitforblockheight", 0 },
+    { "waitforblockheight", 1 },
+    { "waitforblock", 1 },
+    { "waitforblock", 2 },
+    { "waitfornewblock", 0 },
+    { "waitfornewblock", 1 },
     { "move", 2 },
     { "move", 3 },
     { "sendfrom", 2 },

src/rpc/server.h

@@ -194,5 +194,6 @@ bool StartRPC();
 void InterruptRPC();
 void StopRPC();
 std::string JSONRPCExecBatch(const UniValue& vReq);
+void RPCNotifyBlockChange(bool ibd, const CBlockIndex *);
 
 #endif // BITCOIN_RPCSERVER_H