Implement "getchaintips" RPC command to monitor blockchain forks.

Port over https://github.com/chronokings/huntercoin/pull/19 from
Huntercoin:  This implements a new RPC command "getchaintips" that can be
used to find all currently active chain heads.  This is similar to the
-printblocktree startup option, but it can be used without restarting
just via the RPC interface on a running daemon.

1 files changed, 70 insertions, 0 deletions

diff --git a/src/rpcblockchain.cpp b/src/rpcblockchain.cpp
index 253693e624..1e5198b85c 100644
--- a/src/rpcblockchain.cpp
+++ b/src/rpcblockchain.cpp
@@ -461,3 +461,73 @@ Value getblockchaininfo(const Array& params, bool fHelp)
     obj.push_back(Pair("chainwork",             chainActive.Tip()->nChainWork.GetHex()));
     return obj;
 }
+
+/* Comparison function for sorting the getchaintips heads.  */
+struct CompareBlocksByHeight
+{
+    bool operator()(const CBlockIndex* a, const CBlockIndex* b) const
+    {
+        /* Make sure that unequal blocks with the same height do not compare
+           equal.  Use the pointers themselves to make a distinction.  */
+
+        if (a->nHeight != b->nHeight)
+          return (a->nHeight > b->nHeight);
+
+        return a < b;
+    }
+};
+
+Value getchaintips(const Array& params, bool fHelp)
+{
+    if (fHelp || params.size() != 0)
+        throw runtime_error(
+            "getchaintips\n"
+            "Return information about all known tips in the block tree,"
+            " including the main chain as well as orphaned branches.\n"
+            "\nResult:\n"
+            "[\n"
+            "  {\n"
+            "    \"height\": xxxx,         (numeric) height of the chain tip\n"
+            "    \"hash\": \"xxxx\",         (string) block hash of the tip\n"
+            "    \"branchlen\": 0          (numeric) zero for main chain\n"
+            "  },\n"
+            "  {\n"
+            "    \"height\": xxxx,\n"
+            "    \"hash\": \"xxxx\",\n"
+            "    \"branchlen\": 1          (numeric) length of branch connecting the tip to the main chain\n"
+            "  }\n"
+            "]\n"
+            "\nExamples:\n"
+            + HelpExampleCli("getchaintips", "")
+            + HelpExampleRpc("getchaintips", "")
+        );
+
+    /* Build up a list of chain tips.  We start with the list of all
+       known blocks, and successively remove blocks that appear as pprev
+       of another block.  */
+    std::set<const CBlockIndex*, CompareBlocksByHeight> setTips;
+    BOOST_FOREACH(const PAIRTYPE(const uint256, CBlockIndex*)& item, mapBlockIndex)
+        setTips.insert(item.second);
+    BOOST_FOREACH(const PAIRTYPE(const uint256, CBlockIndex*)& item, mapBlockIndex)
+    {
+        const CBlockIndex* pprev = item.second->pprev;
+        if (pprev)
+            setTips.erase(pprev);
+    }
+
+    /* Construct the output array.  */
+    Array res;
+    BOOST_FOREACH(const CBlockIndex* block, setTips)
+    {
+        Object obj;
+        obj.push_back(Pair("height", block->nHeight));
+        obj.push_back(Pair("hash", block->phashBlock->GetHex()));
+
+        const int branchLen = block->nHeight - chainActive.FindFork(block)->nHeight;
+        obj.push_back(Pair("branchlen", branchLen));
+
+        res.push_back(obj);
+    }
+
+    return res;
+}