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.

qa/rpc-tests/getchaintips.py

@@ -0,0 +1,24 @@
+#!/usr/bin/env python
+# Copyright (c) 2014 The Bitcoin Core developers
+# Distributed under the MIT/X11 software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+# Exercise the getchaintips API.
+
+# Since the test framework does not generate orphan blocks, we can
+# unfortunately not check for them!
+
+from test_framework import BitcoinTestFramework
+from util import assert_equal
+
+class GetChainTipsTest (BitcoinTestFramework):
+
+    def run_test (self, nodes):
+        res = nodes[0].getchaintips ()
+        assert_equal (len (res), 1)
+        res = res[0]
+        assert_equal (res['branchlen'], 0)
+        assert_equal (res['height'], 200)
+
+if __name__ == '__main__':
+    GetChainTipsTest ().main ()

src/main.cpp

@@ -444,7 +444,7 @@ CBlockIndex *CChain::FindFork(const CBlockLocator &locator) const {
     return Genesis();
 }
 
-CBlockIndex *CChain::FindFork(CBlockIndex *pindex) const {
+const CBlockIndex *CChain::FindFork(const CBlockIndex *pindex) const {
     if (pindex->nHeight > Height())
         pindex = pindex->GetAncestor(Height());
     while (pindex && !Contains(pindex))
@@ -2067,8 +2067,8 @@ static CBlockIndex* FindMostWorkChain() {
 static bool ActivateBestChainStep(CValidationState &state, CBlockIndex *pindexMostWork) {
     AssertLockHeld(cs_main);
     bool fInvalidFound = false;
-    CBlockIndex *pindexOldTip = chainActive.Tip();
-    CBlockIndex *pindexFork = chainActive.FindFork(pindexMostWork);
+    const CBlockIndex *pindexOldTip = chainActive.Tip();
+    const CBlockIndex *pindexFork = chainActive.FindFork(pindexMostWork);
 
     // Disconnect active blocks which are no longer in the best chain.
     while (chainActive.Tip() && chainActive.Tip() != pindexFork) {

src/main.h

@@ -1068,7 +1068,7 @@ public:
     CBlockIndex *FindFork(const CBlockLocator &locator) const;
 
     /** Find the last common block between this chain and a block index entry. */
-    CBlockIndex *FindFork(CBlockIndex *pindex) const;
+    const CBlockIndex *FindFork(const CBlockIndex *pindex) const;
 };
 
 /** The currently-connected chain of blocks. */

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;
+}

src/rpcserver.cpp

@@ -235,6 +235,7 @@ static const CRPCCommand vRPCCommands[] =
     { "getblockcount",          &getblockcount,          true,      false,      false },
     { "getblock",               &getblock,               true,      false,      false },
     { "getblockhash",           &getblockhash,           true,      false,      false },
+    { "getchaintips",           &getchaintips,           true,      false,      false },
     { "getdifficulty",          &getdifficulty,          true,      false,      false },
     { "getrawmempool",          &getrawmempool,          true,      false,      false },
     { "gettxout",               &gettxout,               true,      false,      false },

src/rpcserver.h

@@ -205,5 +205,6 @@ extern json_spirit::Value getblock(const json_spirit::Array& params, bool fHelp)
 extern json_spirit::Value gettxoutsetinfo(const json_spirit::Array& params, bool fHelp);
 extern json_spirit::Value gettxout(const json_spirit::Array& params, bool fHelp);
 extern json_spirit::Value verifychain(const json_spirit::Array& params, bool fHelp);
+extern json_spirit::Value getchaintips(const json_spirit::Array& params, bool fHelp);
 
 #endif