Add getblockheader RPC call

Alternative to getblock that works even when the block itself has been
pruned, returning all available information.

src/rpcblockchain.cpp

@@ -72,6 +72,32 @@ double GetNetworkDifficulty(const CBlockIndex* blockindex)
     return GetDifficultyINTERNAL(blockindex, true);
 }
 
+UniValue blockheaderToJSON(const CBlockIndex* blockindex)
+{
+    UniValue result(UniValue::VOBJ);
+    result.push_back(Pair("hash", blockindex->GetBlockHash().GetHex()));
+    int confirmations = -1;
+    // Only report confirmations if the block is on the main chain
+    if (chainActive.Contains(blockindex))
+        confirmations = chainActive.Height() - blockindex->nHeight + 1;
+    result.push_back(Pair("confirmations", confirmations));
+    result.push_back(Pair("height", blockindex->nHeight));
+    result.push_back(Pair("version", blockindex->nVersion));
+    result.push_back(Pair("merkleroot", blockindex->hashMerkleRoot.GetHex()));
+    result.push_back(Pair("time", (int64_t)blockindex->nTime));
+    result.push_back(Pair("nonce", (uint64_t)blockindex->nNonce));
+    result.push_back(Pair("bits", strprintf("%08x", blockindex->nBits)));
+    result.push_back(Pair("difficulty", GetDifficulty(blockindex)));
+    result.push_back(Pair("chainwork", blockindex->nChainWork.GetHex()));
+
+    if (blockindex->pprev)
+        result.push_back(Pair("previousblockhash", blockindex->pprev->GetBlockHash().GetHex()));
+    CBlockIndex *pnext = chainActive.Next(blockindex);
+    if (pnext)
+        result.push_back(Pair("nextblockhash", pnext->GetBlockHash().GetHex()));
+    return result;
+}
+
 
 UniValue blockToJSON(const CBlock& block, const CBlockIndex* blockindex, bool txDetails = false)
 {
@@ -277,6 +303,62 @@ UniValue getblockhash(const UniValue& params, bool fHelp)
     return pblockindex->GetBlockHash().GetHex();
 }
 
+UniValue getblockheader(const UniValue& params, bool fHelp)
+{
+    if (fHelp || params.size() < 1 || params.size() > 2)
+        throw runtime_error(
+            "getblockheader \"hash\" ( verbose )\n"
+            "\nIf verbose is false, returns a string that is serialized, hex-encoded data for blockheader 'hash'.\n"
+            "If verbose is true, returns an Object with information about blockheader <hash>.\n"
+            "\nArguments:\n"
+            "1. \"hash\"          (string, required) The block hash\n"
+            "2. verbose           (boolean, optional, default=true) true for a json object, false for the hex encoded data\n"
+            "\nResult (for verbose = true):\n"
+            "{\n"
+            "  \"hash\" : \"hash\",     (string) the block hash (same as provided)\n"
+            "  \"confirmations\" : n,   (numeric) The number of confirmations, or -1 if the block is not on the main chain\n"
+            "  \"height\" : n,          (numeric) The block height or index\n"
+            "  \"version\" : n,         (numeric) The block version\n"
+            "  \"merkleroot\" : \"xxxx\", (string) The merkle root\n"
+            "  \"time\" : ttt,          (numeric) The block time in seconds since epoch (Jan 1 1970 GMT)\n"
+            "  \"nonce\" : n,           (numeric) The nonce\n"
+            "  \"bits\" : \"1d00ffff\", (string) The bits\n"
+            "  \"difficulty\" : x.xxx,  (numeric) The difficulty\n"
+            "  \"previousblockhash\" : \"hash\",  (string) The hash of the previous block\n"
+            "  \"nextblockhash\" : \"hash\"       (string) The hash of the next block\n"
+            "}\n"
+            "\nResult (for verbose=false):\n"
+            "\"data\"             (string) A string that is serialized, hex-encoded data for block 'hash'.\n"
+            "\nExamples:\n"
+            + HelpExampleCli("getblockheader", "\"00000000c937983704a73af28acdec37b049d214adbda81d7e2a3dd146f6ed09\"")
+            + HelpExampleRpc("getblockheader", "\"00000000c937983704a73af28acdec37b049d214adbda81d7e2a3dd146f6ed09\"")
+        );
+
+    LOCK(cs_main);
+
+    std::string strHash = params[0].get_str();
+    uint256 hash(uint256S(strHash));
+
+    bool fVerbose = true;
+    if (params.size() > 1)
+        fVerbose = params[1].get_bool();
+
+    if (mapBlockIndex.count(hash) == 0)
+        throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Block not found");
+
+    CBlockIndex* pblockindex = mapBlockIndex[hash];
+
+    if (!fVerbose)
+    {
+        CDataStream ssBlock(SER_NETWORK, PROTOCOL_VERSION);
+        ssBlock << pblockindex->GetBlockHeader();
+        std::string strHex = HexStr(ssBlock.begin(), ssBlock.end());
+        return strHex;
+    }
+
+    return blockheaderToJSON(pblockindex);
+}
+
 UniValue getblock(const UniValue& params, bool fHelp)
 {
     if (fHelp || params.size() < 1 || params.size() > 2)

src/rpcclient.cpp

@@ -70,6 +70,7 @@ static const CRPCConvertParam vRPCConvertParams[] =
     { "listunspent", 1 },
     { "listunspent", 2 },
     { "getblock", 1 },
+    { "getblockheader", 1 },
     { "gettransaction", 1 },
     { "getrawtransaction", 1 },
     { "createrawtransaction", 0 },

src/rpcserver.cpp

@@ -296,6 +296,7 @@ static const CRPCCommand vRPCCommands[] =
     { "blockchain",         "getblockcount",          &getblockcount,          true  },
     { "blockchain",         "getblock",               &getblock,               true  },
     { "blockchain",         "getblockhash",           &getblockhash,           true  },
+    { "blockchain",         "getblockheader",         &getblockheader,         true  },
     { "blockchain",         "getchaintips",           &getchaintips,           true  },
     { "blockchain",         "getdifficulty",          &getdifficulty,          true  },
     { "blockchain",         "getmempoolinfo",         &getmempoolinfo,         true  },

src/rpcserver.h

@@ -248,6 +248,7 @@ extern UniValue settxfee(const UniValue& params, bool fHelp);
 extern UniValue getmempoolinfo(const UniValue& params, bool fHelp);
 extern UniValue getrawmempool(const UniValue& params, bool fHelp);
 extern UniValue getblockhash(const UniValue& params, bool fHelp);
+extern UniValue getblockheader(const UniValue& params, bool fHelp);
 extern UniValue getblock(const UniValue& params, bool fHelp);
 extern UniValue gettxoutsetinfo(const UniValue& params, bool fHelp);
 extern UniValue gettxout(const UniValue& params, bool fHelp);