rpc: getblockfrompeer

Co-authored-by: John Newbery <john@johnnewbery.com>

src/net_processing.cpp

@@ -312,6 +312,7 @@ public:
     /** Implement PeerManager */
     void StartScheduledTasks(CScheduler& scheduler) override;
     void CheckForStaleTipAndEvictPeers() override;
+    bool FetchBlock(NodeId id, const uint256& hash, const CBlockIndex& index) override;
     bool GetNodeStateStats(NodeId nodeid, CNodeStateStats& stats) const override;
     bool IgnoresIncomingTxs() override { return m_ignore_incoming_txs; }
     void SendPings() override;
@@ -1427,6 +1428,41 @@ bool PeerManagerImpl::BlockRequestAllowed(const CBlockIndex* pindex)
            (GetBlockProofEquivalentTime(*pindexBestHeader, *pindex, *pindexBestHeader, m_chainparams.GetConsensus()) < STALE_RELAY_AGE_LIMIT);
 }
 
+bool PeerManagerImpl::FetchBlock(NodeId id, const uint256& hash, const CBlockIndex& index)
+{
+    if (fImporting || fReindex) return false;
+
+    LOCK(cs_main);
+    // Ensure this peer exists and hasn't been disconnected
+    CNodeState* state = State(id);
+    if (state == nullptr) return false;
+    // Ignore pre-segwit peers
+    if (!state->fHaveWitness) return false;
+
+    // Mark block as in-flight unless it already is
+    if (!BlockRequested(id, index)) return false;
+
+    // Construct message to request the block
+    std::vector<CInv> invs{CInv(MSG_BLOCK | MSG_WITNESS_FLAG, hash)};
+
+    // Send block request message to the peer
+    bool success = m_connman.ForNode(id, [this, &invs](CNode* node) {
+        const CNetMsgMaker msgMaker(node->GetCommonVersion());
+        this->m_connman.PushMessage(node, msgMaker.Make(NetMsgType::GETDATA, invs));
+        return true;
+    });
+
+    if (success) {
+        LogPrint(BCLog::NET, "Requesting block %s from peer=%d\n",
+                 hash.ToString(), id);
+    } else {
+        RemoveBlockRequest(hash);
+        LogPrint(BCLog::NET, "Failed to request block %s from peer=%d\n",
+                 hash.ToString(), id);
+    }
+    return success;
+}
+
 std::unique_ptr<PeerManager> PeerManager::make(const CChainParams& chainparams, CConnman& connman, AddrMan& addrman,
                                                BanMan* banman, ChainstateManager& chainman,
                                                CTxMemPool& pool, bool ignore_incoming_txs)

src/net_processing.h

@@ -42,6 +42,16 @@ public:
                                              CTxMemPool& pool, bool ignore_incoming_txs);
     virtual ~PeerManager() { }
 
+    /**
+     * Attempt to manually fetch block from a given peer. We must already have the header.
+     *
+     * @param[in]  id       The peer id
+     * @param[in]  hash     The block hash
+     * @param[in]  pindex   The blockindex
+     * @returns             Whether a request was successfully made
+     */
+    virtual bool FetchBlock(NodeId id, const uint256& hash, const CBlockIndex& pindex) = 0;
+
     /** Begin running background tasks, should only be called once */
     virtual void StartScheduledTasks(CScheduler& scheduler) = 0;
 

src/rpc/blockchain.cpp

@@ -18,6 +18,8 @@
 #include <hash.h>
 #include <index/blockfilterindex.h>
 #include <index/coinstatsindex.h>
+#include <net.h>
+#include <net_processing.h>
 #include <node/blockstorage.h>
 #include <node/coinstats.h>
 #include <node/context.h>
@@ -755,6 +757,58 @@ static RPCHelpMan getmempoolentry()
     };
 }
 
+static RPCHelpMan getblockfrompeer()
+{
+    return RPCHelpMan{"getblockfrompeer",
+                "\nAttempt to fetch block from a given peer.\n"
+                "\nWe must have the header for this block, e.g. using submitheader.\n"
+                "\nReturns {} if a block-request was successfully scheduled\n",
+                {
+                    {"blockhash", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The block hash"},
+                    {"nodeid", RPCArg::Type::NUM, RPCArg::Optional::NO, "The node ID (see getpeerinfo for node IDs)"},
+                },
+                RPCResult{RPCResult::Type::OBJ, "", "",
+                {
+                    {RPCResult::Type::STR, "warnings", "any warnings"}
+                }},
+                RPCExamples{
+                    HelpExampleCli("getblockfrompeer", "\"00000000c937983704a73af28acdec37b049d214adbda81d7e2a3dd146f6ed09\" 0")
+                + HelpExampleRpc("getblockfrompeer", "\"00000000c937983704a73af28acdec37b049d214adbda81d7e2a3dd146f6ed09\" 0")
+                },
+        [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
+{
+    const NodeContext& node = EnsureAnyNodeContext(request.context);
+    ChainstateManager& chainman = EnsureChainman(node);
+    PeerManager& peerman = EnsurePeerman(node);
+    CConnman& connman = EnsureConnman(node);
+
+    uint256 hash(ParseHashV(request.params[0], "hash"));
+
+    const NodeId nodeid = static_cast<NodeId>(request.params[1].get_int64());
+
+    // Check that the peer with nodeid exists
+    if (!connman.ForNode(nodeid, [](CNode* node) {return true;})) {
+        throw JSONRPCError(RPC_MISC_ERROR, strprintf("Peer nodeid %d does not exist", nodeid));
+    }
+
+    const CBlockIndex* const index = WITH_LOCK(cs_main, return chainman.m_blockman.LookupBlockIndex(hash););
+
+    if (!index) {
+        throw JSONRPCError(RPC_MISC_ERROR, "Block header missing");
+    }
+
+    UniValue result = UniValue::VOBJ;
+
+    if (index->nStatus & BLOCK_HAVE_DATA) {
+        result.pushKV("warnings", "Block already downloaded");
+    } else if (!peerman.FetchBlock(nodeid, hash, *index)) {
+        throw JSONRPCError(RPC_MISC_ERROR, "Failed to fetch block from peer");
+    }
+    return result;
+},
+    };
+}
+
 static RPCHelpMan getblockhash()
 {
     return RPCHelpMan{"getblockhash",
@@ -2612,6 +2666,7 @@ static const CRPCCommand commands[] =
     { "blockchain",         &getbestblockhash,                   },
     { "blockchain",         &getblockcount,                      },
     { "blockchain",         &getblock,                           },
+    { "blockchain",         &getblockfrompeer,                   },
     { "blockchain",         &getblockhash,                       },
     { "blockchain",         &getblockheader,                     },
     { "blockchain",         &getchaintips,                       },

src/rpc/client.cpp

@@ -56,6 +56,7 @@ static const CRPCConvertParam vRPCConvertParams[] =
     { "getbalance", 1, "minconf" },
     { "getbalance", 2, "include_watchonly" },
     { "getbalance", 3, "avoid_reuse" },
+    { "getblockfrompeer", 1, "nodeid" },
     { "getblockhash", 0, "height" },
     { "waitforblockheight", 0, "height" },
     { "waitforblockheight", 1, "timeout" },

src/test/fuzz/rpc.cpp

@@ -110,6 +110,7 @@ const std::vector<std::string> RPC_COMMANDS_SAFE_FOR_FUZZING{
     "getblockfilter",
     "getblockhash",
     "getblockheader",
+    "getblockfrompeer", // when no peers are connected, no p2p message is sent
     "getblockstats",
     "getblocktemplate",
     "getchaintips",

src/validation.cpp

@@ -3408,6 +3408,7 @@ bool CChainState::AcceptBlock(const std::shared_ptr<const CBlock>& pblock, Block
     // This requires some new chain data structure to efficiently look up if a
     // block is in a chain leading to a candidate for best tip, despite not
     // being such a candidate itself.
+    // Note that this would break the getblockfrompeer RPC
 
     // TODO: deal better with return value and error conditions for duplicate
     // and unrequested blocks.

test/functional/rpc_getblockfrompeer.py

@@ -0,0 +1,76 @@
+#!/usr/bin/env python3
+# Copyright (c) 2020 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+"""Test the getblockfrompeer RPC."""
+
+from test_framework.authproxy import JSONRPCException
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import (
+    assert_equal,
+    assert_raises_rpc_error,
+)
+
+class GetBlockFromPeerTest(BitcoinTestFramework):
+    def set_test_params(self):
+        self.num_nodes = 2
+
+    def setup_network(self):
+        self.setup_nodes()
+
+    def check_for_block(self, hash):
+        try:
+            self.nodes[0].getblock(hash)
+            return True
+        except JSONRPCException:
+            return False
+
+    def run_test(self):
+        self.log.info("Mine 4 blocks on Node 0")
+        self.generate(self.nodes[0], 4, sync_fun=self.no_op)
+        assert_equal(self.nodes[0].getblockcount(), 204)
+
+        self.log.info("Mine competing 3 blocks on Node 1")
+        self.generate(self.nodes[1], 3, sync_fun=self.no_op)
+        assert_equal(self.nodes[1].getblockcount(), 203)
+        short_tip = self.nodes[1].getbestblockhash()
+
+        self.log.info("Connect nodes to sync headers")
+        self.connect_nodes(0, 1)
+        self.sync_blocks()
+
+        self.log.info("Node 0 should only have the header for node 1's block 3")
+        for x in self.nodes[0].getchaintips():
+            if x['hash'] == short_tip:
+                assert_equal(x['status'], "headers-only")
+                break
+        else:
+            raise AssertionError("short tip not synced")
+        assert_raises_rpc_error(-1, "Block not found on disk", self.nodes[0].getblock, short_tip)
+
+        self.log.info("Fetch block from node 1")
+        peers = self.nodes[0].getpeerinfo()
+        assert_equal(len(peers), 1)
+        peer_0_peer_1_id = peers[0]["id"]
+
+        self.log.info("Arguments must be sensible")
+        assert_raises_rpc_error(-8, "hash must be of length 64 (not 4, for '1234')", self.nodes[0].getblockfrompeer, "1234", 0)
+
+        self.log.info("We must already have the header")
+        assert_raises_rpc_error(-1, "Block header missing", self.nodes[0].getblockfrompeer, "00" * 32, 0)
+
+        self.log.info("Non-existent peer generates error")
+        assert_raises_rpc_error(-1, f"Peer nodeid {peer_0_peer_1_id + 1} does not exist", self.nodes[0].getblockfrompeer, short_tip, peer_0_peer_1_id + 1)
+
+        self.log.info("Successful fetch")
+        result = self.nodes[0].getblockfrompeer(short_tip, peer_0_peer_1_id)
+        self.wait_until(lambda: self.check_for_block(short_tip), timeout=1)
+        assert(not "warnings" in result)
+
+        self.log.info("Don't fetch blocks we already have")
+        result = self.nodes[0].getblockfrompeer(short_tip, peer_0_peer_1_id)
+        assert("warnings" in result)
+        assert_equal(result["warnings"], "Block already downloaded")
+
+if __name__ == '__main__':
+    GetBlockFromPeerTest().main()

test/functional/test_runner.py

@@ -215,6 +215,7 @@ BASE_SCRIPTS = [
     'wallet_txn_clone.py --mineblock',
     'feature_notifications.py',
     'rpc_getblockfilter.py',
+    'rpc_getblockfrompeer.py',
     'rpc_invalidateblock.py',
     'feature_utxo_set_hash.py',
     'feature_rbf.py --legacy-wallet',