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diff --git a/doc/release-notes.md b/doc/release-notes.md
--- a/doc/release-notes.md
+++ b/doc/release-notes.md
@@ -5,3 +5,6 @@
<https://download.bitcoinabc.org/0.26.8/>
This release includes the following features and fixes:
+ - Add a new RPC `getblockfrompeer` which permits requesting a specific block from
+ a specific peer manually. The intended use is acquisition of stale chaintips
+ for fork monitoring and research purposes.
diff --git a/src/net_processing.h b/src/net_processing.h
--- a/src/net_processing.h
+++ b/src/net_processing.h
@@ -56,6 +56,18 @@
bool ignore_incoming_txs);
virtual ~PeerManager() {}
+ /**
+ * Attempt to manually fetch block from a given peer. We must already have
+ * the header.
+ *
+ * @param[in] config The global config
+ * @param[in] id The peer id
+ * @param[in] pindex The block index
+ * @returns Whether a request was successfully made
+ */
+ virtual bool FetchBlock(const Config &config, NodeId id,
+ const CBlockIndex &block_index) = 0;
+
/** Begin running background tasks, should only be called once */
virtual void StartScheduledTasks(CScheduler &scheduler) = 0;
diff --git a/src/net_processing.cpp b/src/net_processing.cpp
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -494,6 +494,8 @@
/** Implement PeerManager */
void StartScheduledTasks(CScheduler &scheduler) override;
void CheckForStaleTipAndEvictPeers() override;
+ bool FetchBlock(const Config &config, NodeId id,
+ const CBlockIndex &block_index) override;
bool GetNodeStateStats(NodeId nodeid,
CNodeStateStats &stats) const override;
bool IgnoresIncomingTxs() override { return m_ignore_incoming_txs; }
@@ -2059,6 +2061,48 @@
STALE_RELAY_AGE_LIMIT);
}
+bool PeerManagerImpl::FetchBlock(const Config &config, NodeId id,
+ const CBlockIndex &block_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;
+ }
+ // Mark block as in-flight unless it already is (for this peer).
+ // If a block was already in-flight for a different peer, its BLOCKTXN
+ // response will be dropped.
+ if (!BlockRequested(config, id, block_index)) {
+ return false;
+ }
+
+ // Construct message to request the block
+ const BlockHash &hash{block_index.GetBlockHash()};
+ std::vector<CInv> invs{CInv(MSG_BLOCK, 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,
diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
--- a/src/rpc/blockchain.cpp
+++ b/src/rpc/blockchain.cpp
@@ -19,6 +19,8 @@
#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>
@@ -875,6 +877,69 @@
};
}
+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"
+ "Subsequent calls for the same block and a new peer will cause the "
+ "response from the previous peer to be ignored.\n"
+ "\nReturns an empty JSON object if the request was successfully "
+ "scheduled.",
+ {
+ {"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", /*optional=*/true,
+ "any warnings"}}},
+ RPCExamples{HelpExampleCli("getblockfrompeer",
+ "\"00000000c937983704a73af28acdec37b049d214a"
+ "dbda81d7e2a3dd146f6ed09\" 0") +
+ HelpExampleRpc("getblockfrompeer",
+ "\"00000000c937983704a73af28acdec37b049d214a"
+ "dbda81d7e2a3dd146f6ed09\" 0")},
+ [&](const RPCHelpMan &self, const Config &config,
+ const JSONRPCRequest &request) -> UniValue {
+ const NodeContext &node = EnsureAnyNodeContext(request.context);
+ ChainstateManager &chainman = EnsureChainman(node);
+ PeerManager &peerman = EnsurePeerman(node);
+ CConnman &connman = EnsureConnman(node);
+
+ const BlockHash hash{ParseHashV(request.params[0], "hash")};
+ const NodeId 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.hasData()) {
+ result.pushKV("warnings", "Block already downloaded");
+ } else if (!peerman.FetchBlock(config, nodeid, *index)) {
+ throw JSONRPCError(RPC_MISC_ERROR,
+ "Failed to fetch block from peer");
+ }
+ return result;
+ },
+ };
+}
+
static RPCHelpMan getblockhash() {
return RPCHelpMan{
"getblockhash",
@@ -3309,6 +3374,7 @@
// ------------------ ----------------------
{ "blockchain", getbestblockhash, },
{ "blockchain", getblock, },
+ { "blockchain", getblockfrompeer, },
{ "blockchain", getblockchaininfo, },
{ "blockchain", getblockcount, },
{ "blockchain", getblockhash, },
diff --git a/src/rpc/client.cpp b/src/rpc/client.cpp
--- a/src/rpc/client.cpp
+++ b/src/rpc/client.cpp
@@ -49,6 +49,7 @@
{"getbalance", 1, "minconf"},
{"getbalance", 2, "include_watchonly"},
{"getbalance", 3, "avoid_reuse"},
+ {"getblockfrompeer", 1, "nodeid"},
{"getblockhash", 0, "height"},
{"waitforblockheight", 0, "height"},
{"waitforblockheight", 1, "timeout"},
diff --git a/src/validation.cpp b/src/validation.cpp
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -4335,6 +4335,7 @@
// 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
// If we didn't ask for it:
if (!fRequested) {
diff --git a/test/functional/rpc_getblockfrompeer.py b/test/functional/rpc_getblockfrompeer.py
new file mode 100755
--- /dev/null
+++ b/test/functional/rpc_getblockfrompeer.py
@@ -0,0 +1,91 @@
+#!/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
+ self.extra_args = [[], ["-noparkdeepreorg"]]
+
+ 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")
+ x = next(
+ filter(
+ lambda x: x['hash'] == short_tip,
+ self.nodes[0].getchaintips()))
+ assert_equal(x['status'], "headers-only")
+ 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 "warnings" not 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()

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