Merge bitcoin/bitcoin#20295: rpc: getblockfrompeer

dce8c4c38111556ca480aa0e63c46b71f66b508f rpc: getblockfrompeer (Sjors Provoost)
b884ababc29ce963826d8a4327ed6a5e629ff175 rpc: move Ensure* helpers to server_util.h (Sjors Provoost)

Pull request description:

  This adds an RPC method to fetch a block directly from a peer. This can used to fetch stale blocks with lower proof of work that are normally ignored by the node (`headers-only` in `getchaintips`).

  Usage:
  ```
  bitcoin-cli getblockfrompeer HASH peer_n
  ```

  Closes #20155

  Limitations:
  * you have to specify which peer to fetch the block from
  * the node must already have the header

ACKs for top commit:
  jnewbery:
    ACK dce8c4c38111556ca480aa0e63c46b71f66b508f
  fjahr:
     re-ACK dce8c4c38111556ca480aa0e63c46b71f66b508f

Tree-SHA512: 843ba2b7a308f640770d624d0aa3265fdc5c6ea48e8db32269b96a082b7420f7953d1d8d1ef2e6529392c7172dded9d15639fbc9c24e7bfa5cfb79e13a5498c8

10 files changed, 168 insertions, 92 deletions

diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
index df58052016..9427a9fc59 100644
--- 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 <logging/timer.h>
 #include <node/coinstats.h>
@@ -30,6 +32,7 @@
 #include <policy/rbf.h>
 #include <primitives/transaction.h>
 #include <rpc/server.h>
+#include <rpc/server_util.h>
 #include <rpc/util.h>
 #include <script/descriptor.h>
 #include <streams.h>
@@ -39,7 +42,6 @@
 #include <undo.h>
 #include <util/strencodings.h>
 #include <util/string.h>
-#include <util/system.h>
 #include <util/translation.h>
 #include <validation.h>
 #include <validationinterface.h>
@@ -64,54 +66,6 @@ static Mutex cs_blockchange;
 static std::condition_variable cond_blockchange;
 static CUpdatedBlock latestblock GUARDED_BY(cs_blockchange);
 
-NodeContext& EnsureAnyNodeContext(const std::any& context)
-{
-    auto node_context = util::AnyPtr<NodeContext>(context);
-    if (!node_context) {
-        throw JSONRPCError(RPC_INTERNAL_ERROR, "Node context not found");
-    }
-    return *node_context;
-}
-
-CTxMemPool& EnsureMemPool(const NodeContext& node)
-{
-    if (!node.mempool) {
-        throw JSONRPCError(RPC_CLIENT_MEMPOOL_DISABLED, "Mempool disabled or instance not found");
-    }
-    return *node.mempool;
-}
-
-CTxMemPool& EnsureAnyMemPool(const std::any& context)
-{
-    return EnsureMemPool(EnsureAnyNodeContext(context));
-}
-
-ChainstateManager& EnsureChainman(const NodeContext& node)
-{
-    if (!node.chainman) {
-        throw JSONRPCError(RPC_INTERNAL_ERROR, "Node chainman not found");
-    }
-    return *node.chainman;
-}
-
-ChainstateManager& EnsureAnyChainman(const std::any& context)
-{
-    return EnsureChainman(EnsureAnyNodeContext(context));
-}
-
-CBlockPolicyEstimator& EnsureFeeEstimator(const NodeContext& node)
-{
-    if (!node.fee_estimator) {
-        throw JSONRPCError(RPC_INTERNAL_ERROR, "Fee estimation disabled");
-    }
-    return *node.fee_estimator;
-}
-
-CBlockPolicyEstimator& EnsureAnyFeeEstimator(const std::any& context)
-{
-    return EnsureFeeEstimator(EnsureAnyNodeContext(context));
-}
-
 /* Calculate the difficulty for a given block index.
  */
 double GetDifficulty(const CBlockIndex* blockindex)
@@ -821,6 +775,58 @@ 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",
@@ -2704,6 +2710,7 @@ static const CRPCCommand commands[] =
     { "blockchain",         &getbestblockhash,                   },
     { "blockchain",         &getblockcount,                      },
     { "blockchain",         &getblock,                           },
+    { "blockchain",         &getblockfrompeer,                   },
     { "blockchain",         &getblockhash,                       },
     { "blockchain",         &getblockheader,                     },
     { "blockchain",         &getchaintips,                       },
diff --git a/src/rpc/blockchain.h b/src/rpc/blockchain.h
index 0ad68a7fd6..99e744fdb3 100644
--- a/src/rpc/blockchain.h
+++ b/src/rpc/blockchain.h
@@ -19,7 +19,6 @@ extern RecursiveMutex cs_main;
 
 class CBlock;
 class CBlockIndex;
-class CBlockPolicyEstimator;
 class CChainState;
 class CTxMemPool;
 class ChainstateManager;
@@ -54,14 +53,6 @@ UniValue blockheaderToJSON(const CBlockIndex* tip, const CBlockIndex* blockindex
 /** Used by getblockstats to get feerates at different percentiles by weight  */
 void CalculatePercentilesByWeight(CAmount result[NUM_GETBLOCKSTATS_PERCENTILES], std::vector<std::pair<CAmount, int64_t>>& scores, int64_t total_weight);
 
-NodeContext& EnsureAnyNodeContext(const std::any& context);
-CTxMemPool& EnsureMemPool(const NodeContext& node);
-CTxMemPool& EnsureAnyMemPool(const std::any& context);
-ChainstateManager& EnsureChainman(const NodeContext& node);
-ChainstateManager& EnsureAnyChainman(const std::any& context);
-CBlockPolicyEstimator& EnsureFeeEstimator(const NodeContext& node);
-CBlockPolicyEstimator& EnsureAnyFeeEstimator(const std::any& context);
-
 /**
  * Helper to create UTXO snapshots given a chainstate and a file handle.
  * @return a UniValue map containing metadata about the snapshot.
diff --git a/src/rpc/client.cpp b/src/rpc/client.cpp
index c0c9e4f005..a171972da3 100644
--- a/src/rpc/client.cpp
+++ b/src/rpc/client.cpp
@@ -60,6 +60,7 @@ 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" },
diff --git a/src/rpc/mining.cpp b/src/rpc/mining.cpp
index 83eab32779..371de8050d 100644
--- a/src/rpc/mining.cpp
+++ b/src/rpc/mining.cpp
@@ -20,8 +20,8 @@
 #include <pow.h>
 #include <rpc/blockchain.h>
 #include <rpc/mining.h>
-#include <rpc/net.h>
 #include <rpc/server.h>
+#include <rpc/server_util.h>
 #include <rpc/util.h>
 #include <script/descriptor.h>
 #include <script/script.h>
diff --git a/src/rpc/misc.cpp b/src/rpc/misc.cpp
index 2c05fc39fd..3716d58d4b 100644
--- a/src/rpc/misc.cpp
+++ b/src/rpc/misc.cpp
@@ -16,6 +16,7 @@
 #include <outputtype.h>
 #include <rpc/blockchain.h>
 #include <rpc/server.h>
+#include <rpc/server_util.h>
 #include <rpc/util.h>
 #include <scheduler.h>
 #include <script/descriptor.h>
diff --git a/src/rpc/net.cpp b/src/rpc/net.cpp
index 021e6ae320..bdcb339e14 100644
--- a/src/rpc/net.cpp
+++ b/src/rpc/net.cpp
@@ -9,7 +9,6 @@
 #include <chainparams.h>
 #include <clientversion.h>
 #include <core_io.h>
-#include <net.h>
 #include <net_permissions.h>
 #include <net_processing.h>
 #include <net_types.h> // For banmap_t
@@ -18,12 +17,12 @@
 #include <policy/settings.h>
 #include <rpc/blockchain.h>
 #include <rpc/protocol.h>
+#include <rpc/server_util.h>
 #include <rpc/util.h>
 #include <sync.h>
 #include <timedata.h>
 #include <util/strencodings.h>
 #include <util/string.h>
-#include <util/system.h>
 #include <util/translation.h>
 #include <validation.h>
 #include <version.h>
@@ -42,22 +41,6 @@ const std::vector<std::string> CONNECTION_TYPE_DOC{
         "feeler (short-lived automatic connection for testing addresses)"
 };
 
-CConnman& EnsureConnman(const NodeContext& node)
-{
-    if (!node.connman) {
-        throw JSONRPCError(RPC_CLIENT_P2P_DISABLED, "Error: Peer-to-peer functionality missing or disabled");
-    }
-    return *node.connman;
-}
-
-PeerManager& EnsurePeerman(const NodeContext& node)
-{
-    if (!node.peerman) {
-        throw JSONRPCError(RPC_CLIENT_P2P_DISABLED, "Error: Peer-to-peer functionality missing or disabled");
-    }
-    return *node.peerman;
-}
-
 static RPCHelpMan getconnectioncount()
 {
     return RPCHelpMan{"getconnectioncount",
diff --git a/src/rpc/net.h b/src/rpc/net.h
deleted file mode 100644
index 7a4d8440ba..0000000000
--- a/src/rpc/net.h
+++ /dev/null
@@ -1,15 +0,0 @@
-// Copyright (c) 2021 The Bitcoin Core developers
-// Distributed under the MIT software license, see the accompanying
-// file COPYING or http://www.opensource.org/licenses/mit-license.php.
-
-#ifndef BITCOIN_RPC_NET_H
-#define BITCOIN_RPC_NET_H
-
-class CConnman;
-class PeerManager;
-struct NodeContext;
-
-CConnman& EnsureConnman(const NodeContext& node);
-PeerManager& EnsurePeerman(const NodeContext& node);
-
-#endif // BITCOIN_RPC_NET_H
diff --git a/src/rpc/rawtransaction.cpp b/src/rpc/rawtransaction.cpp
index bd56e584e1..a3583e7f12 100644
--- a/src/rpc/rawtransaction.cpp
+++ b/src/rpc/rawtransaction.cpp
@@ -25,6 +25,7 @@
 #include <rpc/blockchain.h>
 #include <rpc/rawtransaction_util.h>
 #include <rpc/server.h>
+#include <rpc/server_util.h>
 #include <rpc/util.h>
 #include <script/script.h>
 #include <script/sign.h>
diff --git a/src/rpc/server_util.cpp b/src/rpc/server_util.cpp
new file mode 100644
index 0000000000..3fc35222e1
--- /dev/null
+++ b/src/rpc/server_util.cpp
@@ -0,0 +1,80 @@
+// Copyright (c) 2021 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <rpc/server_util.h>
+
+#include <net_processing.h>
+#include <node/context.h>
+#include <policy/fees.h>
+#include <rpc/protocol.h>
+#include <rpc/request.h>
+#include <txmempool.h>
+#include <util/system.h>
+#include <validation.h>
+
+#include <any>
+
+NodeContext& EnsureAnyNodeContext(const std::any& context)
+{
+    auto node_context = util::AnyPtr<NodeContext>(context);
+    if (!node_context) {
+        throw JSONRPCError(RPC_INTERNAL_ERROR, "Node context not found");
+    }
+    return *node_context;
+}
+
+CTxMemPool& EnsureMemPool(const NodeContext& node)
+{
+    if (!node.mempool) {
+        throw JSONRPCError(RPC_CLIENT_MEMPOOL_DISABLED, "Mempool disabled or instance not found");
+    }
+    return *node.mempool;
+}
+
+CTxMemPool& EnsureAnyMemPool(const std::any& context)
+{
+    return EnsureMemPool(EnsureAnyNodeContext(context));
+}
+
+ChainstateManager& EnsureChainman(const NodeContext& node)
+{
+    if (!node.chainman) {
+        throw JSONRPCError(RPC_INTERNAL_ERROR, "Node chainman not found");
+    }
+    return *node.chainman;
+}
+
+ChainstateManager& EnsureAnyChainman(const std::any& context)
+{
+    return EnsureChainman(EnsureAnyNodeContext(context));
+}
+
+CBlockPolicyEstimator& EnsureFeeEstimator(const NodeContext& node)
+{
+    if (!node.fee_estimator) {
+        throw JSONRPCError(RPC_INTERNAL_ERROR, "Fee estimation disabled");
+    }
+    return *node.fee_estimator;
+}
+
+CBlockPolicyEstimator& EnsureAnyFeeEstimator(const std::any& context)
+{
+    return EnsureFeeEstimator(EnsureAnyNodeContext(context));
+}
+
+CConnman& EnsureConnman(const NodeContext& node)
+{
+    if (!node.connman) {
+        throw JSONRPCError(RPC_CLIENT_P2P_DISABLED, "Error: Peer-to-peer functionality missing or disabled");
+    }
+    return *node.connman;
+}
+
+PeerManager& EnsurePeerman(const NodeContext& node)
+{
+    if (!node.peerman) {
+        throw JSONRPCError(RPC_CLIENT_P2P_DISABLED, "Error: Peer-to-peer functionality missing or disabled");
+    }
+    return *node.peerman;
+}
diff --git a/src/rpc/server_util.h b/src/rpc/server_util.h
new file mode 100644
index 0000000000..ad3c149c90
--- /dev/null
+++ b/src/rpc/server_util.h
@@ -0,0 +1,27 @@
+// Copyright (c) 2021 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_RPC_SERVER_UTIL_H
+#define BITCOIN_RPC_SERVER_UTIL_H
+
+#include <any>
+
+class CBlockPolicyEstimator;
+class CConnman;
+class ChainstateManager;
+class CTxMemPool;
+struct NodeContext;
+class PeerManager;
+
+NodeContext& EnsureAnyNodeContext(const std::any& context);
+CTxMemPool& EnsureMemPool(const NodeContext& node);
+CTxMemPool& EnsureAnyMemPool(const std::any& context);
+ChainstateManager& EnsureChainman(const NodeContext& node);
+ChainstateManager& EnsureAnyChainman(const std::any& context);
+CBlockPolicyEstimator& EnsureFeeEstimator(const NodeContext& node);
+CBlockPolicyEstimator& EnsureAnyFeeEstimator(const std::any& context);
+CConnman& EnsureConnman(const NodeContext& node);
+PeerManager& EnsurePeerman(const NodeContext& node);
+
+#endif // BITCOIN_RPC_SERVER_UTIL_H