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

1 files changed, 56 insertions, 49 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,                       },