rpc: warn that nodes ignore requests for old stale blocks

This is an anti-fingerprinting measure. See BlockRequestAllowed in net_processing. It has been around since 2014, but alternative clients might still serve these blocks. See also: d8b4b49, 85da07a, a2be3b6, 3788a84
PastaPastaPasta · Sep 6, 2022 · f39d926 · f39d926
1 parent 5291933
commit f39d926
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Showing 2 changed files with 5 additions and 1 deletion.
diff --git a/src/net_processing.cpp b/src/net_processing.cpp
@@ -1738,6 +1738,8 @@ std::optional<std::string> PeerManagerImpl::FetchBlock(NodeId peer_id, const CBl
     LOCK(cs_main);
 
     // Mark block as in-flight unless it already is (for this peer).
+    // If the peer does not send us a block, vBlocksInFlight remains non-empty,
+    // causing us to timeout and disconnect.
     // If a block was already in-flight for a different peer, its BLOCKTXN
     // response will be dropped.
     if (!BlockRequested(peer_id, block_index)) return "Already requested from this peer";

diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
@@ -428,7 +428,9 @@ static RPCHelpMan getblockfrompeer()
         "getblockfrompeer",
         "Attempt to fetch block from a given peer.\n\n"
         "We 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\n"
+        "Subsequent calls for the same block and a new peer will cause the response from the previous peer to be ignored.\n"
+        "Peers generally ignore requests for a stale block that they never fully verified, or one that is more than a month old.\n"
+        "When a peer does not respond with a block, we will disconnect.\n\n"
         "Returns an empty JSON object if the request was successfully scheduled.",
         {
             {"blockhash", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The block hash to try to fetch"},