Restore NODE_NETWORK functionality with trim_headers

Author: psgreco

src/init.cpp

@@ -987,7 +987,7 @@ bool AppInitParameterInteraction(const ArgsManager& args)
     }
 
     if (args.GetBoolArg("-trim_headers", false)) {
-        LogPrintf("Configured for header-trimming mode. This will reduce memory usage substantially, but we will be unable to serve as a full P2P peer, and certain header fields may be missing from JSON RPC output.\n");
+        LogPrintf("Configured for header-trimming mode. This will reduce memory usage substantially, but will increase IO usage when the headers need to be temporarily untrimmed.\n");
         fTrimHeaders = true;
         // This calculation is driven by GetValidFedpegScripts in pegins.cpp, which walks the chain
         //   back to current epoch start, and then an additional total_valid_epochs on top of that.
@@ -1711,7 +1711,7 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
 
     // if pruning, unset the service bit and perform the initial blockstore prune
     // after any wallet rescanning has taken place.
-    if (fPruneMode || fTrimHeaders) {
+    if (fPruneMode) {
         LogPrintf("Unsetting NODE_NETWORK on prune mode\n");
         nLocalServices = ServiceFlags(nLocalServices & ~NODE_NETWORK);
         if (!fReindex) {
@@ -1723,11 +1723,6 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
         }
     }
 
-    if (fTrimHeaders) {
-        LogPrintf("Unsetting NODE_NETWORK_LIMITED on header trim mode\n");
-        nLocalServices = ServiceFlags(nLocalServices & ~NODE_NETWORK_LIMITED);
-    }
-
     if (DeploymentEnabled(chainparams.GetConsensus(), Consensus::DEPLOYMENT_SEGWIT)) {
         // Advertise witness capabilities.
         // The option to not set NODE_WITNESS is only used in the tests and should be removed.

src/net_processing.cpp

@@ -3183,12 +3183,13 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
         for (; pindex; pindex = m_chainman.ActiveChain().Next(pindex))
         {
             if (pindex->trimmed()) {
-                // For simplicity, if any of the headers they're asking for are trimmed,
-                //   just drop the request.
-                LogPrint(BCLog::NET, "%s: ignoring getheaders from peer=%i which would return at least one trimmed header\n", __func__, pfrom.GetId());
-                return;
+                // Header is trimmed, reload from disk before sending
+                CBlockIndex tmpBlockIndexFull;
+                const CBlockIndex* pindexfull = pindex->untrim_to(&tmpBlockIndexFull);
+                vHeaders.push_back(pindexfull->GetBlockHeader());
+            } else {
+                vHeaders.push_back(pindex->GetBlockHeader());
             }
-            vHeaders.push_back(pindex->GetBlockHeader());
             if (--nLimit <= 0 || pindex->GetBlockHash() == hashStop)
                 break;
         }