Add a flag for header-trimming; clear P2P network feature bits when enabled.

Author: gwillen

src/init.cpp

@@ -425,6 +425,7 @@ void SetupServerArgs(ArgsManager& argsman)
     hidden_args.emplace_back("-sysperms");
 #endif
     argsman.AddArg("-txindex", strprintf("Maintain a full transaction index, used by the getrawtransaction rpc call (default: %u)", DEFAULT_TXINDEX), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
+    argsman.AddArg("-trim_headers", strprintf("Trim old headers in memory, removing blocksigning and dynafed-related fields. Saves memory, but blocks us from serving blocks or headers to peers, and removes trimmed fields from some JSON RPC outputs. (default: false)"), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-blockfilterindex=<type>",
                  strprintf("Maintain an index of compact filters by block (default: %s, values: %s).", DEFAULT_BLOCKFILTERINDEX, ListBlockFilterTypes()) +
                  " If <type> is not supplied or if <type> = 1, indexes for all known types are enabled.",
@@ -979,6 +980,23 @@ bool AppInitParameterInteraction(const ArgsManager& args)
         fPruneMode = true;
     }
 
+    if (args.IsArgSet("-trim_headers")) {
+        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");
+        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.
+        //   We add one epoch here for the current partial epoch, and then another one for good luck.
+        // NB: If we're non-dynafed, then:
+        //   - total_valid_epochs = 1
+        //   - dynamic_epoch_length = std::numeric_limits<uint32_t>::max()
+        //   So this will work out to an unhelpfully-large number. XXX: Is this a problem?
+        nMustKeepFullHeaders = (chainparams.GetConsensus().total_valid_epochs + 2) * (chainparams.GetConsensus().dynamic_epoch_length);
+        // This is the number of headers we can have in flight downloading at a time, beyond the
+        //   set of blocks we've already validated. Capping this is necessary to keep memory usage
+        //   bounded during IBD.
+    }
+    nHeaderDownloadBuffer = chainparams.GetConsensus().dynamic_epoch_length * 2;
+
     nConnectTimeout = args.GetArg("-timeout", DEFAULT_CONNECT_TIMEOUT);
     if (nConnectTimeout <= 0) {
         nConnectTimeout = DEFAULT_CONNECT_TIMEOUT;
@@ -1690,7 +1708,7 @@ 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) {
+    if (fPruneMode || fTrimHeaders) {
         LogPrintf("Unsetting NODE_NETWORK on prune mode\n");
         nLocalServices = ServiceFlags(nLocalServices & ~NODE_NETWORK);
         if (!fReindex) {
@@ -1702,6 +1720,11 @@ 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/node/blockstorage.cpp

@@ -25,6 +25,9 @@ std::atomic_bool fReindex(false);
 bool fHavePruned = false;
 bool fPruneMode = false;
 uint64_t nPruneTarget = 0;
+bool fTrimHeaders = false;
+uint64_t nMustKeepFullHeaders = std::numeric_limits<uint64_t>::max();
+uint64_t nHeaderDownloadBuffer = std::numeric_limits<uint64_t>::max();
 
 // TODO make namespace {
 RecursiveMutex cs_LastBlockFile;

src/node/blockstorage.h

@@ -44,6 +44,13 @@ extern bool fHavePruned;
 extern bool fPruneMode;
 /** Number of MiB of block files that we're trying to stay below. */
 extern uint64_t nPruneTarget;
+/** True if we're running in -trim_headers mode. */
+extern bool fTrimHeaders;
+/** Minimum number of full untrimmed headers to keep, for blocks we have. */
+extern uint64_t nMustKeepFullHeaders;
+/** Target number of headers to download beyond the blocks we have. */
+// XXX: this currently only operates when in header trim mode, but it's really independent of that.
+extern uint64_t nHeaderDownloadBuffer;
 
 //! Check whether the block associated with this index entry is pruned or not.
 bool IsBlockPruned(const CBlockIndex* pblockindex);