Add block pruning functionality

This adds a -prune=N option to bitcoind, which if set to N>0 will enable block
file pruning. When pruning is enabled, block and undo files will be deleted to
try to keep total space used by those files to below the prune target (N, in
MB) specified by the user, subject to some constraints:

- The last 288 blocks on the main chain are always kept (MIN_BLOCKS_TO_KEEP),
- N must be at least 550MB (chosen as a value for the target that could
  reasonably be met, with some assumptions about block sizes, orphan rates,
  etc; see comment in main.h),
- No blocks are pruned until chainActive is at least 100,000 blocks long (on
  mainnet; defined separately for mainnet, testnet, and regtest in chainparams
  as nPruneAfterHeight).

This unsets NODE_NETWORK if pruning is enabled.

Also included is an RPC test for pruning (pruning.py).

Thanks to @rdponticelli for earlier work on this feature; this is based in
part off that work.

1 files changed, 86 insertions, 4 deletions

diff --git a/src/init.cpp b/src/init.cpp
index 665aebe1c5..b648a237bf 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -275,7 +275,12 @@ std::string HelpMessage(HelpMessageMode mode)
 #ifndef WIN32
     strUsage += HelpMessageOpt("-pid=<file>", strprintf(_("Specify pid file (default: %s)"), "bitcoind.pid"));
 #endif
-    strUsage += HelpMessageOpt("-reindex", _("Rebuild block chain index from current blk000??.dat files") + " " + _("on startup"));
+    strUsage += HelpMessageOpt("-prune=<n>", _("Reduce storage requirements by pruning (deleting) old blocks. This mode disables wallet support and is incompatible with -txindex.") + " " +
+            _("Warning: Reverting this setting requires re-downloading the entire blockchain.") + " " +
+            _("(default: 0 = disable pruning blocks,") + " " +
+            strprintf(_(">%u = target size in MiB to use for block files)"), MIN_DISK_SPACE_FOR_BLOCK_FILES / 1024 / 1024));
+strUsage += HelpMessageOpt("-reindex", _("Rebuild block chain index from current blk000??.dat files") + " " + _("on startup"));
+
 #if !defined(WIN32)
     strUsage += HelpMessageOpt("-sysperms", _("Create new files with system default permissions, instead of umask 077 (only effective with disabled wallet functionality)"));
 #endif
@@ -352,7 +357,7 @@ std::string HelpMessage(HelpMessageMode mode)
         strUsage += HelpMessageOpt("-flushwallet", strprintf(_("Run a thread to flush wallet periodically (default: %u)"), 1));
         strUsage += HelpMessageOpt("-stopafterblockimport", strprintf(_("Stop running after importing blocks from disk (default: %u)"), 0));
     }
-    string debugCategories = "addrman, alert, bench, coindb, db, lock, rand, rpc, selectcoins, mempool, net, proxy"; // Don't translate these and qt below
+    string debugCategories = "addrman, alert, bench, coindb, db, lock, rand, rpc, selectcoins, mempool, net, proxy, prune"; // Don't translate these and qt below
     if (mode == HMM_BITCOIN_QT)
         debugCategories += ", qt";
     strUsage += HelpMessageOpt("-debug=<category>", strprintf(_("Output debugging information (default: %u, supplying <category> is optional)"), 0) + ". " +
@@ -458,10 +463,33 @@ struct CImportingNow
     }
 };
 
+
+// If we're using -prune with -reindex, then delete block files that will be ignored by the
+// reindex.  Since reindexing works by starting at block file 0 and looping until a blockfile
+// is missing, and since pruning works by deleting the oldest block file first, just check
+// for block file 0, and if it doesn't exist, delete all the block files in the
+// directory (since they won't be read by the reindex but will take up disk space).
+void DeleteAllBlockFiles()
+{
+    if (boost::filesystem::exists(GetBlockPosFilename(CDiskBlockPos(0, 0), "blk")))
+        return;
+
+    LogPrintf("Removing all blk?????.dat and rev?????.dat files for -reindex with -prune\n");
+    boost::filesystem::path blocksdir = GetDataDir() / "blocks";
+    for (boost::filesystem::directory_iterator it(blocksdir); it != boost::filesystem::directory_iterator(); it++) {
+        if (is_regular_file(*it)) {
+            if ((it->path().filename().string().length() == 12) &&
+                (it->path().filename().string().substr(8,4) == ".dat") &&
+                ((it->path().filename().string().substr(0,3) == "blk") ||
+                 (it->path().filename().string().substr(0,3) == "rev")))
+                boost::filesystem::remove(it->path());
+        }
+    }
+}
+
 void ThreadImport(std::vector<boost::filesystem::path> vImportFiles)
 {
     RenameThread("bitcoin-loadblk");
-
     // -reindex
     if (fReindex) {
         CImportingNow imp;
@@ -674,6 +702,21 @@ bool AppInit2(boost::thread_group& threadGroup)
     if (nFD - MIN_CORE_FILEDESCRIPTORS < nMaxConnections)
         nMaxConnections = nFD - MIN_CORE_FILEDESCRIPTORS;
 
+    // if using block pruning, then disable txindex
+    // also disable the wallet (for now, until SPV support is implemented in wallet)
+    if (GetArg("-prune", 0)) {
+        if (GetBoolArg("-txindex", false))
+            return InitError(_("Prune mode is incompatible with -txindex."));
+#ifdef ENABLE_WALLET
+        if (!GetBoolArg("-disablewallet", false)) {
+            if (SoftSetBoolArg("-disablewallet", true))
+                LogPrintf("%s : parameter interaction: -prune -> setting -disablewallet=1\n", __func__);
+            else
+                return InitError(_("Can't run with a wallet in prune mode."));
+        }
+#endif
+    }
+
     // ********************************************************* Step 3: parameter-to-internal-flags
 
     fDebug = !mapMultiArgs["-debug"].empty();
@@ -710,6 +753,21 @@ bool AppInit2(boost::thread_group& threadGroup)
         nScriptCheckThreads = MAX_SCRIPTCHECK_THREADS;
 
     fServer = GetBoolArg("-server", false);
+
+    // block pruning; get the amount of disk space (in MB) to allot for block & undo files
+    int64_t nSignedPruneTarget = GetArg("-prune", 0) * 1024 * 1024;
+    if (nSignedPruneTarget < 0) {
+        return InitError(_("Prune cannot be configured with a negative value."));
+    }
+    nPruneTarget = (uint64_t) nSignedPruneTarget;
+    if (nPruneTarget) {
+        if (nPruneTarget < MIN_DISK_SPACE_FOR_BLOCK_FILES) {
+            return InitError(strprintf(_("Prune configured below the minimum of %d MB.  Please use a higher number."), MIN_DISK_SPACE_FOR_BLOCK_FILES / 1024 / 1024));
+        }
+        LogPrintf("Prune configured to target %uMiB on disk for block and undo files.\n", nPruneTarget / 1024 / 1024);
+        fPruneMode = true;
+    }
+
 #ifdef ENABLE_WALLET
     bool fDisableWallet = GetBoolArg("-disablewallet", false);
 #endif
@@ -1030,8 +1088,12 @@ bool AppInit2(boost::thread_group& threadGroup)
                 pcoinscatcher = new CCoinsViewErrorCatcher(pcoinsdbview);
                 pcoinsTip = new CCoinsViewCache(pcoinscatcher);
 
-                if (fReindex)
+                if (fReindex) {
                     pblocktree->WriteReindexing(true);
+                    //If we're reindexing in prune mode, wipe away all our block and undo data files
+                    if (fPruneMode)
+                        DeleteAllBlockFiles();
+                }
 
                 if (!LoadBlockIndex()) {
                     strLoadError = _("Error loading block database");
@@ -1055,7 +1117,18 @@ bool AppInit2(boost::thread_group& threadGroup)
                     break;
                 }
 
+                // Check for changed -prune state.  What we are concerned about is a user who has pruned blocks
+                // in the past, but is now trying to run unpruned.
+                if (fHavePruned && !fPruneMode) {
+                    strLoadError = _("You need to rebuild the database using -reindex to go back to unpruned mode.  This will redownload the entire blockchain");
+                    break;
+                }
+
                 uiInterface.InitMessage(_("Verifying blocks..."));
+                if (fHavePruned && GetArg("-checkblocks", 288) > MIN_BLOCKS_TO_KEEP) {
+                    LogPrintf("Prune: pruned datadir may not have more than %d blocks; -checkblocks=%d may fail\n",
+                        MIN_BLOCKS_TO_KEEP, GetArg("-checkblocks", 288));
+                }
                 if (!CVerifyDB().VerifyDB(pcoinsdbview, GetArg("-checklevel", 3),
                               GetArg("-checkblocks", 288))) {
                     strLoadError = _("Corrupted block database detected");
@@ -1106,6 +1179,15 @@ bool AppInit2(boost::thread_group& threadGroup)
         mempool.ReadFeeEstimates(est_filein);
     fFeeEstimatesInitialized = true;
 
+    // if prune mode, unset NODE_NETWORK and prune block files
+    if (fPruneMode) {
+        LogPrintf("Unsetting NODE_NETWORK on prune mode\n");
+        nLocalServices &= ~NODE_NETWORK;
+        if (!fReindex) {
+            PruneAndFlush();
+        }
+    }
+
     // ********************************************************* Step 8: load wallet
 #ifdef ENABLE_WALLET
     if (fDisableWallet) {