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changeset 2994:392e97abcb40 draft

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Prevent stuck block download in large reorganisations In cases of very large reorganisations (hundreds of blocks), a situation may appear where an 'inv' is sent as response to a 'getblocks', but the last block mentioned in the inv is already known to the receiver node. However, the supplying node uses a request for this last block as a trigger to send the rest of the inv blocks. If it never comes, the block chain download is stuck. This commit makes the receiver node always request the last inv'ed block, even if it is already known, to prevent this problem.
author Pieter Wuille <pieter.wuille@gmail.com>
date Sun, 18 Mar 2012 23:47:26 +0100
parents 303fa0657007
children dd5a9271101d
files src/main.cpp
diffstat 1 files changed, 8 insertions(+), 3 deletions(-) [+]
line wrap: on
line diff
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -2178,8 +2178,10 @@
             return error("message inv size() = %d", vInv.size());
 
         CTxDB txdb("r");
-        BOOST_FOREACH(const CInv& inv, vInv)
+        for (int nInv = 0; nInv < vInv.size(); nInv++)
         {
+            const CInv &inv = vInv[nInv];
+
             if (fShutdown)
                 return true;
             pfrom->AddInventoryKnown(inv);
@@ -2188,9 +2190,12 @@
             if (fDebug)
                 printf("  got inventory: %s  %s\n", inv.ToString().c_str(), fAlreadyHave ? "have" : "new");
 
-            if (!fAlreadyHave)
+            // Always request the last block in an inv bundle (even if we already have it), as it is the
+            // trigger for the other side to send further invs. If we are stuck on a (very long) side chain,
+            // this is necessary to connect earlier received orphan blocks to the chain again.
+            if (!fAlreadyHave || (inv.type == MSG_BLOCK && nInv==vInv.size()-1))
                 pfrom->AskFor(inv);
-            else if (inv.type == MSG_BLOCK && mapOrphanBlocks.count(inv.hash))
+            if (inv.type == MSG_BLOCK && mapOrphanBlocks.count(inv.hash))
                 pfrom->PushGetBlocks(pindexBest, GetOrphanRoot(mapOrphanBlocks[inv.hash]));
 
             // Track requests for our stuff