Limit response to getblocks to half of output buffer size

Introduce SendBufferSize() and ReceiveBufferSize(), and limit
the blocks sent as response to the "getblocks" message to
half of the active send buffer size.

src/main.cpp

@@ -2040,20 +2040,24 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv)
         if (pindex)
             pindex = pindex->pnext;
         int nLimit = 500 + locator.GetDistanceBack();
+        unsigned int nBytes = 0;
         printf("getblocks %d to %s limit %d\n", (pindex ? pindex->nHeight : -1), hashStop.ToString().substr(0,20).c_str(), nLimit);
         for (; pindex; pindex = pindex->pnext)
         {
             if (pindex->GetBlockHash() == hashStop)
             {
-                printf("  getblocks stopping at %d %s\n", pindex->nHeight, pindex->GetBlockHash().ToString().substr(0,20).c_str());
+                printf("  getblocks stopping at %d %s (%u bytes)\n", pindex->nHeight, pindex->GetBlockHash().ToString().substr(0,20).c_str(), nBytes);
                 break;
             }
             pfrom->PushInventory(CInv(MSG_BLOCK, pindex->GetBlockHash()));
-            if (--nLimit <= 0)
+            CBlock block;
+            block.ReadFromDisk(pindex, true);
+            nBytes += block.GetSerializeSize(SER_NETWORK);
+            if (--nLimit <= 0 || nBytes >= SendBufferSize()/2)
             {
                 // When this block is requested, we'll send an inv that'll make them
                 // getblocks the next batch of inventory.
-                printf("  getblocks stopping at limit %d %s\n", pindex->nHeight, pindex->GetBlockHash().ToString().substr(0,20).c_str());
+                printf("  getblocks stopping at limit %d %s (%u bytes)\n", pindex->nHeight, pindex->GetBlockHash().ToString().substr(0,20).c_str(), nBytes);
                 pfrom->hashContinue = pindex->GetBlockHash();
                 break;
             }

src/net.cpp

@@ -915,7 +915,7 @@ void ThreadSocketHandler2(void* parg)
                     CDataStream& vRecv = pnode->vRecv;
                     unsigned int nPos = vRecv.size();
 
-                    if (nPos > 1000*GetArg("-maxreceivebuffer", 10*1000)) {
+                    if (nPos > ReceiveBufferSize()) {
                         if (!pnode->fDisconnect)
                             printf("socket recv flood control disconnect (%d bytes)\n", vRecv.size());
                         pnode->CloseSocketDisconnect();
@@ -980,7 +980,7 @@ void ThreadSocketHandler2(void* parg)
                                 pnode->CloseSocketDisconnect();
                             }
                         }
-                        if (vSend.size() > 1000*GetArg("-maxsendbuffer", 10*1000)) {
+                        if (vSend.size() > SendBufferSize()) {
                             if (!pnode->fDisconnect)
                                 printf("socket send flood control disconnect (%d bytes)\n", vSend.size());
                             pnode->CloseSocketDisconnect();

src/net.h

@@ -23,6 +23,8 @@ extern int nConnectTimeout;
 
 
 
+inline unsigned int ReceiveBufferSize() { return 1000*GetArg("-maxreceivebuffer", 10*1000); }
+inline unsigned int SendBufferSize() { return 1000*GetArg("-maxsendbuffer", 10*1000); }
 inline unsigned short GetDefaultPort() { return fTestNet ? 18333 : 8333; }
 static const unsigned int PUBLISH_HOPS = 5;
 enum