Re: Understanding The Satoshi Codebase (Series) PART 1 -

Block Checking & Submit Blocks

File - main.cpp
Line - 1154 -1295

Code:

bool CBlock::CheckBlock() const
{
These are checks that are independent of context
that can be verified before saving an orphan block.

// This section checks the Size limits

Code:

if (vtx.empty() || vtx.size() > MAX_SIZE || ::GetSerializeSize(*this, SER_DISK) > MAX_SIZE)
return error("CheckBlock() : size limits failed");

// This section of code if for checking the timestamp of the block, a timestamp is valid if it is greater than the median timestamp of last 11 blocks and less than the network-adjusted time + 2 hours

Code:

if (nTime > GetAdjustedTime() + 2 * 60 * 60)
return error("CheckBlock() : block timestamp too far in the future");

// This section checks to make sure the first transaction is a coinbase transaction and everything else is not a coinbase TX

Code:

if (vtx.empty() || !vtx[0].IsCoinBase())
   return error("CheckBlock() : first tx is not coinbase");
   for (int i = 1; i < vtx.size(); i++)
   if (vtx[i].IsCoinBase())
   return error("CheckBlock() : more than one coinbase");

// Check transactions

Code:

foreach(const CTransaction& tx, vtx)
if (!tx.CheckTransaction())
return error("CheckBlock() : CheckTransaction failed");

// This section checks that the proof of work matches claimed amount

Code:

if (CBigNum().SetCompact(nBits) > bnProofOfWorkLimit)
   return error("CheckBlock() : nBits below minimum work");
   if (GetHash() > CBigNum().SetCompact(nBits).getuint256())
   return error("CheckBlock() : hash doesn't match nBits");

// It is then passed to check the merkleroot

Code:

if (hashMerkleRoot != BuildMerkleTree())
return error("CheckBlock() : hashMerkleRoot mismatch");

return true;
}

Now the code will check for AcceptBlock by checking the following aspects.

bool CBlock::AcceptBlock()

// In this section the code performs a check for duplicate block.

Code:

uint256 hash = GetHash();
if (mapBlockIndex.count(hash))
return error("AcceptBlock() : block already in mapBlockIndex");

// Here the code will get the previous block index

Code:

map::iterator mi = mapBlockIndex.find(hashPrevBlock);
   if (mi == mapBlockIndex.end())
   return error("AcceptBlock() : prev block not found");
   CBlockIndex* pindexPrev = (*mi).second;

// It will then check the timestamp against previous block

Code:

if (nTime <= pindexPrev->GetMedianTimePast())
return error("AcceptBlock() : block's timestamp is too early");

// It then performs a check on the proof of work

Code:

if (nBits != GetNextWorkRequired(pindexPrev))
return error("AcceptBlock() : incorrect proof of work");

// Here the code will write the block to history file

Code:

if (!CheckDiskSpace(::GetSerializeSize(*this, SER_DISK)))
   return error("AcceptBlock() : out of disk space");
   unsigned int nFile;
   unsigned int nBlockPos;
   if (!WriteToDisk(!fClient, nFile, nBlockPos))
   return error("AcceptBlock() : WriteToDisk failed");
   if (!AddToBlockIndex(nFile, nBlockPos))
   return error("AcceptBlock() : AddToBlockIndex failed");

   if (hashBestChain == hash)
   RelayInventory(CInv(MSG_BLOCK, hash));

The next section is commented out of the code and I am still looking for some references for the code below and relations to VAtoms.

// // Add atoms to user reviews for coins created

Code:

// vector vchPubKey;
   // if (ExtractPubKey(vtx[0].vout[0].scriptPubKey, false, vchPubKey))
   // {
   // unsigned short nAtom = GetRand(USHRT_MAX - 100) + 100;
   // vector vAtoms(1, nAtom);
   // AddAtomsAndPropagate(Hash(vchPubKey.begin(), vchPubKey.end()), vAtoms, true);
   // }

   return true;
}

Next the code looks to process the block by the following.

bool ProcessBlock(CNode* pfrom, CBlock* pblock)

// Check for duplicate

Code:

uint256 hash = pblock->GetHash();
   if (mapBlockIndex.count(hash))
   return error("ProcessBlock() : already have block %d %s", mapBlockIndex[hash]->nHeight, hash.ToString().substr(0,14).c_str());
   if (mapOrphanBlocks.count(hash))
   return error("ProcessBlock() : already have block (orphan) %s", hash.ToString().substr(0,14).c_str());

// Preliminary checks

Code:

if (!pblock->CheckBlock())
   {
   delete pblock;
   return error("ProcessBlock() : CheckBlock FAILED");
   }

// If don't already have its previous block, shunt it off to holding area until we get it

Code:

if (!mapBlockIndex.count(pblock->hashPrevBlock))
   {
   printf("ProcessBlock: ORPHAN BLOCK, prev=%s\n", pblock->hashPrevBlock.ToString().substr(0,14).c_str());
   mapOrphanBlocks.insert(make_pair(hash, pblock));
   mapOrphanBlocksByPrev.insert(make_pair(pblock->hashPrevBlock, pblock));

// Ask this guy to fill in what we're missing

Code:

if (pfrom)
   pfrom->PushMessage("getblocks", CBlockLocator(pindexBest), GetOrphanRoot(pblock));
   return true;
   }

// Store to disk

Code:

if (!pblock->AcceptBlock())
   {
   delete pblock;
   return error("ProcessBlock() : AcceptBlock FAILED");
   }
   delete pblock;

// Recursively process any orphan blocks that depended on this one

Code:

vector vWorkQueue;
   vWorkQueue.push_back(hash);
   for (int i = 0; i < vWorkQueue.size(); i++)
   {
   uint256 hashPrev = vWorkQueue[i];
   for (multimap::iterator mi = mapOrphanBlocksByPrev.lower_bound(hashPrev);
   mi != mapOrphanBlocksByPrev.upper_bound(hashPrev);
   ++mi)
   {
   CBlock* pblockOrphan = (*mi).second;
   if (pblockOrphan->AcceptBlock())
   vWorkQueue.push_back(pblockOrphan->GetHash());
   mapOrphanBlocks.erase(pblockOrphan->GetHash());
   delete pblockOrphan;
   }
   mapOrphanBlocksByPrev.erase(hashPrev);
   }

At this point the miner would be very happy! as the block has passed the checked and can be called Valid.
The code then prints below :

Code:

printf("ProcessBlock: ACCEPTED\n");
return true;