bitcoincore read block snippet

read_block.cpp

// rest.cpp

// will be called with http request /rest/block/[BLOCK_HASH_VALUE]
static bool rest_block(HTTPRequest* req, const std::string& strURIPart, bool showTxDetails)
{
  // ...
  uint256 hash; // will be parsed from `strURIPart`
  
  CBlock block;
  CBlockIndex* pblockindex = nullptr;
  {
    LOCK(cs_main);
    if (mapBlockIndex.count(hash) == 0)
      return RESTERR(req, HTTP_NOT_FOUND, hashStr + " not found");

    pblockindex = mapBlockIndex[hash];
    if (fHavePruned && !(pblockindex->nStatus & BLOCK_HAVE_DATA) && pblockindex->nTx > 0)
      return RESTERR(req, HTTP_NOT_FOUND, hashStr + " not available (pruned data)");

    if (!ReadBlockFromDisk(block, pblockindex, Params().GetConsensus()))
      return RESTERR(req, HTTP_NOT_FOUND, hashStr + " not found");
  }
  // ...
}

// validation.cpp
// in-memory block index
typedef std::unordered_map<uint256, CBlockIndex*, BlockHasher> BlockMap;
BlockMap mapBlockIndex;


bool ReadBlockFromDisk(CBlock& block, const CBlockIndex* pindex, const Consensus::Params& consensusParams)
{
  // pindex->GetBlockPos() returns nFile(file number) and nDataPos(offset in the file)
  if (!ReadBlockFromDisk(block, pindex->GetBlockPos(), consensusParams))
    return false;
  // ...
}

bool ReadBlockFromDisk(CBlock& block, const CDiskBlockPos& pos, const Consensus::Params& consensusParams)
{
    block.SetNull();

    // Open history file to read
    CAutoFile filein(OpenBlockFile(pos, true), SER_DISK, CLIENT_VERSION);
    // ...
    // Read block
    try {
        filein >> block;
    }
    catch (const std::exception& e) {
      // ...
    }
    // ...
}

FILE* OpenBlockFile(const CDiskBlockPos &pos, bool fReadOnly) {
    return OpenDiskFile(pos, "blk", fReadOnly);
}

static FILE* OpenDiskFile(const CDiskBlockPos &pos, const char *prefix, bool fReadOnly)
{
  // ...
  fs::path path = GetBlockPosFilename(pos, prefix);
  // => GetDataDir() / "blocks" / strprintf("%s%05u.dat", prefix, pos.nFile);

  // ...
  FILE* file = fsbridge::fopen(path, fReadOnly ? "rb": "rb+");
  // ...
  if (pos.nPos) {
    if (fseek(file, pos.nPos, SEEK_SET)) {
      // ...
    }
  }
  return file;
}