validation: Use span for CalculateClaimedHeadersWork

Makes it friendlier for potential future users of the kernel library if
they do not store the headers in a std::vector, but can guarantee
contiguous memory.

src/net_processing.cpp

@@ -4751,7 +4751,7 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
                 MaybeSendGetHeaders(pfrom, GetLocator(m_chainman.m_best_header), *peer);
             }
             return;
-        } else if (prev_block->nChainWork + CalculateClaimedHeadersWork({cmpctblock.header}) < GetAntiDoSWorkThreshold()) {
+        } else if (prev_block->nChainWork + CalculateClaimedHeadersWork({{cmpctblock.header}}) < GetAntiDoSWorkThreshold()) {
             // If we get a low-work header in a compact block, we can ignore it.
             LogPrint(BCLog::NET, "Ignoring low-work compact block from peer %d\n", pfrom.GetId());
             return;
@@ -5068,7 +5068,7 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
             mapBlockSource.emplace(hash, std::make_pair(pfrom.GetId(), true));
 
             // Check claimed work on this block against our anti-dos thresholds.
-            if (prev_block && prev_block->nChainWork + CalculateClaimedHeadersWork({pblock->GetBlockHeader()}) >= GetAntiDoSWorkThreshold()) {
+            if (prev_block && prev_block->nChainWork + CalculateClaimedHeadersWork({{pblock->GetBlockHeader()}}) >= GetAntiDoSWorkThreshold()) {
                 min_pow_checked = true;
             }
         }

src/validation.cpp

@@ -4137,7 +4137,7 @@ bool IsBlockMutated(const CBlock& block, bool check_witness_root)
     return false;
 }
 
-arith_uint256 CalculateClaimedHeadersWork(const std::vector<CBlockHeader>& headers)
+arith_uint256 CalculateClaimedHeadersWork(std::span<const CBlockHeader> headers)
 {
     arith_uint256 total_work{0};
     for (const CBlockHeader& header : headers) {

src/validation.h

@@ -408,7 +408,7 @@ bool HasValidProofOfWork(const std::vector<CBlockHeader>& headers, const Consens
 bool IsBlockMutated(const CBlock& block, bool check_witness_root);
 
 /** Return the sum of the claimed work on a given set of headers. No verification of PoW is done. */
-arith_uint256 CalculateClaimedHeadersWork(const std::vector<CBlockHeader>& headers);
+arith_uint256 CalculateClaimedHeadersWork(std::span<const CBlockHeader> headers);
 
 enum class VerifyDBResult {
     SUCCESS,