ProtectionAreas (built-in)

[DiamondToaster]

So, something like:

class cBlockToEntityData
{
    public:
        Vector3i Position;
        int GetBlockType(); // returns E_BLOCK type
        int GetMetaData(); // returns E_META data
        cBlockInfo GetBlockInfo(); // returns a cBlockInfo
        // Excuse my lack of knowledge of the internals of MCServer...
}

Then the Lua bindings would send table full of these:

function OnExploding(World, ExplosionSize, CanCauseFire, X, Y, Z, Source, SourceData, AffectedBlocks)
    -- AffectedBlocks is a table full of cBlockToEntityData
    for n, k in pairs(AffectedBlocks) do
        if k:GetBlockType() == E_BLOCK_DIRT then
            table.remove(AffectedBlocks, n)
        end
    end
    -- send the modified table to the server to be processed
end