util/memcache.lua

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local now = os.time;

module("memcache", package.seeall);

local max_expires_seconds = 60*60*24*30;

function new()
	local cache = {};
	
	local _data = {};
	local _flags = {};
	local _expiry = {};
	local _deleted = {};
	
	function cache:set(key, flags, expires, data)
		_flags[key] = flags;
		if expires > 0 then
			if expires <= max_expires_seconds then
				expires = now() + expires;
			end
			_expiry[key] = expires;
		end
		_deleted[key] = nil;
		_data[key] = data;
		return true, true;
	end
	
	function cache:add(key, flags, expires, data)
		if not(_data[key]) and (not(_deleted[key]) or _deleted[key] < now()) then
			return self:set(key, flags, expires, data);
		end
		return true, false; -- No error, but data was not stored
	end
	
	function cache:replace(key, flags, expires, data)
		if _data[key] and (not(_deleted[key]) or _deleted[key] < now()) then
			return self:set(key, flags, expires, data);
		end
		return true, false; -- No error, but data was not stored
	end
	
	function cache:exists(key)
		return not not _data[key];
	end
	
	function cache:get(key)
		local expires = _expiry[key];
		if expires and expires < now() then
			self:delete(key);
		end
		return _flags[key], tostring(_data[key]);
	end
	
	function cache:delete(key, time)
		local existed = _data[key];
		_flags[key], _data[key], _expiry[key] = nil, nil, nil;
		if existed and time then
			if time <= max_expires_seconds then
				time = now() + time;
			end
			_deleted[key] = time;
		end
		return true, existed;
	end
	
	function cache:incr(key, amount)
		local current_value = tonumber((select(2, self:get(key)))) or 0;
		local new_value = (current_value + amount)%4294967296;
		local ok, err = cache:set(key, 0, 0, new_value);
		if not ok then
			return ok, err;
		end
		return ok, new_value;
	end
	
	function cache:decr(key, amount)
		local current_value = tonumber((select(2, self:get(key)))) or 0;
		local new_value = math.max(0, current_value - amount);
		local ok, err = cache:set(key, 0, 0, new_value);
		if not ok then
			return ok, err;
		end
		return ok, new_value;
	end
	
	return cache;
end

return _M;