view mod_storage_multi/mod_storage_multi.lua @ 5551:8bfcedd93a72

mod_rest: List all error conditions in OpenAPI spec These are not handled by datamanager but by util.stanza and util.error, so they are not represented in the JSON schema file.
author Kim Alvefur <zash@zash.se>
date Sat, 17 Jun 2023 16:26:33 +0200
parents 8c4a2d85e8bf
children
line wrap: on
line source

-- mod_storage_multi

local storagemanager = require"core.storagemanager";
local backends = module:get_option_array(module.name); -- TODO better name?

-- TODO migrate data "upwards"

-- one → one successful write is success
-- all → all backends must report success
-- majority → majority of backends must report success
local policy = module:get_option_string(module.name.."_policy", "all");

local keyval_store = {};
keyval_store.__index = keyval_store;

function keyval_store:get(username)
	local backends = self.backends;
	local data, err;
	for i = 1, #backends do
		module:log("debug", "%s:%s:get(%q)", tostring(backends[i].get), backends[i]._store, username);
		data, err = backends[i]:get(username);
		if err then
			module:log("error", tostring(err));
		elseif not data then
			module:log("debug", "No data returned");
		else
			module:log("debug", "Data returned");
			return data, err;
		end
	end
end

-- This is where it gets complicated
function keyval_store:set(username, data)
	local backends = self.backends;
	local ok, err, backend;
	local all, one, oks = true, false, 0;
	for i = 1, #backends do
		backend = backends[i];
		module:log("debug", "%s:%s:set(%q)", tostring(backends[i].get), backends[i].store, username);
		ok, err = backend:set(username, data);
		if not ok then
			module:log("error", "Error in storage driver %s: %s", backend.name, tostring(err));
		else
			oks = oks + 1;
		end
		one = one or ok; -- At least one successful write
		all = all and ok; -- All successful
	end
	if policy == "all" then
		return all, err
	elseif policy == "majority" then
		return oks > (#backends/2), err;
	end
	-- elseif policy == "one" then
	return one, err;
end

local stores = {
	keyval = keyval_store;
}

local driver = {};

function driver:open(store, typ)
	local store_mt = stores[typ or "keyval"];
	if store_mt then
		local my_backends = {};
		local driver, opened
		for i = 1, #backends do
			 driver = storagemanager.load_driver(module.host, backends[i]);
			 opened = driver:open(store, typ);
			 my_backends[i] = assert(driver:open(store, typ));
			 my_backends[i]._store = store;
		end
		return setmetatable({ backends = my_backends }, store_mt);
	end
	return nil, "unsupported-store";
end

module:provides("storage", driver);