Add README

README.md

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+#lua-resty-tlc
+
+Two Layer Cache implementation using [lua-resty-lrucache](https://github.com/openresty/lua-resty-lrucache) and [shared dictionaries](https://github.com/openresty/lua-nginx-module#ngxshareddict).
+
+Cache entries are written to lru-cache in the current worker and to a shared dictionary.
+
+Cache reads that miss in the worker's lru-cache instance are re-populated from the shared dictionary if available.
+
+Values in shared dictionaries are automatically serialised and unserialised to JSON (custom serialisation functions are supported)
+
+Also provides a manager module to maintain global set of TLC cache instances
+
+#Overview
+
+```lua
+lua_package_path "/path/to/lua-resty-tlc/lib/?.lua;;";
+
+lua_shared_dict tlc_cache 10m;
+lua_shared_dict tlc_cache2 1m;
+
+init_by_lua_block {
+    local manager = require("resty.tlc.manager")
+    manager.new("my_cache", {size = 500, dict = "tlc_cache"})
+
+    manager.new("my_cache2", {size = 500, dict = "tlc_cache2"})
+}
+
+
+location = /get {
+    content_by_lua_block {
+        local manager = require("resty.tlc.manager")
+        local cache = manager.get("my_cache")
+
+        local args = ngx.req.get_uri_args()
+        local key = args["key"]
+
+        local data, err = cache:get(key)
+        if err then
+            ngx.log(ngx.ERR, err)
+        elseif data == nil then
+            ngx.status = ngx.HTTP_NOT_FOUND
+            ngx.say("Not Found")
+        else
+            ngx.say(tostring(data))
+        end
+    }
+}
+
+location = /set {
+    content_by_lua_block {
+        local manager = require("resty.tlc.manager")
+        local cache = manager.get("my_cache")
+
+        local args = ngx.req.get_uri_args()
+        local key = args["key"]
+        local val = args["val"] or { foo = bar }
+        local ttl = args["ttl"]
+
+        local ok, err = cache:set(key, val, ttl)
+        if not ok then
+            ngx.log(ngx.ERR, err)
+        end
+    }
+}
+
+location = /flush {
+    content_by_lua_block {
+        local manager = require("resty.tlc.manager")
+        local cache = manager.get("my_cache")
+        cache:flush()
+    }
+}
+
+location = /list {
+    content_by_lua_block {
+        local manager = require("resty.tlc.manager")
+        local instances = manager.list()
+
+        ngx.say(require("cjson").encode(instances))
+    }
+}
+
+
+```
+
+#Methods
+
+* [manager](#manager)
+ * [new](#new)
+ * [get](#get)
+ * [set](#set)
+ * [delete](#delete)
+ * [list](#list)
+* [cache](#cache)
+ * [new](#new-1)
+ * [set](#set-1)
+ * [get](#get-1)
+ * [delete](#delete-1)
+ * [flush](#flush)
+
+## manager
+
+### new
+`syntax: ok, err = manager.new(name, opts)`
+
+Create a new `resty.tlc.cache` instance with given name/id and options.
+
+Will **not** check if instance already exists, existing instances will be overwritten
+
+### get
+`syntax: cache = manager.get(name)`
+
+Returns the specified TLC cache instance or nil
+
+### delete
+`syntax: manager.delete(name)`
+
+Removes the specified cache instance.
+
+### list
+`syntax: instances = manager.list()`
+
+Returns an array table of available cache instances
+
+## cache
+
+### new
+`syntax: instance = cache:new(opts)`
+
+Creates a new instance of `resty.tlc.cache`, `opts` is a table of options for this instance.
+
+```lua
+opts = {
+    dict         = dict,         -- Shared dictionary name, required
+    size         = size,         -- max_items parameter for LRU cache, optional, default 200
+    pureffi      = pureffi,      -- Use the pureffi LRU cache variant, optional, default false
+    loadfactor   = loadfactor,   -- Load factor for pureffi LRU cache, optional
+    serialiser   = serialiser,   -- Function to serialise values when saving to shared dictionary, optional, defaults to pcall'd cjson encode
+    unserialiser = unserialiser, -- Function to unserialise values when saving to shared dictionary, optional, defaults to pcall'd cjson decode
+}
+```
+
+Functions to serialise and unserialise should `return nil, err` on failure.
+
+### set
+`syntax: ok, err = cache:set(key, value, ttl?)`
+
+Set or update an entry in the cache.
+
+`ttl` is optional and in seconds
+
+
+### get
+`syntax: data = cache:get(key)`
+
+Returns data from cache or `nil` if not set
+
+
+### delete
+`syntax: cache:delete(key)`
+
+Deletes entry from both LRU cache and shared dictionary
+
+TODO: Delete from LRU cache in all workers
+
+### flush
+`syntax: cache:flush(hard?)`
+
+Re-initialises LRU cache in current worker and flushes shared dictionary.
+
+`hard` argument will also call `flush_expired()` on dictionary.
+
+TODO: Re-initialise LRU cache in all workers
+
+
+# TODO
+
+* Add feature to ngx_lua shared dictionary to retrieve remaining TTL of entry
+* Syncronise LRU cache delete / flush across workers
+