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controllers/nginx-third-party/lua/vendor/lua-resty-dns-cache/README.md

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+#lua-resty-dns-cache
+
+A wrapper for [lua-resty-dns](https://github.com/openresty/lua-resty-dns) to cache responses based on record TTLs.
+
+Uses [lua-resty-lrucache](https://github.com/openresty/lua-resty-lrucache) and [ngx.shared.DICT](https://github.com/openresty/lua-nginx-module#ngxshareddict) to provide a 2 level cache.
+
+Can repopulate cache in the background while returning stale answers.
+
+#Overview
+
+```lua
+  lua_shared_dict dns_cache 1m;
+
+  init_by_lua '
+      require("resty.dns.cache").init_cache(200)
+  ';
+
+    server {
+
+        listen 80;
+        server_name dns_cache;
+
+        location / {
+            content_by_lua '
+                local DNS_Cache = require("resty.dns.cache")
+                local dns = DNS_Cache.new({
+                        dict = "dns_cache",
+                        negative_ttl = 30,
+                        max_stale = 300,
+                        resolver  = {
+                            nameservers = {"123.123.123.123"}
+                        }
+                    })
+
+                local host = ngx.req.get_uri_args()["host"] or "www.google.com"
+
+                local answer, err, stale = dns:query(host)
+                if err then
+                    if stale then
+                        ngx.header["Warning"] = "110: Response is stale"
+                        answer = stale
+                        ngx.log(ngx.ERR, err)
+                    else
+                        ngx.status = 500
+                        ngx.say(err)
+                        return ngx.exit(ngx.status)
+                    end
+                end
+
+                local cjson = require "cjson"
+                ngx.say(cjson.encode(answer))
+            ';
+        }
+    }
+```
+
+#Methods
+### init_cache
+`syntax: ok, err = dns_cache.init_cache(max_items?)`
+
+Creates a global lrucache object for caching responses.
+
+Accepts an optional `max_items` argument, defaults to 200 entries.
+
+Calling this repeatedly will reset the LRU cache
+
+### initted
+`syntax: ok = dns_cache.initted()`
+
+Returns `true` if LRU Cache has been initialised
+
+### new
+`syntax: ok, err = dns_cache.new(opts)`
+
+Returns a new DNS cache instance. Returns `nil` and a string on error
+
+Accepts a table of options, if no shared dictionary is provided only lrucache is used.
+
+* `dict` - Name of the [ngx.shared.DICT](https://github.com/openresty/lua-nginx-module#ngxshareddict) to use for cache.
+* `resolver` - Table of options passed to [lua-resty-dns](https://github.com/openresty/lua-resty-dns#new). Defaults to using Google DNS.
+* `normalise_ttl` - Boolean. Reduces TTL in cached answers to account for cached time. Defaults to `true`.
+* `negative_ttl` - Time in seconds to cache negative / error responses. `nil` or `false` disables caching negative responses. Defaults to `false`
+* `minimise_ttl` - Boolean. Set cache TTL based on the shortest DNS TTL in all responses rather than the first response. Defaults to `false`
+* `max_stale` - Number of seconds past expiry to return stale content rather than querying. Stale hits will trigger a non-blocking background query to repopulate cache.
+
+
+### query
+`syntax: answers, err, stale = c:query(name, opts?)`
+
+Passes through to lua-resty-dns' [query](https://github.com/openresty/lua-resty-dns#query) method.
+
+Returns an extra `stale` variable containing stale data if a resolver cannot be contacted.
+
+### tcp_query
+`syntax: answers, err, stale = c:tcp_query(name, opts?)`
+
+Passes through to lua-resty-dns' [tcp_query](https://github.com/openresty/lua-resty-dns#tcp_query) method.
+
+Returns an extra `stale` variable containing stale data if a resolver cannot be contacted.
+
+### set_timeout
+`syntax: c:set_timeout(time)`
+
+Passes through to lua-resty-dns' [set_timeout](https://github.com/openresty/lua-resty-dns#set_timeout) method.
+
+## Constants
+lua-resty-dns' [constants](https://github.com/openresty/lua-resty-dns#constants) are accessible on the `resty.dns.cache` object too.
+
+## TODO
+ * Cap'n'proto serialisation
+