# libr3

### what's libr3?
[libr3](https://github.com/c9s/r3) is a high-performance path dispatching library. It compiles your route paths into a prefix tree (trie).

APISIX using [lua-resty-libr3](https://github.com/iresty/lua-resty-libr3) as route dispatching library.

### How to use libr3 in APISIX?
libr3 supports PCRE(Perl Compatible Regular Expressions), so you can use route flexibly.

Let's take a look at a few examples and have an intuitive understanding.

1. default regular expression

`/blog/post/{id}`

there is not regular expression included, and `[^/]+` will be the default
regular expression of `id`.

So `/blog/post/{id}` is equivalent to `/blog/post/{id:[^/]+}`.

2. match all uris

`/{:.*}`

`/` matches root uri, and `.*` matches any character (except for line terminators).

`:` means is an anonymous match, for example the uri is `/blog/post/1`, the libr3 will return `[/blog/post/1]` if pattern is `/{:.*}`, and return `{"uri":"/blog/post/1"}` if pattern is `/{uri:.*}`.

3. match number

`/blog/post/{id:\d+}`

for example the uri is `/blog/post/1`, libr3 will return `{"id":"1"}`.

4. match characters

`/blog/post/{name:\w+}`

for example the uri is `/blog/post/foo`, libr3 will return `{"name":"foo"}`.

5. match multiple uri segments

`/blog/post/{name:\w+}/{id:\d+}`

for example the uri is `/blog/post/foo/12`, libr3 will return `{"name":"foo", "id":"12"}`.

`/blog/post/{:\w+}/{id:\d+}`

for example the uri is `/blog/post/foo/12`, libr3 will return `{"1":"foo", "id":"12"}`.

### How to filter route by Nginx builtin variable

Please take a look at [radixtree-new](https://github.com/iresty/lua-resty-radixtree#new),
here is an example:

```shell
$ curl http://127.0.0.1:9080/apisix/admin/routes/1 -X PUT -i -d '
{
    "uri": "/index.html",
    "vars": ["http_k", "header", "cookie_k", "cookie", "arg_k", "uri_arg"],
    "upstream": {
        "type": "roundrobin",
        "nodes": {
            "39.97.63.215:80": 1
        }
    }
}'
```

This route will require the request header `k` equal "header", request cookie key `k` equal "cookie" etc.