# Accessing Memcached from Exim

You can get [Exim](https://www.exim.org/) to set and get arbitrary values in
[memcached](https://memcached.org/) by using the
[${readsocket}](https://www.exim.org/exim-html-current/doc/html/spec_html/ch11.html)
string expansion.

I initially installed version 1.2.2 of memcached as that is the one that
currently comes as a Debian package with Lenny. I [found a
bug](https://code.google.com/p/memcached/issues/detail?id=49) in that version
however so had to upgrade to the latest version (currently 1.2.8).

First of all define some macros at the top of the Exim config:

```ini
MEMCACHED_HOST = localhost
MEMCACHED_PORT = 11211
```

You may want to change those if your memcache daemon is listening elsewhere. The
below two macros do all the magic and need adding beneath the above two macros,
and shouldn't need changing if you just want to do basic get/set:

```text
MEMCACHED_SET = ${sg{${readsocket{inet:MEMCACHED_HOST:MEMCACHED_PORT}{set $acl_c_memcache_key 0 $acl_c_memcache_timeout ${strlen:$acl_c_memcache_value}\r\n$acl_c_memcache_value\r\nquit\r\n}}}{\N\r\n$\N}{}} MEMCACHED_GET = ${sg{${readsocket{inet:MEMCACHED_HOST:MEMCACHED_PORT}{get $acl_c_memcache_key\r\n}{5s}{\n}}}{\N^(?:VALUE \S+ \d+ \d+\r\n(.*?)\r\n)?END\r\n$\N}{\$1}}
```

Now, if you want to store some data in memcached, you set three acl variables
and call the MEMCACHED_SET macro. In the following example, I store a key which
is the connecting ip address and a value which is the envelope sender, and I set
the value to expire after 60 seconds.

```text
warn set acl_c_memcache_key     = $sender_host_address
     set acl_c_memcache_value   = $sender_address
     set acl_c_memcache_timeout = 60
     condition                  = ${if eq{MEMCACHED_SET}{STORED}}
     logwrite                   = Stored data in memcached
```

To do a lookup on the data you set acl_c_memcache_key and then call
MEMCACHED_GET. Eg:

```text
warn set acl_c_memcache_key = $sender_host_address
     logwrite               = MemCached stored value = MEMCACHED_GET
```

If you want no timeout then set it to 0. If you want a timeout which is longer
than 30 days, it gets a little more complicated as you need to use seconds from
the epoch. Check out the Expiration section in the [memcached protocol
documentation](https://github.com/memcached/memcached/blob/master/doc/protocol.txt).