Network.Starling

A haskell implementation of the memcahed protocol.

This implements the new binary protocol, so it only works with memcached version 1.3 and newer.

Example of usage, using the network package to obain a handle, and the OverloadedStrings language extension:

 h <- connectTo "filename" $ UnixSocket "filename"
 hSetBuffering h NoBuffering
 con <- open h

 set con "hello" "world"
 get con "hello"

In the above example we connect to a unix socket in the file "filename", set the key "hello" to the value "world" and then retrieve the value.

Operations are thread safe - multiple threads of execution may make concurrent requests on the memcahced connection.

Operations are blocking, but do not block other concurrent threads from placing requests on the connection.

Documentation

open :: Handle -> IO Connection

Create a connection. Please don't use the handle after opening a connection with it.

close :: Connection -> IO ()

Shut down the connection. Non-blocking.

data Connection

For thread safety of operations, we perform all requests on a wrapper around a handle.

type Key = ByteString

type Value = ByteString

type Result a = ResultM IO a

type ResultM m a = m (Either (ResponseStatus, ByteString) a)

If an operation fails the result will return in Left with the failure code and a text description of the failure

data ResponseStatus

Constructors

NoError

KeyNotFound

KeyExists

ValueTooLarge

InvalidArguments

ItemNotStored

IncrDecrOnNonNumeric

UnknownCommand

OutOfMemory

Instances

Eq ResponseStatus

Ord ResponseStatus

Read ResponseStatus

Show ResponseStatus

Deserialize ResponseStatus

set :: Connection -> Key -> Value -> Result ()

Set a value in the cache

get :: Connection -> Key -> Result ByteString

Retrive a value from the cache

delete :: Connection -> Key -> Result ()

Delete an entry in the cache

add :: Connection -> Key -> Value -> Result ()

Set a vlue in the cache. Fails if a value is already defined for the indicated key.

replace :: Connection -> Key -> Value -> Result ()

Set a value in the cache. Fails if a value is not already defined for the indicated key.

update :: MonadIO m => Connection -> Key -> (Value -> m (Maybe Value)) -> ResultM m ()

Update a value in the cache. This operation requires two round trips. This operation can fail if the key is not present in the cache, or if the value changes in the cache between the two calls. So watch out! Even if the value exists the operation might not go through in the face of concurrent access.

Testing indicates that if we fail because we could not gaurantee atomicity the failure code will be KeyExists.

increment :: Connection -> Key -> Word64 -> Word64 -> Result Word64

Increment a value in the cache. The first Word64 argument is the amount by which to increment and the second is the intial value to use if the key does not yet have a value. The return value is the updated value in the cache.

decrement :: Connection -> Key -> Word64 -> Word64 -> Result Word64

Decrement a value in the cache. The first Word64 argument is the amount by which to decrement and the second is the intial value to use if the key does not yet have a value. The return value is the updated value in the cache.

flush :: Connection -> Result ()

Delete all entries in the cache

stats :: Connection -> Result [(ByteString, ByteString)]

Returns a list of stats about the server in key,value pairs

version :: Connection -> Result ByteString

Returns the version of the server