Database.Redis.Sentinel

Configuration of Sentinel hosts.

Interact with a Redis datastore. See runRedis for details.

Exception thrown by Database.Redis.Sentinel.

Context for normal command execution, outside of transactions. Use runRedis to run actions of this type.

In this context, each result is wrapped in an Either to account for the possibility of Redis returning an Error reply.

Deconstruct Redis constructor.

unRedis and reRedis can be used to define instances for arbitrary typeclasses.

WARNING! These functions are considered internal and no guarantee is given at this point that they will not break in future.

Reconstruct Redis constructor.

This class captures the following behaviour: In a context m, a command will return its result wrapped in a "container" of type f.

Please refer to the Command Type Signatures section of this page for more information.

Constructs a Connection pool to a Redis server designated by the given ConnectInfo, then tests if the server is actually there. Throws an exception if the connection to the Redis server can't be established.

Destroy all idle resources in the pool.

Memory bracket around connect and disconnect.

Memory bracket around checkedConnect and disconnect

Information for connnecting to a Redis server.

It is recommended to not use the ConnInfo data constructor directly. Instead use defaultConnectInfo and update it with record syntax. For example to connect to a password protected Redis server running on localhost and listening to the default port:

myConnectInfo :: ConnectInfo
myConnectInfo = defaultConnectInfo {connectAuth = Just "secret"}

Default information for connecting:

 connectHost           = "localhost"
 connectPort           = PortNumber 6379 -- Redis default port
 connectAuth           = Nothing         -- No password
 connectDatabase       = 0               -- SELECT database 0
 connectMaxConnections = 50              -- Up to 50 connections
 connectMaxIdleTime    = 30              -- Keep open for 30 seconds
 connectTimeout        = Nothing         -- Don't add timeout logic
 connectTLSParams      = Nothing         -- Do not use TLS

Parse a ConnectInfo from a URL

Username is ignored, path is used to specify the database:

>>> parseConnectInfo "redis://username:password@host:42/2"Right (ConnInfo {connectHost = "host", connectPort = PortNumber 42, connectAuth = Just "password", connectDatabase = 2, connectMaxConnections = 50, connectMaxIdleTime = 30s, connectTimeout = Nothing, connectTLSParams = Nothing})

>>> parseConnectInfo "redis://username:password@host:42/db"Left "Invalid port: db"

The scheme is validated, to prevent mixing up configurations:

>>> parseConnectInfo "postgres://"Left "Wrong scheme"

Beyond that, all values are optional. Omitted values are taken from defaultConnectInfo:

>>> parseConnectInfo "redis://"Right (ConnInfo {connectHost = "localhost", connectPort = PortNumber 6379, connectAuth = Nothing, connectDatabase = 0, connectMaxConnections = 50, connectMaxIdleTime = 30s, connectTimeout = Nothing, connectTLSParams = Nothing})

Constructs a ShardMap of connections to clustered nodes. The argument is a ConnectInfo for any node in the cluster

Some Redis commands are currently not supported in cluster mode - CONFIG, AUTH - SCAN - MOVE, SELECT - PUBLISH, SUBSCRIBE, PSUBSCRIBE, UNSUBSCRIBE, PUNSUBSCRIBE, RESET

Encapsulates subscription changes. Use subscribe, unsubscribe, psubscribe, punsubscribe or mempty to construct a value. Combine values by using the Monoid interface, i.e. mappend and mconcat.

sendRequest can be used to implement commands from experimental versions of Redis. An example of how to implement a command is given below.

-- |Redis DEBUG OBJECT command
debugObject :: ByteString -> Redis (Either Reply ByteString)
debugObject key = sendRequest ["DEBUG", "OBJECT", key]

Low-level representation of replies from the Redis server.

Compute the hashslot associated with a key

Options for the sort command.

Post a message to a channel (http://redis.io/commands/publish).

Listens to published messages on subscribed channels and channels matching the subscribed patterns. For documentation on the semantics of Redis Pub/Sub see http://redis.io/topics/pubsub.

The given callback function is called for each received message. Subscription changes are triggered by the returned PubSub. To keep subscriptions unchanged, the callback can return mempty.

Example: Subscribe to the "news" channel indefinitely.

 pubSub (subscribe ["news"]) $ \msg -> do
     putStrLn $ "Message from " ++ show (msgChannel msg)
     return mempty
 

Example: Receive a single message from the "chat" channel.

 pubSub (subscribe ["chat"]) $ \msg -> do
     putStrLn $ "Message from " ++ show (msgChannel msg)
     return $ unsubscribe ["chat"]
 

It should be noted that Redis Pub/Sub by its nature is asynchronous so returning unsubscribe does not mean that callback won't be able to receive any further messages. And to guarantee that you won't won't process messages after unsubscription and won't unsubscribe from the same channel more than once you need to use IORef or something similar

Listen for messages published to the given channels (http://redis.io/commands/subscribe).

Stop listening for messages posted to the given channels (http://redis.io/commands/unsubscribe).

Listen for messages published to channels matching the given patterns (http://redis.io/commands/psubscribe).

Stop listening for messages posted to channels matching the given patterns (http://redis.io/commands/punsubscribe).

Open a connection to the Redis server, register to all channels in the PubSubController, and process messages and subscription change requests forever. The only way this will ever exit is if there is an exception from the network code or an unhandled exception in a MessageCallback or PMessageCallback. For example, if the network connection to Redis dies, pubSubForever will throw a ConnectionLost. When such an exception is thrown, you can recall pubSubForever with the same PubSubController which will open a new connection and resubscribe to all the channels which are tracked in the PubSubController.

The general pattern is therefore during program startup create a PubSubController and fork a thread which calls pubSubForever in a loop (using an exponential backoff algorithm such as the retry package to not hammer the Redis server if it does die). For example,

myhandler :: ByteString -> IO ()
myhandler msg = putStrLn $ unpack $ decodeUtf8 msg

onInitialComplete :: IO ()
onInitialComplete = putStrLn "Redis acknowledged that mychannel is now subscribed"

main :: IO ()
main = do
  conn <- connect defaultConnectInfo
  pubSubCtrl <- newPubSubController [("mychannel", myhandler)] []
  concurrently ( forever $
      pubSubForever conn pubSubCtrl onInitialComplete
        `catch` (\(e :: SomeException) -> do
          putStrLn $ "Got error: " ++ show e
          threadDelay $ 50*1000) -- TODO: use exponential backoff
       ) $ restOfYourProgram


  {- elsewhere in your program, use pubSubCtrl to change subscriptions -}

At most one active pubSubForever can be running against a single PubSubController at any time. If two active calls to pubSubForever share a single PubSubController there will be deadlocks. If you do want to process messages using multiple connections to Redis, you can create more than one PubSubController. For example, create one PubSubController for each getNumCapabilities and then create a Haskell thread bound to each capability each calling pubSubForever in a loop. This will create one network connection per controller/capability and allow you to register separate channels and callbacks for each controller, spreading the load across the capabilities.

A Redis channel name

A Redis pattern channel name

A handler for a message from a subscribed channel. The callback is passed the message content.

Messages are processed synchronously in the receiving thread, so if the callback takes a long time it will block other callbacks and other messages from being received. If you need to move long-running work to a different thread, we suggest you use TBQueue with a reasonable bound, so that if messages are arriving faster than you can process them, you do eventually block.

If the callback throws an exception, the exception will be thrown from pubSubForever which will cause the entire Redis connection for all subscriptions to be closed. As long as you call pubSubForever in a loop you will reconnect to your subscribed channels, but you should probably add an exception handler to each callback to prevent this.

A handler for a message from a psubscribed channel. The callback is passed the channel the message was sent on plus the message content.

Similar to MessageCallback, callbacks are executed synchronously and any exceptions are rethrown from pubSubForever.

A controller that stores a set of channels, pattern channels, and callbacks. It allows you to manage Pub/Sub subscriptions and pattern subscriptions and alter them at any time throughout the life of your program. You should typically create the controller at the start of your program and then store it through the life of your program, using addChannels and removeChannels to update the current subscriptions.

Create a new PubSubController. Note that this does not subscribe to any channels, it just creates the controller. The subscriptions will happen once pubSubForever is called.

Get the list of current channels in the PubSubController. WARNING! This might not exactly reflect the subscribed channels in the Redis server, because there is a delay between adding or removing a channel in the PubSubController and when Redis receives and processes the subscription change request.

Get the list of current pattern channels in the PubSubController. WARNING! This might not exactly reflect the subscribed channels in the Redis server, because there is a delay between adding or removing a channel in the PubSubController and when Redis receives and processes the subscription change request.

Add channels into the PubSubController, and if there is an active pubSubForever, send the subscribe and psubscribe commands to Redis. The addChannels function is thread-safe. This function does not wait for Redis to acknowledge that the channels have actually been subscribed; use addChannelsAndWait for that.

You can subscribe to the same channel or pattern channel multiple times; the PubSubController keeps a list of callbacks and executes each callback in response to a message.

The return value is an action UnregisterCallbacksAction which will unregister the callbacks, which should typically used with bracket.

Call addChannels and then wait for Redis to acknowledge that the channels are actually subscribed.

Note that this function waits for all pending subscription change requests, so if you for example call addChannelsAndWait from multiple threads simultaneously, they all will wait for all pending subscription changes to be acknowledged by Redis (this is due to the fact that we just track the total number of pending change requests sent to Redis and just wait until that count reaches zero).

This also correctly waits if the network connection dies during the subscription change. Say that the network connection dies right after we send a subscription change to Redis. pubSubForever will throw ConnectionLost and addChannelsAndWait will continue to wait. Once you recall pubSubForever with the same PubSubController, pubSubForever will open a new connection, send subscription commands for all channels in the PubSubController (which include the ones we are waiting for), and wait for the responses from Redis. Only once we receive the response from Redis that it has subscribed to all channels in PubSubController will addChannelsAndWait unblock and return.

Remove channels from the PubSubController, and if there is an active pubSubForever, send the unsubscribe commands to Redis. Note that as soon as this function returns, no more callbacks will be executed even if more messages arrive during the period when we request to unsubscribe from the channel and Redis actually processes the unsubscribe request. This function is thread-safe.

If you remove all channels, the connection in pubSubForever to redis will stay open and waiting for any new channels from a call to addChannels. If you really want to close the connection, use killThread or Control.Concurrent.Async.cancel to kill the thread running pubSubForever.

Call removeChannels and then wait for all pending subscription change requests to be acknowledged by Redis. This uses the same waiting logic as addChannelsAndWait. Since removeChannels immediately notifies the PubSubController to start discarding messages, you likely don't need this function and can just use removeChannels.

An action that when executed will unregister the callbacks. It is returned from addChannels or addChannelsAndWait and typically you would use it in bracket to guarantee that you unsubscribe from channels. For example, if you are using websockets to distribute messages to clients, you could use something such as:

websocketConn <- Network.WebSockets.acceptRequest pending
let mycallback msg = Network.WebSockets.sendTextData websocketConn msg
bracket (addChannelsAndWait ctrl [("hello", mycallback)] []) id $ const $ do
  {- loop here calling Network.WebSockets.receiveData -}

Watch the given keys to determine execution of the MULTI/EXEC block (http://redis.io/commands/watch).

Forget about all watched keys (http://redis.io/commands/unwatch).

Run commands inside a transaction. For documentation on the semantics of Redis transaction see http://redis.io/topics/transactions.

Inside the transaction block, command functions return their result wrapped in a Queued. The Queued result is a proxy object for the actual command's result, which will only be available after EXECing the transaction.

Example usage (note how Queued 's Applicative instance is used to combine the two individual results):

 runRedis conn $ do
     set "hello" "hello"
     set "world" "world"
     helloworld <- multiExec $ do
         hello <- get "hello"
         world <- get "world"
         return $ (,) <$> hello <*> world
     liftIO (print helloworld)
 

A Queued value represents the result of a command inside a transaction. It is a proxy object for the actual result, which will only be available after returning from a multiExec transaction.

Queued values are composable by utilizing the Functor, Applicative or Monad interfaces.

Result of a multiExec transaction.

Command-context inside of MULTI/EXEC transactions. Use multiExec to run actions of this type.

In the RedisTx context, all commands return a Queued value. It is a proxy object for the actual result, which will only be available after finishing the transaction.

Options for the migrate command.

Redis default MigrateOpts. Equivalent to omitting all optional parameters.

MigrateOpts
    { migrateCopy    = False -- remove the key from the local instance
    , migrateReplace = False -- don't replace existing key on the remote instance
    }

Redis default ScanOpts. Equivalent to omitting all optional parameters.

ScanOpts
    { scanMatch = Nothing -- don't match any pattern
    , scanCount = Nothing -- don't set any requirements on number elements returned (works like value COUNT 10)
    }

Redis default SortOpts. Equivalent to omitting all optional parameters.

SortOpts
    { sortBy    = Nothing -- omit the BY option
    , sortLimit = (0,-1)  -- return entire collection
    , sortGet   = []      -- omit the GET option
    , sortOrder = Asc     -- sort in ascending order
    , sortAlpha = False   -- sort numerically, not lexicographically
    }

Works like eval, but sends the SHA1 hash of the script instead of the script itself. Fails if the server does not recognise the hash, in which case, eval should be used instead.

A single entry from the slowlog.

Redis default ZaddOpts. Equivalent to omitting all optional parameters.

ZaddOpts
    { zaddCondition = Nothing -- omit NX and XX options
    , zaddChange    = False   -- don't modify the return value from the number of new elements added, to the total number of elements changed
    , zaddIncrement = False   -- don't add like ZINCRBY
    }