Redis

A simple Redis library providing high level access to Redis features we use here at NoRedInk

As with our Ruby Redis access, we enforce working within a "namespace".

Creating a redis handler

handler :: Text -> Settings -> Acquire Handler

Produce a namespaced handler for Redis access.

handlerAutoExtendExpire :: Text -> Settings -> Acquire HandlerAutoExtendExpire

Produce a namespaced handler for Redis access. This will ensure that we extend all keys accessed by a query by a configured default time (see Settings.defaultExpiry)

type Handler = Handler' 'NoAutoExtendExpire

This is a type alias of a handler parametrized by a value that indicates that the auto extend feature is disabled. Note: The tick in front of NoAutoExtendExpire is not necessary, but good practice to indicate that we are lifting a value to the type level.

type HandlerAutoExtendExpire = Handler' 'AutoExtendExpire

This is a type alias of a handler parametrized by a value that indicates that the auto extend feature is enabled. Note: The tick in front of AutoExtendExpire is not necessary, but good practice to indicate that we are lifting a value to the type level.

data Handler' (x :: HasAutoExtendExpire)

The redis handler allows applications to run scoped IO A handler that can only be parametrized by a value of this kind. Meaning that we use the values of the type parameter at a type level.

data HasAutoExtendExpire

We use this to parametrize the handler. It specifies if the handler has the auto extend expire feater enabled or not.

Constructors

NoAutoExtendExpire

AutoExtendExpire

data Settings

Settings required to initiate a redis connection.

Constructors

Settings

Fields

• connectionInfo :: ConnectInfo

  Full redis connection string.

  Default env var name is REDIS_CONNECTION_STRING default is "redis://localhost:6379"

• clusterMode :: ClusterMode

  Set to 1 for cluster, everything else is not.

  Default env var name is REDIS_CLUSTER Default is 0

• defaultExpiry :: DefaultExpiry

  Set a default amount of seconds after which all keys touched by this handler will expire. The expire time of a key is reset every time it is read or written. A value of 0 means no default expiry.

  Default env var name is REDIS_DEFAULT_EXPIRY_SECONDS default is 0

• queryTimeout :: QueryTimeout

  0 means no timeout, every other value is a timeout in milliseconds.

  Default env var name is REDIS_QUERY_TIMEOUT_MILLISECONDS default is 1000

• maxKeySize :: MaxKeySize

Instances

Show Settings

Defined in Redis.Settings

Methods

showsPrec :: Int -> Settings -> ShowS

show :: Settings -> String

showList :: [Settings] -> ShowS

decoder :: Decoder Settings

decodes Settings from environmental variables

decoderWithEnvVarPrefix :: Text -> Decoder Settings

decodes Settings from environmental variables prefixed with a Text >>> decoderWithEnvVarPrefix WORKER_

decoderWithCustomConnectionString :: Text -> Decoder Settings

decodes Settings from environmental variables with custom connection string

withQueryTimeoutMilliseconds :: Int -> Handler' x -> Task () (Handler' x)

Sets a timeout for the query in milliseconds.

withoutQueryTimeout :: Handler' x -> Task () (Handler' x)

Disables timeout for query in milliseconds

Creating a redis API

jsonApi :: forall a key. (ToJSON a, FromJSON a) => (key -> Text) -> Api key a

Creates a json API mapping a key to a json-encodable-decodable type

data Key = Key { fieldA: Text, fieldB: Text }
data Val = Val { ... }

myJsonApi :: Redis.Api Key Val
myJsonApi = Redis.jsonApi (\Key {fieldA, fieldB}-> Text.join "-" [fieldA, fieldB, "v1"])

textApi :: (key -> Text) -> Api key Text

Creates a Redis API mapping a key to Text

byteStringApi :: (key -> Text) -> Api key ByteString

Creates a Redis API mapping a key to a ByteString

data Api key a

a API type can be used to enforce a mapping of keys to values. without an API type, it can be easy to naiively serialize the wrong type into a redis key.

Out of the box, we have helpers to support - jsonApi for json-encodable and decodable values - textApi for Text values - byteStringApi for ByteString values

Creating redis queries

del :: Api key a -> NonEmpty key -> Query Int

Removes the specified keys. A key is ignored if it does not exist.

https://redis.io/commands/del

exists :: Api key a -> key -> Query Bool

Returns if key exists.

https://redis.io/commands/exists

expire :: Api key a -> key -> Int -> Query ()

Set a timeout on key. After the timeout has expired, the key will automatically be deleted. A key with an associated timeout is often said to be volatile in Redis terminology.

https://redis.io/commands/expire

get :: Api key a -> key -> Query (Maybe a)

Get the value of key. If the key does not exist the special value Nothing is returned. An error is returned if the value stored at key is not a string, because GET only handles string values.

https://redis.io/commands/get

getset :: Api key a -> key -> a -> Query (Maybe a)

Atomically sets key to value and returns the old value stored at key. Returns an error when key exists but does not hold a string value.

https://redis.io/commands/getset

mget :: Api key a -> Ord key => NonEmpty key -> Query (Dict key a)

Returns the values of all specified keys. For every key that does not hold a string value or does not exist, no value is returned. Because of this, the operation never fails.

https://redis.io/commands/mget

mset :: Api key a -> NonEmptyDict key a -> Query ()

Sets the given keys to their respective values. MSET replaces existing values with new values, just as regular SET. See MSETNX if you don't want to overwrite existing values.

MSET is atomic, so all given keys are set at once. It is not possible for clients to see that some of the keys were updated while others are unchanged.

https://redis.io/commands/mset

ping :: Api key a -> Query ()

Returns PONG if no argument is provided, otherwise return a copy of the argument as a bulk. This command is often used to test if a connection is still alive, or to measure latency.

https://redis.io/commands/ping

set :: Api key a -> key -> a -> Query ()

Set key to hold the string value. If key already holds a value, it is overwritten, regardless of its type. Any previous time to live associated with the key is discarded on successful SET operation.

https://redis.io/commands/set

setex :: Api key a -> key -> Int -> a -> Query ()

Set key to hold the string value and set key to timeout after a given number of seconds.

https://redis.io/commands/setex

setnx :: Api key a -> key -> a -> Query Bool

Set key to hold string value if key does not exist. In that case, it is equal to SET. When key already holds a value, no operation is performed. SETNX is short for "SET if Not eXists".

https://redis.io/commands/setnx

Running Redis queries

query :: HasCallStack => Handler' x -> Query a -> Task Error a

Run a Query. Note: A Query in this library can consist of one or more queries in sequence. if a Query contains multiple queries, it may make more sense, if possible to run them using transaction

transaction :: HasCallStack => Handler' x -> Query a -> Task Error a

Run a redis Query in a transaction. If the query contains several Redis commands they're all executed together, and Redis will guarantee other requests won't be able change values in between.

In redis terms, this is wrappping the Query in MULTI and `EXEC see redis transaction semantics here: https://redis.io/topics/transactions

data Query a

A Redis query

Instances

Functor Query

Defined in Redis.Internal

Methods

fmap :: (a -> b) -> Query a -> Query b

(<$) :: a -> Query b -> Query a

Show (Query a)

Defined in Redis.Internal

Methods

showsPrec :: Int -> Query a -> ShowS

show :: Query a -> String

showList :: [Query a] -> ShowS

data Error

Redis Errors, scoped by where they originate.

Constructors

RedisError Text

ConnectionLost

DecodingError Text

DecodingFieldError Text

LibraryError Text

TransactionAborted

TimeoutError

KeyExceedsMaxSize Text Int

Instances

ToJSON Error

Defined in Redis.Internal

Methods

toJSON :: Error -> Value

toEncoding :: Error -> Encoding

toJSONList :: [Error] -> Value

toEncodingList :: [Error] -> Encoding

Show Error

Defined in Redis.Internal

Methods

showsPrec :: Int -> Error -> ShowS

show :: Error -> String

showList :: [Error] -> ShowS

map :: (a -> b) -> Query a -> Query b

Used to map the type of a query to another type useful in combination with transaction

map2 :: (a -> b -> c) -> Query a -> Query b -> Query c

Used to combine two queries Useful to combine two queries. Redis.map2 (Maybe.map2 (,)) (Redis.get api1 key) (Redis.get api2 key) |> Redis.query redis

map3 :: (a -> b -> c -> d) -> Query a -> Query b -> Query c -> Query d

Used to combine three queries Useful to combine three queries.

sequence :: List (Query a) -> Query (List a)

Used to run a series of queries in sequence. Useful to run a list of queries in sequence. queries |> Redis.sequence |> Redis.query redis

foldWithScan :: Handler' x -> Maybe Text -> Maybe Int -> ([Text] -> a -> Task Error a) -> a -> Task Error a

Use SCAN command to find keys matching a pattern, and "fold" over them in batches, producing a result value. keyMatchPattern A glob-like pattern to match keys, see https://redis.io/commands/keys/ approxCountPerBatch A hint for the batch size you want to process at once. Only approximate. processKeyBatch Function to process one batch of keys (provided as plain Text without namespace prefix) initAccumulator Initial value for the fold accumulator

Lua Scripting

script :: QuasiQuoter

Quasi-quoter for creating a Redis Lua script with placeholders for Redis keys and arguments.

[script|SET ${Key "a-redis-key"} ${Literal 123}|]

• *IMPORTANT**: It is NOT SAFE to return Redis keys using this. Our Redis APIs inject "namespaces" (prefixes) on keys, and any keys returned by Lua will have their namespaces applied. If you try to reuse those keys in follow-up queries, namespaces will be doubly-applied.

data ScriptParam

A type for enforcing parameters used in [script|${ ... }|] are either tagged as Key or Literal.

We need keys to be tagged, otherwise we can't implement mapKeys and enforce namespacing in Redis APIs.

We make this extra generic to allow us to provide nice error messages using TypeError in a type class below.

Constructors

forall a.Show a => Key a

forall a.Show a => Literal a

eval :: (HasCallStack, RedisResult a) => Handler' x -> Script a -> Task Error a