BSD-3-Clause licensed by Yorick Laupa
Maintained by [email protected]
This version can be pinned in stack with:eventstore-1.3.3@sha256:3cdb84742dc00a5305e9192ed6e183fb03d0cf2ea40c575d4c0b9980984c5f8f,5778

Module documentation for 1.3.3

EventStore Haskell TCP client

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That driver supports 100% of EventStore features ! More information about the GetEventStore database can be found there:


  • 64bits system
  • GHC >= 8.0.3
  • Cabal >= 1.18
  • EventStore >= 4

Note: If you use this client version >= to 1.1, it will only supports EventStore >= 4.0.0.


$ cabal update
$ cabal install eventstore
  • From source
$ git clone
$ cd eventstore
$ cabal install --only-dependencies
$ cabal configure
$ cabal install

How to test

Tests are available. Those assume a server is running on and 1113 port.

$ cabal install --only-dependencies --enable-tests
$ cabal configure --enable-tests
$ cabal test

How to use

{-# LANGUAGE OverloadedStrings #-} -- That library uses `Text` pervasively. This pragma permits to use
                                   -- String literal when a Text is needed.
module Main where

import Control.Concurrent.Async (wait)
import Data.Aeson
-- It requires to have `aeson` package installed. Note that EventStore doesn't constraint you to JSON
-- format but putting common use aside, by doing so you'll be able to use some interesting EventStore
-- features like its Complex Event Processing (CEP) capabality.

import Database.EventStore
-- Note that imports 'NonEmpty' data constructor and 'nonEmpty' function from
-- 'Data.List.NonEmpty'.

main :: IO ()
main = do
    -- A common pattern with an EventStore connection is to create a single instance only and pass it
    -- wherever you need it (it's threadsafe). It's very important to not consider an EventStore connection like
    -- its regular SQL counterpart. An EventStore connection will try its best to reconnect
    -- automatically to the server if the connection dropped. Of course that behavior can be tuned
    -- through some settings.
    conn <- connect defaultSettings (Static "" 1113)
    let js  = object ["isHaskellTheBest" .= True] -- (.=) comes from Data.Aeson module.
        evt = createEvent "programming" Nothing (withJson js)

    -- Appends an event to a stream named `languages`.
    as <- sendEvent conn (StreamName "languages") anyVersion evt Nothing

    -- EventStore interactions are fundamentally asynchronous. Nothing requires you to wait
    -- for the completion of an operation, but it's good to know if something went wrong.
    _ <- wait as

    -- Again, if you decide to `shutdown` an EventStore connection, it means your application is
    -- about to terminate.
    shutdown conn

    -- Make sure the EventStore connection completes every ongoing operation. For instance, if
    -- at the moment we call `shutdown` and some operations (or subscriptions) were still pending,
    -- the connection aborted all of them.
    waitTillClosed conn


That library was tested on Linux and OSX.

Contributions and bug reports are welcome!

BSD3 License

-Yorick Laupa



  • Add Pinned system consumer strategy.


  • Bug fix: Driver could end in a situation where it receives a close-connection message during Authentication/Identification phase. Close-connection message was wrongly ignored letting pending operations unanwsered at call-site. If the user forced the result of an operation, it could have lead the current thread to block indefinately. The client state-machine switched to a wrong state.


  • Better encoding of streaming interface ReadError.
  • Expose more internal functions of the streaming interface.
  • Internal: Reset heartbeat tracking on force reconnect request.
  • Bug fix: Increment package number unless connection is init or closed (prevent false heartbeat timeout).
  • Bug fix: Was also using s_heartbeatInterval value for s_heartbeatTimeout causing false heartbeat timeout exceptions.
  • Bug fix: Stop trying to reconnect to the most recent node that failed (cluster connection mode).


  • Discard machines dependency.
  • Remove connection upper bound version.


  • Fix possible connection issues if Authentication or Identification processes takes too long to complete.


  • No longer terminate the connection in case of IdentificationTimeout.


  • Fix ACL JSON (de)serialization.
  • Fix rare situation where the user send a command before the connection with the server is available, causing that operation to be sent only after s_operationTimeout milliseconds.
  • Fix “thread blocked indefinitely in an STM transaction” error when failed to create a connection with the server and exceeded the maximun attempt count.
  • Fix: Cluster connection, in the discovery process using gossip seed, we try for the next seed if the current one is unreachable.


  • Bump http-client version.


  • Introduce a type-safe EventNumber setting.
  • Introduce a type-safe ResolveLink setting.
  • Support GHC 8.6 but drop GHC < 8.
  • Refactor Slice api.
  • Implement a stream-processing interface.
  • typeful stream id representation.
  • Uniform batch-read and subscription interface.


  • Update package metadata information.


  • Bump aeson version.


  • Fix compilation on GHC 8.4


  • Remove text-format dependency.


  • Aeson bump version.


  • Fix connection-manager connection reference. The issue was the client was starting to send requests to server even if the confirmation hasn’t been confirmed yet.


  • Supports GetEventStore >= 4.0.0 protocol changes.
  • No longer support GetEventStore < 4.0.0.
  • Stream versions are Int64.


  • Support SemVer versioning.

  • Support GHC 8.2.1.
  • Support Stackage LTS 9.

  • Discard version restriction on hashable library.

  • Overall internal components refactoring.
  • Decrease memory pressure by 10 folds.
  • Improve general performance.
  • Provide proper logging support using fast-logger library.
  • Support operation timeout detection.
  • Detects if the server is overwhelmed and act accordingly.
  • Improve connection management code.
  • Expose EKG monitoring metrics.

  • Fix subscription deadlock on connection drop.
  • Fix subscription catchup state tracking on connection drop.
  • Fix internal connection dispose lock implementation.
  • Bump aeson version.

  • Fix deadlock issues in subscription code.
  • Improve cluster connection fiability.
  • Internal refactoring.
  • Typeful EventType

  • Report stream name when facing a ‘Stream not found’ error from the server on catchup subscription.
  • Prevent the driver from deadlocking when asking for catchup subscription on a stream that doesn’t exist.

  • Fix a deadlock on user side when asking a catchup subscription on a stream that doesn’t exist.

  • Fix an internal connection bug.

  • Bump aeson version.
  • Internal connection refactoring.

  • Bump http-client version.

  • Restrain http-client package version.

  • Typo on streamExists implementation.

  • Add streamExists ExpectedVersion smart constructor.

  • Bump protobuf version

  • Implement SSL Connection
  • Implement waitConfirmation function

  • Quit using internal .NET TimeSpan for dotnet-timespan TimeSpan

  • Implement Cluster connection.
  • Domain can be used to connect to a server instance.

  • Bump aeson version.

  • Bump async version.

  • Fix $maxAge and $cacheControl TimeSpan metadata serialization.
  • Fix timeSpanFrom* functions.
  • Implement timeSpanTotalDays, timeSpanTotalHours, timeSpanTotalMinutes and timeSpanTotalSeconds.
  • Add withBinary and withBinaryAndMetadata.
  • Remove useless TimeSpan ToJSON and FromJSON instances.
  • Drop attoparsec dependency.

  • Increase cereal upper bound to <0.6

  • Increase aeson upper bound to <0.11

  • Fix stackage integration.

  • Introduce convinient persistent subscription functions.
  • Add multi GHC version testing.

  • Rewrite entirely the internals.
  • Implement integration tests.
  • Rename every ExpectedVersion smart constructors.
  • Improve internal and public documentation.
  • Improve failure reports when the connection dropped.
  • Implement more robust internal connection.

  • Implement competing consumers.
  • Expose an uniform API among all kind of subscriptions.
  • Rewrite internal subscription management.
  • Add missing Eq or Show instances for exposed datatypes.
  • Add streamMetadataCustomPropertyValue and streamMetadataCustomProperty.
  • Add logging capability.

  • Fix compilation issue

  • Add setStreamMetadata
  • Add getStreamMetadata

  • Internal connection changes
  • Allow creating an event with an existing ID

  • Tight package channnel to connection instance in order to prevent loss on connection drops.
  • Connection has asynchronous operation for real now.

  • Fix date conversion. recordedEventCreateEpoch is no longer exposed.
  • Add waitTillCatchup and hasCaughtUp functions.
  • Add exactStream ExpectedVersion smart constructor. As the result, ExpectedVersion constructors are no longer exposed. You have to use anyStream, noStream, emptyStream or exactStream instead.

No changes

  • Support keepRetrying reconnection strategy.