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Add CmdRetry
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‎README.md

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Retry failed jsonapi requests with retry policies.
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It uses the [`Retry` package](https://package.elm-lang.org/packages/choonkeat/elm-retry/latest/) and the [`jsonapi-http` package](https://package.elm-lang.org/packages/calions-app/jsonapi-http/latest/) under the hood.
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It is greatly inspired by the [`Retry` package](https://package.elm-lang.org/packages/choonkeat/elm-retry/latest/) but aims to handle http requests from the [`jsonapi-http` package](https://package.elm-lang.org/packages/calions-app/jsonapi-http/latest/).
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With this package you can add [`retry`](https://package.elm-lang.org/packages/choonkeat/elm-retry/latest/) policies to [`jsonapi-http`](https://package.elm-lang.org/packages/calions-app/jsonapi-http/latest/) requests errors.
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With this package you can add retry policies to [`jsonapi-http`](https://package.elm-lang.org/packages/calions-app/jsonapi-http/latest/) requests errors.
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You can choose specific errors that will trigger a retry: unauthenticated error, network error, etc...
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You can also send `Cmd`s between 2 failures with the `Http.CmdRetry` module.
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## Getting Started
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Here is an example retrying requests 5 times maximum with a constant interval between retries, only for unauthenticated and unauthorized errors:
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import Http.Retry
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import Json.Encode
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import JsonApi.Decode
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import Retry
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request : Cmd Msg
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request =
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, documentDecoder = JsonApi.Decode.resources "resource-type" entityDecoder
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}
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|> Http.Retry.with
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[ Retry.maxRetries 5
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, Retry.exponentialBackoff { interval = 500, maxInterval = 3000 }
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[ Http.Retry.maxRetries 5
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, Http.Retry.exponentialBackoff { interval = 500, maxInterval = 3000 }
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]
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[ Http.Retry.onUnauthenticatedStatus
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, Http.Retry.onUnauthorizedStatus

‎elm.json

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"license": "MIT",
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"version": "1.0.0",
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"exposed-modules": [
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"Http.CmdRetry",
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"Http.Retry"
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],
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"elm-version": "0.19.0 <= v < 0.20.0",
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"dependencies": {
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"calions-app/jsonapi-http": "1.1.0 <= v < 2.0.0",
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"choonkeat/elm-retry": "1.0.1 <= v < 2.0.0",
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"elm/core": "1.0.5 <= v < 2.0.0",
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"elm/http": "2.0.0 <= v < 3.0.0",
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"elm/random": "1.0.0 <= v < 2.0.0",
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"elm/time": "1.0.0 <= v < 2.0.0",
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"krisajenkins/remotedata": "6.0.1 <= v < 7.0.0"
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},
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"test-dependencies": {}
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}
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}

‎src/Http/CmdRetry.elm

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module Http.CmdRetry exposing
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( with, newAttempt
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, RetryContext
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)
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{-| Tries to perform a `Task` and retry it upon failure, allowing you to execute other `Cmd`s between each failure.
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The following example executes a request with a retry policy when the request fails and
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executes a port before each new retry:
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type Msg
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= OnRetry (Http.CmdRetry.RetryContext Msg Entity)
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| OnEntityRetrieved (RemoteData.RemoteData Http.Error.RequestError Entity)
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type alias Model =
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{ entity : RemoteData.RemoteData Http.Error.RequestError Entity }
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init : ( Model, Cmd Msg )
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init =
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( { entity = RemoteData.Loading }
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, getEntity
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|> Http.CmdRetry.with
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[ Http.Retry.maxDuration 7000
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, Http.Retry.exponentialBackoff { interval = 500, maxInterval = 3000 }
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]
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[ Http.Retry.onUnauthenticatedStatus ]
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OnRetry
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)
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update : Msg -> Model -> ( Model, Cmd Msg )
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update msg model =
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case msg of
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OnRetry retryContext ->
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( model
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, Http.CmdRetry.newAttempt
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executePort
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OnEntityRetrieved
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retryContext
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)
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OnEntityRetrieved entity ->
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( { model | entity = entity }, Cmd.none )
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getEntity : Task Never (RemoteData.RemoteData Http.Error.RequestError Entity)
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getEntity =
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Request.request
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{ url = "<http://endpoint">
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, headers = []
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, body = Json.Encode.object []
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, documentDecoder = JsonApi.Decode.resources "resource-type" entityDecoder
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}
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# Retry
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@docs with, newAttempt
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# Types
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@docs RetryContext
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-}
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import Http.Error
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import Http.Internal as Internal
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import RemoteData
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import Task exposing (Task)
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import Time
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{-| Type used by the module to keep the context of the retry process.
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You will never handle it directly
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`msg` is your `Msg` type and `data` is the data you you to receive from your request.
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-}
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type RetryContext msg data
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= FailedTask (Context msg data)
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| FinishedTask (Task Never (RemoteData.RemoteData Http.Error.RequestError data))
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type alias Context msg data =
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{ partContext : PartContext msg data
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, lastError : Http.Error.RequestError
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}
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type alias PartContext msg data =
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{ startTime : Int
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, failureConditions : List Internal.FailureCondition
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, originalTask : Task Never (RemoteData.RemoteData Http.Error.RequestError data)
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, onRetryMsg : RetryContext msg data -> msg
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, policies : List (Internal.Policy Http.Error.RequestError)
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}
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{-| Attempt a new retry from your update function with the `RetryContext` you received.
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The first parameter allows you to execute a `Cmd` just before the next retry.
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The second parameter is the message you want to send when the request finally succeeded or failed (after all configured retries)
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update : Msg -> Model -> ( Model, Cmd Msg )
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update msg model =
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case msg of
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OnRetry retryContext ->
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( model
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, Http.CmdRetry.newAttempt
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(\lastError ->
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doSomethingWithLastError lastError
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)
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OnRequestDone
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retryContext
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)
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-}
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newAttempt :
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(Http.Error.RequestError -> Cmd msg)
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-> (RemoteData.RemoteData Http.Error.RequestError data -> msg)
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-> RetryContext msg data
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-> Cmd msg
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newAttempt onRetryCmd msg retryContext =
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case retryContext of
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FailedTask ({ partContext, lastError } as context) ->
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Cmd.batch
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[ onRetryCmd lastError
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, retryFromContext partContext
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|> Task.perform partContext.onRetryMsg
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]
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FinishedTask task ->
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Task.perform msg task
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{-| Tries to execute the given task. You will receive a message with the retry context.
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From there you will call `newAttempt` which will handle your request retry, allowing you
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to execute a `Cmd` before the next retry.
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originalTask
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|> Http.CmdRetry.with
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[ Http.Retry.maxDuration 7000
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, Http.Retry.exponentialBackoff { interval = 500, maxInterval = 3000 }
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]
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[ Http.Retry.onUnauthenticatedStatus ]
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OnRetry
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-}
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with :
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List (Internal.Policy Http.Error.RequestError)
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-> List Internal.FailureCondition
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-> (RetryContext msg data -> msg)
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-> Task Never (RemoteData.RemoteData Http.Error.RequestError data)
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-> Cmd msg
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with errTasks failureConditions onRetryMsg originalTask =
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Task.map Time.posixToMillis Time.now
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|> Task.map
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(\nowMillis ->
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{ policies = errTasks
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, startTime = nowMillis
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, failureConditions = failureConditions
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, onRetryMsg = onRetryMsg
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, originalTask = originalTask
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}
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)
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|> Task.andThen retryFromContext
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|> Task.perform onRetryMsg
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retryFromContext : PartContext msg data -> Task Never (RetryContext msg data)
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retryFromContext { startTime, policies, originalTask, onRetryMsg, failureConditions } =
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let
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onError time currPolicies err =
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currPolicies
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|> List.map (\((Internal.Policy nextPolicy) as cfg) -> nextPolicy time cfg err)
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|> Task.sequence
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|> Task.map
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(\nextPolicies ->
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FailedTask
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{ partContext =
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{ startTime = time
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, failureConditions = failureConditions
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, originalTask = originalTask
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, onRetryMsg = onRetryMsg
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, policies = nextPolicies
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}
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, lastError = err
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}
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)
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|> Task.onError (RemoteData.Failure >> Task.succeed >> FinishedTask >> Task.succeed)
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in
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originalTask
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|> Task.mapError (always (Http.Error.CustomError "no error"))
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|> Task.andThen (Internal.convertToError failureConditions)
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|> Task.map (Task.succeed >> FinishedTask)
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|> Task.onError (onError startTime policies)

‎src/Http/Internal.elm

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module Http.Internal exposing (FailureCondition(..), Policy(..), convertToError)
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import Http.Error
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import RemoteData
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import Task exposing (Task)
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type FailureCondition
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= FailureCondition (Http.Error.RequestError -> Bool)
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type Policy x
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= Policy (Int -> Policy x -> x -> Task x (Policy x))
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convertToError : List FailureCondition -> RemoteData.RemoteData Http.Error.RequestError data -> Task Http.Error.RequestError (RemoteData.RemoteData Http.Error.RequestError data)
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convertToError failureConditions result =
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case result of
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RemoteData.Loading ->
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Task.succeed result
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RemoteData.NotAsked ->
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Task.succeed result
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RemoteData.Success d ->
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Task.succeed result
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RemoteData.Failure err ->
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if List.any (\(FailureCondition f) -> f err) failureConditions then
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Task.fail err
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else
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Task.succeed result

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