【F#】Google Drive API のエラーハンドリング

前提

応答: System.Net.Http.HttpResponseMessage [↗]

成功か判定する

200-299

copy, create, export, generateIds, get, list, update, watch.

応答.IsSuccessStatusCode

204

delete^[1], emptyTrash^[2].

応答.StatusCode = System.Net.HttpStatusCode.NoContent

処理が可能なエラーか判定する^[3]

401 (初回) ^[4]

無効なアクセストークン。

応答.StatusCode = System.Net.HttpStatusCode.Unauthorized

429^[5], 500, 502, 503, 504^[6]

時間を置けば解決するかもしれないエラー。

let retryCodes =
    Set [
        System.Net.HttpStatusCode.TooManyRequests      // 429
        System.Net.HttpStatusCode.InternalServerError  // 500
        System.Net.HttpStatusCode.BadGateway           // 502
        System.Net.HttpStatusCode.ServiceUnavailable   // 503
        System.Net.HttpStatusCode.GatewayTimeout       // 504
    ]

retryCodes |> Set.contains 応答.StatusCode

エラーハンドリングの実装例

指数関数的バックオフ^[7]

let randomNumberGenerator = System.Random()

let Backoff (retryCount: int) =
    let currentWaitMilliseconds =
        min
        <| (2. ** float retryCount) * 1000.
        <| 32000.
    let jitterMilliseconds = int currentWaitMilliseconds + randomNumberGenerator.Next(1, 1001)
    System.Threading.Tasks.Task.Delay(jitterMilliseconds).Wait()

エラーハンドリングの擬似コード

let rec TryXX (retryCount: int) =
    match リクエスト処理() with
    | r when r.IsSuccessStatusCode -> 成功時の処理
    | r when r.StatusCode = System.Net.HttpStatusCode.Unauthorized ->
        match retryCount with
        | 0 -> refresh()
        | _ -> failwith "アクセストークン更新処理のエラー"
    | r when retryCodes |> Set.contains r.StatusCode -> backoff retryCount
    | _ -> failwith "未定義なエラー"
and refresh () =
    アクセストークンの更新処理
    TryXX 1
and backoff (retryCount: int) =
    match retryCount with
    | 試行回数の上限 -> failwith "試行回数の上限"
    | _ -> Backoff retryCount
    TryXX (retryCount + 1)

// ...

TryXX 0

end

脚注

1. https://developers.google.com/drive/api/v3/reference/files/delete#response

2. https://developers.google.com/drive/api/v3/reference/files/emptyTrash#response

3. https://developers.google.com/drive/api/v3/handle-errors

4. https://developers.google.com/drive/api/v3/handle-errors#resolve_a_401_error_invalid_credentials

5. https://developers.google.com/drive/api/v3/handle-errors#resolve_a_429_error_too_many_requests

6. https://developers.google.com/drive/api/v3/handle-errors#resolve_a_500_error_backend_error

7. https://cloud.google.com/storage/docs/retry-strategy